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This is to certify that the

dissertation entitled

THE MECHANICS OF THE SIT-TO-STAND
MOVEMENT IN YOUNG CHILDREN

presented by

David Michael Wisner

has been accepted towards fulfillment
of the requirements for

Ph 0 D 0 degree in K111631010 gy

 

 

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THE MECHANICS OF THE SIT—TO-STAND MOVEMENT IN YOUNG CHILDREN
By

David Michael WiSner

A DISSERTATION
Submitted to
IVIichigan State University
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSPHY
Department of Kinesiology

2002

 

 

 

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ABSTRACT
THE MECHANICS OF THE SIT-TO—STAND MOVEMENT IN YOUNG CHILDREN
By

David Michael Wisner

Functioning in daily life as an independent human being inVOl‘JeS “3‘!le the
ability to stand up from a seated position, yet little infomation is available on the sit-to-
stand (STS) movement in children. The primary Purpose of the present study was to
assess the mechanics of the STS movemc’fl1t in young children. A secondary purpose was
to compare the biomechanics of the STS movement among children of different ages.

The subjects were 12 children who fell into one of three age groups: 12-1 8 months (N =
5), 24-36 months (N = 3), and 48-60 months (N = 4). The subjects were videotaped as
they stood up from a seat adjusted to each subject's knee height. Data on forces at the
buttocks and at the feet were collected simultaneously from a force platform mounted on
the stool and a force platform located beneath the feet. The kinematic and kinetic
variables obtained or derived from the analysis of the video and force records incl “ded
movement times; joint ranges of motion; peak hip flexion, hip extension, and knee
€Xtension velocities; velocity of the whole-bOd)’ center 0f gravity; forces at the buttocks
and feet; and peak hip and knee joint moments. The results of the study indicated that the
overal] pattern of the STS movement is well-developed even in the youngest Children and
is similar to that seen in adults. These similarities include: (a) the overall lOiUt motion
Pattern, in which hip flexion and ankle dorsiflexion characterize “15 early part of the

movement while extension of the hip, knee, and ankle (16-, plantar flexion) Occur in the

latter part of the movement; and (b) the pattern of forces at the buttocks and the feet,
which included three types of forces: a posteriorly-directed, propulsive hOIizontaI force at
the buttocks that initiates the movement; a vertical, pTOpulsive force at the feet; and an
anteriorly-directed, braking horizontal force at the feet which acts to cheCk the forward
momentum of the body. Overall, the STS movement in the children was characterized by
fast movement times (c. 1.2 S), relatively fast jOint angular velocities,hip joint moments
that were greater in magnitude than knee joint moments, and the center of gravity being
located behind the base of support at seat—Off. There was a trend toward increasing joint
ranges of motion, velocities, forces, and moments with increasing age, with the oldest
children having results quite similar to adUlts. These resul ts suggest that the oldest
children employed a strategy of transferring momentum from the upper body to the lower
body during the movement as seen in younger adults. While the younger Children
exhibited many of the characteristics of this strategy, they also used elements of a
strategy in which the goal 0f 11pr bOd)’ movements iS to bring the center of rav ‘
to the base of support at the time of seat-off, probably due to a relative lack 01:31;ty close
and postural control as compared to the Older children and adults. While this study "Ce
provides much-needed normative data on able-bodied children, additional research
needs
to be done on how the mechanics of the STS movement in children are affected by
elements of seat design, and on the mechanics of the STS movement in children With

disabilities.

Copyright by
DAVID MICHAEL WISNER

2002

For my wife, whose love, patience, and .gentle prodding helped see me to the end of this
project; and for my father, whose desrre it always was to see me cam my doctorate.

AC KN OWLEDGIVIENT S

This dissertation is the culmination of many years of research and study and
would not have been possible without the help of numerous individuals.

I gratefully acknowledge the assistance Of my committee members: Eugene
Brown, my committee chair, who spent many hours over the years assisting me with all
aspects of this project; John Haubenstricker, who by getting me involved in the Motor
Performance Study piqued my interest in working with children; Robert Hubbard, whose
class on occupational biomechanics started me thinking about seat design and the sit-to-
stand movement; Anthony Paganini, who willingly pitched in at the last minute; and
Jeanne Foley, who was unable to be there at the end but was instrumental at every other
step along the way.

Although not directly connected to this project, other faculty members in the
Department of Kinesiology nevertheless had an indirect impact upon in Crystal Branta,
Gail Dummer, Marty Ewing, Deb Feltz, Bob Malina, Jim Pivarnik, Vern SCCfeldt, and
Paul Vogel.

Appreciation is extended to the Department of Kinesiology for a graduate
assistantship which funded my graduate education, and to the College of Education,
whose fellowship allowed me to build the laboratory in which the research for this

dissertation was conducted.

Special thanks goes to those fellow graduate students who assisted with data

collection and other aspects of this project, in particular Tony Mareno and Miguel

vi

 

 

Narvaez. Also to be acknowledged are all of those graduate students with whom Ihave

interacted over the years.

I am especially grateful for those physical therapists and occupational therapists

with whom I have shared ideas and who convinced me of the importance of this study. In
particular Jan Nestell, Deb Silkwood-Sherer, and above all Linda MacDonald, who
continually encouraged and enlightened me throughout this process.

I am particularly indebted to JoAnn J anes, the graduate secretary in the
Department of Kinesiology, who helped me out of difficulties more times than I care to
remember, and without whom I undoubtedly would never have finished my doctoral
program.

My colleagues in the College of Health Professions at Central NIichigan
University have been a source of ideas, support, and encouragement over the past two
years, and for that they have my gratitude.

I would also like to thank my family, especially my mom, for their support, as
well as all my friends, who have been a source of support and encouragement in this
endeavor, particularly Doreen Espinoza and Jeff White.

Finally, I could not have gotten to this point without my wife, Marguerite

Hal versen, whose love and patience saw me through to the end, and my daughter Brynne,

Whose ever-present smile lifted me up whenever I got discouraged.

vii

 

TABLE OF CONTENTS

LIST OF TABLES ............................................................................... x
LIST OF FIGURES ............................................................................. xii
INTRODUCTION ............................................................................... 1
Purpose of the Study ........................................................................ 3
A Definition of the Sit-to-Stand Movement ............................................. 3
Definition of Joint Angles .................................................................. 5
REVIEW OF LITERATURE .................................................................. 7
The Sit-to-Stand Movement ............................................................... 7
Phases of the Sit-to-Stand Movement ................................................ 7

Commonalities Among Various Phase Descriptions and
Rationale for Phase Descriptions Employed in the

Present Study ...................................................................... 11
Strategies Employed in the Sit-to-Stand Movement .............................. 13
Fundamental Mechanics of the Sit-to-Stand Movement ,,,,,,,,,,,,,,,,,,,,,,,,, 14

Variables Affecting the Mechanics of the Sit-to-Stand Movement ,,,,,,,,,,,,,,,,,, 20
Use of the Arms ........................................................................ 20
Speed of Ascent ........................................................................ 22
Initial Position .......................................................................... 23
Chair Design ........................................................................... 31
Special Populations .................................................................... 34
The Sit-to-Walk Movement .......................................................... 43

The Sit-to—Stand Movement in Children ................................................ 44
Developmental Sequences ............................................................ 45
Development of Rising from a Supine Position ................................... 46
Development of the Sit-to-Stand Movement in Children ........................ 48
The Mechanics of the Sit-tO-Stand Movement in Children ...................... 51
METHODS ...................................................................................... 53
Subjects ...................................................................................... 53
EqUipment ................................................................................... 5 5
Stool ..................................................................................... 55
Videographic System .................................................................. 55
Force Platforms ........................................................................ 57
Synchronization of Video and Force Data .......................................... 59
Data Acquisition System .............................................................. 6O
Biomechanical Model ..................................................................... 60
Anthropometric Measures ................................................................ 62
Procedures ................................................................................... 63
Subject Preparation .................................................................... 63

viii

Data Collection ........................................................................ 63

Data Analysis ............................................................................... 65
Digitization and Video Processing .................................................. 65
Force Data .............................................................................. 66
Variables Obtained .................................................................... 66
Movement and Phase Times. . - - ..................................................... 67
Joint Moments .......................................................................... 67
Variables Reported and Discussed ................................................... 68
Statistical Analyses .................................................................... 69
RESULTS ....................................................................................... 7 1
Right versus Left Side of the Body ...................................................... 71
Movement and Phase Times .............................................................. 71
Joint Range of Motion ..................................................................... 73
Peak Joint Angular Velocities ............................................................ 76
Velocity of the Whole-body Center of Gravity ........................................ 79
Ground Reaction Forces at the Buttocks and the Feet. - .............................. 84
Joint Moments .............................................................................. 86
DISCUSSION .................................................................................. 90
Movement and Phase Times .............................................................. 90
Joint Range of Motion ..................................................................... 95
Peak Joint Angular Velocities ............................................................ 99
Velocity, Momentum, and Kinetic Energy of the
Whole-body Center of Gravity ..................................................... 102
Ground Reaction Forces at the Buttocks and the Feet .............................. . 110
Types of Forces ...................................................................... - 110
Horizontal Momentum and Horizontal Forces .................................. - 112
Amplitude of the Peak Vertical Ground Reaction Force at the Feet ,,,,,,,,, , 112
Timing of the Peak Vertical Ground Reaction Force at the Feet ............. . 116
Location of the Center of Gravity Relative to the Center
of Pressure at Seat—off ........................................................... 1 18
Joint Moments ............................................................................. 120
Strategies Used by Children in Performing the Sit-to-Stand Movement .......... 123
SUMMARY AND RECOMMENDATIONS. ............................................ 125
APPENDIX A: INFORMED CONSENT FORM ........................................ 132
APPENDIX B: QB ASIC PROGRAM INVDYN .......................................... 135
APPENDIX C: MEAN DATA FOR ALL SUBJECTS ................................. 139
REFERENCES ................................................................................ 145

ix

 

LIST OF TABLES

Table l. Phases of the sit-to—stand movement used by various authors

compared to those of Schenkman, et a1. (1990) ............................................. 12
Table 2. Initial starting position used in studies of the sit-to-stand movement. . . . . . 24
Table 3. Age range and mean age of older adult subjects used in studies

on the sit-to-stand movement .................................................................. 35
Table 4. Subject personal characteristics .................................................... 54

Table 5. Mean (isd. where reported) total movement time and,
where applicable, duration of each phase as a percentage of total movement

time reported by various authors (the age range of the subjects in each study
is also reported for comparison) .............................................................. 91

Table 6. Mean (2t s.d. where reported) joint range of motion,

peak hip flexion angle, and time to peak hip flexion (expressed as

a percentage of total movement time) reported by various authors

(the age range of the subjects in each study is also reported for comparison) ......... 96

Table 7. Mean (1 s.d. where reported) peak hip flexion velocity (hipflex v),

hip extension velocity (hipextv), and knee extension velocity (kneeextvel);

and time to peak hip flexion (thfv), hip extension (thev), and knee

extension (tkev) velocities (expressed as a percentage of total movement

time), reported by various authors (the age range of the subjects in each

study is also reported for comparison) ..................................................... , 101

Table 8. Mean (:1: s.d. where reported) horizontal and vertical components
0f the peak velocity of the whole body center of gravity, as well as the
time to peak horizontal (tcghor) and vertical (tcgvert) velocities of the
center of gravity (expressed as a percentage of total movement time),
feported by various authors (the age range of the subjects in each study
18 also reported); the time at seat-off (ISO) is also included for comparison ........... 103

Table 9. Mean (1 s.d. where reported) peak vertical ground reaction force
at the feet (GRFF) normalized per body weight, time to peak vertical GRFF
(expressed as a percentage of total movement time), peak normalized
hip moment (Hip M), and peak normalized knee moment (Knee M) reported
y various authors (the age range of the subjects in each study is also reported
for Comparison), The moments were normalized by dividing by weight (N),
multiplying by height (m), and multiplying by 100 ....................................... 114

 

 

Table C1. Mean (1* s.d.) movement ti mes across ten trials for each subject,
including time in seconds for Phases 1, 2, and 3 (t1, t2, and t3, respectively);
time for Phases 1, 2, and 3 as a percentage of total movement time

(Phase 1 %, Phase 2 %, and Phase 3%, respectively) and total movement
time in seconds (t total) ....................................................................... 139

Table C2. Mean (:1: s.d.) joint range of motion, peak hip flexion angle,

and time to peak hip flexion (expressed as a percentage of total movement
time), across ten trials for each subject ..................................................... 140

Table C3. Mean (:1: s.d.) peak hip flexion velocity, hip extension velocity,

and knee extension velocity; and time to peak hip flexion (thfv), hip

extension (thev), and knee extension (tkev)velocities (expressed as a

percentage of total movement time), across ten trials for each subject ................ 141

Table C4. Mean (:1: s.d.) horizontal and vertical components of the peak
velocity of the whole body center of gravity, as well as the time to peak
horizontal (tcghor) and vertical (tcgvert) velocities of the center of gravit

_ Y
(expressed as a percentage of total movement time), across ten trials for
each subject .................................................................................... 142

Table CS. Mean (1 s.d.) peak vertical ground reaction force at the

feet (GRFF) normalized per body weight, time to peak vertical GRFF

(expressed as a percentage of total movement time), peak normalized

hip moment, and peak normalized knee moment across ten trials for

each subject. The moments were normalized by dividing by weight (N),

multiplying by height (In), and multiplying by 100 ..................................... - 143

xi

 

LIST OF FIGURES

Figure 1. Phases and delineating events of the sit-to-stand movement ,,,,,,,,,,,,,,,,,,, 4
Figure 2. Four-segment, two-dimensional biomechanical model ......................... 6

Figure 3a. Photograph of the experimental set up, showing the adjustable

stool with mounted force platform, special flooring over the force platform
at the feet, and timing lights .................................................................. 56

Figure 3b. Cross-sectional view of the construction of the special plywood
flooring covering the force platform used to isolate only a single foot .................. 56

Figure 4. Diagram of the calibration structure, showing strings weighted

with plumb bobs and suspending reflective styrofoam balls. The coordinates
of the balls and plumb bobs are also shown ................................................ 58

Figure 5. Mean (+ 1 s.d.) movement time (a) and phase ti mes as a percent
of movement time (b) for the three age groups ............................................. 72

Figure 6. Representative time history of the ankle, knee, and hip joint angles 74

Figure 7. Mean (+ 1 s.d.) ranges of motion at the ankle, 10166, and hip joints
during the sit-to-stand movement for the three age groups ............................... 75

Figure 8. Mean (+ 1 s.d.) peak hip flexion angle (a) and the time to peak
hip flexion as a percent of movement time (b) for the three age groups ................ 77

Figure 9. Mean (+ 1 s.d.) peak hip flexion, hip extension, and knee extension

velocity (a) and the time to peak velocity as a percent of movement time (b)
for the three age groups ........................................................................ 78

Figure 10. Mean (+ l s.d.) peak horizontal and vertical velocity of the center
0f gravity (a) and the time to peak horizontal and vertical velocity of the
center of gravity as a percent of movement time (b) for the three age groups ......... 80

Figure 11. Representative plots of the horizontal and vertical components

of the velocity of the whole body center of gravity versus time for Group 1 (a),
GrOUp 2 (b), and Group 3 (c) .................................................................. 83

Figure 12. Representative plot of the vertical and anterior—posterior
ground reaction forces at the buttocks and at the feet versus time ....................... 85

xii

 

Figure 13. Mean (+ 1 s.d.) peak ground reaction force (GRF) at the feet (a)

and the time to peak GRF at the feet as a percent of movement time (b)
for the three age groups ........................................................................ 87

Figure 14. Mean (+ 1 s.d.) peak moment at the hip and knee joints for the
three age groups. Note that the moments were normalized by dividing by

body weight (N), multiplying by height (m), and multiplying by 100 .................. 88

Figure 15. Plot of the horizontal and vertical velocities of the whole body

center of gravity versus time for a relatively slow (a) and a relatively
fast (b) trial ..................................................................................... 108

Figure 16. Representative plot of the kinetic energy of the whole-body

center of gravity versus time. The center of gravity velocity profile for
this trial is shown in Figure 15a .............................................................. 109

Figure 17. Plot of the anterior-posterior ground reaction force at the feet

versus time for a trial in which the subject initiated gait immediately from the
sit-to-stand movement ........................................................................ 1 11

Figure 18. Plots for a single trial of (a) the resultant (i.e., of the buttocks
and feet) anterior-posterior force versus time and (b) the horizontal mOmentum

of the center of gravity versus time. The dotted vertical line indicates the time
at peak horizontal momentum ............................................................... 1 l3

xiii

INTRODUCTION

Functioning in daily life as an independent human being involves having the
ability to stand up from a seated position, walk, run, and change positions when seated,
standing, or lying down. In other words, mobility is essential if one is to be truly
independent (Dawson, Hendershot, & Fulton, 1987; Shumway-Cook & Woollacott, 1995,
p. 239). In fact, for those individuals who have a disability (whether congenital or
acquired through some traumatic injury) one of the major goals of the rehabilitation
process is to help the individual regain as much mobility as possible (Shumway-Cook &
Woollacott, 1995, p. 239). Often times mobility is thought of principally in terms of
locomotion, but the ability to change position from sitting to standing is an equally
fundamental part of mobility (Shumway-Cook & Woollacott, 1995, p.257),

The ability to rise from a seated position on the floor to a standing position
without relying on external support is a benchmark of normal motor development that
typically occurs around eight months of age and is an important prerequisite for the

development of independent walking (Bayley, 1969; McGraw, 1943). While children
continue to sit on the floor for many years after they develop the ability to stand, around
twelve months of age many children are introduced to seats and chairs of apprOpn'ate size
for their stature. From this point on, rising from a seated position on a chair will become

increasingly more common until it eventually becomes the primary type of sit-to-stand

(STS) transfer. Many factors likely influence a child’s ability to rise from a seated

position, including the child’s physical abilities, motor development, and the design of

the chair.

 

While the ability to rise from a supine position to a standing POSi tion develops
quite naturally in most children. those who have a disability often have great difficulty
with this skill, and will therefore more than likely have difficulty rising to a standing

- - - k Wooll 260- V nSant, 1988).
posrtlon from a chair (Shumway-Coo & acott, 1995, p. , a
However, despite the fact that a great deal Of attention has been paid by researchers and
clinicians on the development of initial standing from a supine position, W519“ occurs
around eight months of age, and on the performance in adults (both those with and
without disabilities) of rising from a seated Position on a chair (ranging in age from 18 to
90 years of age), very little research has been conducted on the ability of able-bodied
h‘ldr t ‘ t t din osition from a seated ° ’ -
c 1 en onse o a s an g p p081t1 on on a Chalr, let alone the
ability of children with disabilities to perform the sit-to-

Stand transfer. In fact to dam on”

five studies out of the approximately six ty-five studies on the ‘ ‘16
Slt-tO-St (“ha
and Inoveft‘6

involved children (Brugnolotti, 1992; Cahill, Carr, & A : S’ 1999; F 1‘ an ’ 1987
018, ;

MCMillan, 1998', and Scho1z & Brandt, 1997). Of these only the study by C ah;
'11

. , ’ et al.
1 HVCSU gated the mechanics 0f the movement; the others focused on deVCIOpm
C
. . . "Q11 a
motor control aspects of the movement- Because rehabilitation SpeCialists r 313’ o ”d
normative data from able-bodied individuals to distinguish normal motor behavi
50
n;

abnormal motor behavior when assessing patients with a disability and develOping a

treatment plan (Shumway-Cook & Woollacott, 1995, chap- 5), the relative lack of
normative data on the mechanics of the sit—to-stand transfer in children has resulted in a
serious limitation in helping children with disabilities (re)gain mobility and independence

(LJ. Mach onald, personal communication, May 20, 2001; D. SilkWOOd-Sherer, personal

c:0mrnunication, September 4, 2001 ). It is this general lack of information on the ability of

children to rise from a seated position that this study seeks to address.

Purpose of the Study
The primary purpose of the present study was to assess the kinematics and
kinetics of the movement pattern that occurs when a child rises from a seated position on
a seat to a standing position. This type of biomechanical analysis provides the
information rehabilitation specialists need to better aid children with disabilities in their
ability to stand.
A secondary purpose was to compare the biomechanics of rising from a seated
position among children of different ages in order to determine if any age—related
differences exist which can be used to predict developmental patterns. Such a comparison
helps to fill in the knowledge gap that presently exists and is of use for practitioners who

Work with children on a day—to-day basis.

A Definition of the Sit-to-Stand Movement
The sit-to-stand (STS) movement involves the smooth motion of an individual from a
stationary seated position to a standing position. The STS movement has been
frequently divided into a number of phases (see “Phases of the STS Movement” in
Chapter 2) for descriptive purposes. In the present study, the STS movement is
divided into four phases (see “Phases of the STS Movement” in Chapter 2 for a
rationale behind the selection of these phases; each of these phases and the events that

delineate each are illustrated in Figure l):

 

 

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(1) Flexion-momentum Phase: from movement initiation until just before the buttocks lift
off the seat.
(2) Momentum-transfer Phase: from lift-off until maximum dorsiflexion of the ankles is

reached.

(3) Extension Phase: from just after maximum dorsiflexion of the ankles is reached until
the hips first cease to extend.

(4) Transition Phase: from just after the hips cease to extend until all motion associated
with stabilization from rising is completed, if the individual intends to remain

standing, or until a subsequent movement pattern, such as walking, is initiated.

Definition of Joint Angles
The present study used a two-dimensional sagittal plane representation of the
body. Angular positions of the various joints of the body in anatomical position is defined
to be 0°. In the case of the hip and knee joints, flexion results in an increase in the joint
an gle. In the case of the ankle joint, dorsiflexion results in increasing degrees "of
C1()rsiflexion", while plantar flexion results in increasing degrees "of plantar flexion" (see

1figure 2).

 

 

Shoulder

Trunk
I lflp
Thili
ehf g
Knee
Shank
6 df ekf
Foot
Ankle

I I Toe

Figure 2. Four-segment, two-dimensional biomechanical model. The four segments
c()risist of the trunk, thigh, shank, and foot. The joints (and specific bony landmarks) that
defi ne each segment are the shoulder (acromion process), hip (greater trochanter), knee
(Center of knee joint), ankle (lateral malleolus), and toe (base of the fifth metatarsal). The

joint angles are defined as follows: 9d; = degrees of ankle dorsiflexion, 91d = degrees of

Ce flexion, and 9m = degrees of hip flexion.

 

REVIEW OF LITERATURE

The following review of literature is divided into two major sections. The sit-to-
stand movement is discussed more generally in the first section, including the phases of
the movement, its fundamental mechanics, and the factors (e.g., initial position, chair
design, function ability) that affect the performance of the movement. The second section
is devoted more specifically to the sit-to-stand movement in children, including

developmental topics related to the movement.

The Sit-to-Stand Movement
What follows is a description of the STS movement, beginning with the various
ways that the movement has been divided into its fundamental phases. This is followed
b y an attempt to synthesize these various methods of dividing the movement and
Presenting a rationale for the method used in the present study. The fundamental

mechanics of the STS movements and the factors that affect the fundamental mechanics

 

Of the movement are then described.

Phases of the Sit-to-Stand Movement
As noted in the Introduction, the STS movement involves rising from a seated
QQSition to a standing position from which locomotion or some other motor task can be
initiated. Although the STS is a common movement for most people, it has only recently
been studied in some depth (the first study was conducted in 1963 by Jones, Hanson,

Miller, and Bossom). There are as yet no defined or universally accepted phases of the

 

movement. To date, there have been Several different ways of dividing the movemén t mm
its component phases, although as shall be seen, many of these defined phases are Very
similar to one another. What follows is a description of the various phases into which
authors have divided the STS movement, and the definitions of these phases.

The first to define phases of the STS were Kelley, Dainis, and Wood (1976) who
simply divided the movement into two phases, a Forward-flexion Phase, from initiation
of movement until maximum flexion of the trunk, and an Extension Phase, from
maximum flexion of the trunk to upright stance.

More recently, Schenkman and colleagues (Ikeda, Schenkman, Riley, & Hodge,
1991; Jeng, Schenkman, Riley, & Lin, 1990; Schenkman, Berger, Riley, Mann, & Hodge,
1990; Riley, Schenkman, Mann, & Hodge, 1991; Schenkman, Riley, & Pieper, 1996)

have divided the STS movement into four phases: (1) Flexion-momentum Phase, which
be gins at movement initiation and continues until just before the buttocks lift off from the
seat; (2) Momentum-transfer Phase, which begins at lift-off from the chair and continues
until maximum dorsiflexion of the ankle is reached; (3) Extension Phase, which begins
5 ust after maximum dorsiflexion of the ankle is reached and continues until the hips first
Cease to extend; and (4) Stabilization Phase, which begins just after the hips cease to
ex tend and continues until all motion associated with stabilization from rising is
Completed.

Naumann, Ziv, and Rang (1982) defined the STS in a similar fashion to

Schenkman, et al.: (1) Flexion Phase, from the start of movement until lift-off; (2)
Buttocks-off Phase, from lift—off until the cessation of flexion; and (3) Extension Phase,

from the cessation of flexion until stability is reached in a standing position.

 

ROdOSky, Andriacchi, and Andersson (1989) divided the movement into two
phases, (1) Forward-thrust Phase, from initiation of movement until maximum
dorsiflexion of the ankle, and (2) Extension Phase, from just after maximum dorsiflexion
of the ankle until a standing position is reached.

Kralj, Jaeger, and Munih (1990) divided the STS movement into four phases.

What is interesting in their approach is a more detailed breakdown of what is occuning
while the buttocks are still in contact with the seat. (1) Initiation Phase was defined as
being from the initiation of movement until the point at which the vertical ground
reaction force begins to change in a positive direction (i.e., loading at the feet begins), (2)
Seat-unloading Phase, from the end of the first phase until lift-off, (3) Ascending Phase,
from lift-off until the knees were fully extended, and (4) Stabilization Phase, defined in
an identical manner to Schenkman and colleagues.

Alexander, Schultz, and colleagues (Alexander, Schultz, & Warwick, 1991;

Schultz, Alexander, & Ashton-Miller, 1992) have broken the STS movement down into
two primary phases: (1) Phase I, from quiet sitting until maximum anterior head
di Splacement and (2) Phase H, from maximum anterior head displacement until upright
Stance.

Millington, Myklebust, and Shambes (1992) divided the movement in three
Phases: (1) Wei ght-shift, from first discernible trunk flexion until start of the extension of
the knees; (2) Transition, from the end of the first phase until the trunk flexion ceases;

and (3) Lift, from the initiation of trunk extension until the last discernible trunk

extension at full stance.

 

Kotake, Dohi, Kajiwara, Sumi, Koyama, and Miura (1993) divided the STS into

six stages, each with a particular indicator: ( 1) Stage 1, subject is seated quietly; (2) Stage

2, commencement of trunk flexion and buttocks leave chair; (3) Stage 3, hip joints reach
maximum flexion; (4) Stage 4, ankle joints reach maximum dorsiflexion; (5) Stage 5,
standing; (6), Stage 6, stabilization in standing position.

Roebroeck, Doorenbosch, Harlaar, Jacobs, and Lankhorst (1994), used patterns of
horizontal and vertical velocity of the body’s center of gravity to define three phases: (1)
Acceleration Phase, begins with movement onset and ends when maximal horizontal
velocity of the center of gravity is reached; (2) Transition Phase, begins at maximal
horizontal velocity of the center of gravity and ends when maximal vertical velocity of
the center of gravity is reached; and (3) Deceleration Phase, begins with maximal vertical
velocity and continues until the end of the movement.

Shepherd and colleagues (Shepherd & Gentile, 1994; Shepherd & Koh, 1996)
simply divided the STS into two phases, a Pre-extension Phase and an Extension Phase.
The dividing point between these two phases was lift-off from the seat.

Baer and Ashbum (1995) identified six points that can be used to divide the STS
into three phases: Point 1 corresponds to quiet sitting and defined as 0.1 second prior to
movement initiation, Point 2 to movement initiation, Point 3 to seat-off, Point 4 to mid
Stance when vertical acceleration changes to deceleration, Point 5 to upright stance, and

Poi nt 6 to quiet standing 1 second after achieving upright stance. Based on these points,
the STS can be divided into three phases: from Point 2 to Point 3, from Point 3 to Point 4,
and from Point 4 to Point 5. (Note that Baer and Ashbum did not explicitly define these

three phases; they have been inferred from the definition of the points.) Other authors

10

 

have either not divided the STS into clearly defined phases or have applied the Phas
e

definitions of other authors.

Commonalities Among Various Phase Descriptions and Rationale for Phase Descriptions
Employed in the Present Study
Despite the variety of ways employed in dividing the STS movement into phases,
and in defining these phases, it appears that a modification of the method of Schenkman,
et a1. (1990) is the best candidate for a standard division of the STS movement into its
component parts. First, it is one of the few methods that has appeared in more than one
published study, and the one of the few to be employed by a different group of authors
(e.g., Lou, Chou, Chou, Lin, Chen, & Su, 2001; Vander Linden, Brunt, & McCulloch,
1994). Second, the events which define the different phases are clearly identifiable and
can be measured directly, even without kinetic data. This is not the case with the method
of Kralj, et al. (1990) which relies on kinetic data for defining the first phase, or that of
Roebroeck, et a]. (1994) which relies on the velocity of the body’s center of gravity, a
quantity that is derived from a temporal series of recorded distances. Third, most of the
Phases used by other investigators can be adapted to fit the scheme of Schenkman and
Col leagues (see Table 1). For these reasons, the method of Schenkman, et a1. (1990) was
used in the present study, with the following modification: Phase IV, Stabilization Phase,
is Cal led the Transition Phase. It is defined as the period from complete extension of the
hips until all motion associated with stabilization from rising is completed, if the
indi vidual intends to remain standing, or until a subsequent movement pattern, such as

walliing, is initiated. This dual description is employed because although most previous

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12

studies had the subject remain standing after completing the STS movement, more often
in dailyl living the STS is a necessary precursor to locomotion. Furthermore, it is di fficu It
for young children to stand still after completing the STS movement. Thus this final

phase is often unpredictable.

Strategies Employed in the S it-to-Stand Movement
Two primary strategies have been suggested for the execution of the sit-to-stand
movement (Berger, Riley, Mann, & Hodge, 1988; Hughes, Weiner, Schenkman, Long, &
Studenski, 1994; Schenkman, et al., 1990); the specific terms are from Hughes, et a1.
(1994) : (l) "momentum transfer," in which hip and trunk flexion are used to generate
momen tum which can then be transferred to the whole body, and (2) "stabilization," in
which tr-unk flexion is not used to generate momentum but rather to position the center of
gravity Of the body closer to the base of support at the time of seat-off; in this strategy the
feet are also usually brought closer to the chair, thus making it easier to bring the center
0f gr avi ty closer to the base of support. The momentum transfer strategy is also
CharaCterized by the center of gravity of the body being located behind the center of
pressure (in some cases this may also be behind the base of support) at the time of seat-
Offa a relatively greater amount of trunk and hip flexion, a relatively greater hip flexion
velocity, and a relatively greater hip joint moment but smaller knee joint moment.
'On the other hand, the stabilization strategy is characterized by the center of
gr avi ty being located close to the base of support at the time of seat-off, a relatively
smaller amount of trunk and hip flexion, a relatively smaller hip flexion velocity, and a

relati vely smaller hip joint moment but greater knee joint moment. Of course, these two

13

 

strategies are not mutually exclusive: forward flexion might act both to move the center
of gravity closer to the base of support as well as generate momentum (Hughes, et a1,
1994, called this the "combined" strategy). Which of these strategies is employed seems
to be dependent on the individual’s functional ability, and is influenced especially by
strength and balance. Hence the stabilization strategy is used more by older adults and
other i mdividuals with functional limitations (see the discussion below on "Special

Popu l ations"), while the momentum transfer strategy is used by younger adults and/or

person 3 without functional limitations.

Fundamental Mechanics of the Sit-to-Stand Movement

When describing the fundamental mechanics of the STS movement, the
modification of the phases of Schenkman, et al. (1990) described earlier will be used,
with res ults from other authors being applied to Schenkman and colleagues (1990)

scheme as much as this is possible (see Table 1). In addition, the discussion will assume
that the momentum transfer strategy (Hughes, et al., 1994) is being used, as this appears
to be the typical strategy used by non-functionally-impaired individuals. One difficulty
encountered when trying to compare results between studies, aside from that of different
PMSe descriptions being used, is that most studies restrict the use of the arms during the

mov'i'ttnent—usually by requiring the subject to fold the arms flat across the chest and not

move the arms away from the chest during the movement—but some do not.

Phase I: F lexion-momentum Phase. Recall that the Flexion-momentum Phase

begi 11s with the initiation of movement and continues until just before lift-off from the

seat ~ The movement is initiated by flexion of the hips brought about by a slight flexion

 

14

moment. The remaining hip flexion proceeds as a result of gravitational action and
momentum, with an eccentric hip extensor moment to control the hip flexion. This is
followed, near the end of the phase, by slight flexion of the trunk (Kelley, et al., 1976;
Kral j , et al., 1990; Kotake, etal., 1993). During this phase, the trunk flexes an average of
16°, and reaches maximum flexion in the early part of Phase H (Schenkman, et al., 1990).
In addition, during Phase I, maxima are reached for hip flexion angular velocity, trunk
flexion angular velocity, and neck extension angular velocity (Schenkman, 1990). The
center of gravity of the body travels forward and slightly inferiorly during this phase, with
the horizontal velocity component of the center of gravity reaching its peak at the end of
the ph ase (Roebroeck, et al., 1994; Riley, et al., 1991). While the hip, knee, and ankle
joints a1 I contribute to the forward motion of the center of gravity during this phase as
well as i n Phase II, the greatest contributors appear to be the hip and ankle joints (Yu,
HOHY'CI‘ichlow, Brichta, Reeves, Zablotny, & Nawoczenski, 2000). The propulsive
impulse necessary for this phase is generated by a posteriorly-directed ground reaction
force at the buttocks, followed (possibly; see Discussion section) by a smaller posteriorly-
directed ground reaction force at the feet (Hirshfeld, Thorsteinsdottir, & Olsson, 1999;
Magnan, McFadyen, & St-Vincent, 1996; Pai, Naughton, Chang, & Rogers, 1994).
Phase II: Momentum-transfer Phase. The Momentum-transfer Phase begins with
lift‘off of the buttocks (i.e., seat-off) and continues until maximum dorsiflexion of the
ankle is reached (i.e., the cessation of all lower body flexion). During this phase, the
horizontal linear momentum of the upper body generated during Phase I is transferred to
the thigh segments and contributes to total body anterior movement (Pai & Rogers,

199 1 a; Riley, et al., 1991; Shepherd & Gentile, 1994; Schenkman, et al., 1990). Pai and

15

 

Rogers (19913) and Roebroeck, et al. (1994) found that the major contributor to
horizontal linear momentum is the upper body, while that to vertical linear momentum is
the thi ghs, suggesting that although the upper body horizontal linear momentum may be
transferred to the horizontal linear momentum of the thighs, the thighs are the major
contri buting segments to the vertical linear momentum of the whole body. This result
argue 3 against the interpretation of Riley, et al. (1991), who suggested that the upper body
is the rnajor contributing segment to both horizontal and vertical linear momentum, and
that th 6 horizontal momentum of the upper body was somehow transferred to the vertical
momentum of the upper body. It appears, rather, that the horizontal linear momentum of
the upper body generated by flexion of the trunk and hips is transferred to the thighs just
after 1i f t-off, while the thighs are primarily responsible for the vertical linear momentum
of the whole body. The transfer of horizontal linear momentum from the upper body to
the thigl‘ls has the result of potentially reducing the required lower limb muscle force
(Shepherd & Gentile, 1994).
In this phase the propulsive impulse at the feet changes to a braking impulse
generated by an anteriorly-directed ground reaction force. This braking impulse serves to
Slow the forward velocity and momentum of the body. In addition, there is a vertical
ground reaction force at the feet that generates a vertical propulsive impulse and vertical
velocity of the center of gravity (Hirschfeld, et al., 1999; Pai, et al., 1994; Pai & Rogers,
1990).
Several maxima are reached during Phase II: Maximum flexion of the hip,
{011% wed by maximum trunk flexion, then maximum extension of the neck, and finally

Im‘J‘iimum dorsiflexion of the ankle (Schenkman, et al., 1990). The hip extension

16

 

F

moment, which had been controlling flexion of the hips, reaches a maximum just after

lift-off, as does the knee extension moment, which must limit the flexion of the knee

following transfer of weight bearing from the buttocks and feet entirely to the feet. These
events coincide with near-maximum flexion of the hip and knee (Kelley, 1976;
Schenkman, et al., 1990).

The peak hip extension moment for an adult male of average stature and body
mass ( 175 cm and 70 kg, respectively) is approximately 40 to 60 Nm (Fleckenstein,
Kirby, & MacLeod, 1988; Pai & Rogers, 1991b), while the average peak knee extension
moment for the same individual is approximately 150 Nm (Pai & Rogers, 1991b). The
actual peak hip and knee extension moments will, of course, vary depending upon an
individual subject’s stature and body mass.

Kotake, et al. (1993) calculated that the minimum hip extension moment required
to complete the STS would be 0.7101 Nm per kilogram of body weight (kg BW) and the
minimum knee extension moment would be 0.9:0.1 Nm/kg BW for the subjects in their
study. which were all of similar stature. For a 70 kg individual (assuming that his or her

anthmpOmetric measures were similar to those of the subjects employed by Kotake, et
211-), th‘1 S would equate to a peak hip extension moment of 49 Nm and a peak knee
extension moment of 63 Nm. The former value is well within the range of the values
rPPOITed in the literature (Fleckenstein, Kirby, & MacLeod, 1988; Pai & Rogers, 1991b),
Whereas the latter value is much lower than that reported by Pai and Rogers (1991b). The
reaSQn why individuals produce knee extension moments two to three times greater than
those required to successfully complete the STS is not clear, although restrictions

I“11)Qsed in experimental settings may require greater torque to be exerted.

17

 

During Phase II, the center Of gravity continues to travel forward and upward
reaching its maximum anterior travel by the end of the phase (Schenkman, et al., 1 990).
Also, at the end of the phase, the vertical component of the velocity of the center of

gravity reaches its peak (Roebroeck, et al., 1994; Riley, et al., 1991). At the start of Phase
II, the body is in dynamic stability, as the center of gravity is approximately 7 cm behind
the center of pressure, which is located beneath the heels, at lift-off. At the end of the
phase , however, the horizontal position of the center of gravity is close to the that of the
center of pressure, indicating a quasi-static balance situation (Kelly, et al., 1976; Murray,
Seireg , & Scholz, 1967; Pai, et al., 1994; Riley, et al., 1991; Schenkman, et al., 1990).

Phase 111: Extension Phase. The Extension Phase begins just after maximum

dorsiflexion of the ankle is reached and continues to the end of hip extension (i.e., when
hip angular velocity first reaches 0°/s). Although the hip, knee, and ankle joints all
contrib ute to the vertical motion of the center of gravity during this phase, the greatest
Contfibutors appear to be the knee and hip joints (Yu, et al., 2000). In this phase, hip,
trunk, and knee extension angular velocities reach their maxima, and then decrease to
near 0°, 8 at the end of the phase (Schenkman, et al., 1990).

During Phase III, the center of gravity continues to move upward and reaches its
maximum height by the end of the phase. As at the end of Phase H, the horizontal
POSition of the center of gravity nearly coincides with that of the center of pressure (which
is now located just anterior to the ankles), indicating a quasi-static balance situation
(Kelly, et al., 1976; Murray, et al., 1967; Pai, et al., 1994; Riley, et al., 1991; Schenkman,

6‘ al -, 1990).

18

 

 

N
'I
w.

Phase IV: The Transition Phase. The fourth phase, the Transiti On 9““ ‘
9‘ \s
defined as beginning just after extension of the hip ceases and continui
associated with stabilization from rising is completed, if the individual -
standing, or until a subsequent movement pattern, such as walking, is i
where the individual intends to remain standing, it is difficult to detemli
Be we and of
Phase IV, as the motion due to stabilization is often indistinguishable from/101mg]
postural sway which occurs during normal stance. Although this Situation has not been
studied as an aspect of the STS movement, the mechanics of Phase IV are likely to be
similar to those encountered during postural sway, where perturbations of the body’s
center of gravity toward the edge of body’s base of support are countered by activation of
the body’s postural muscles, especially those associated with the ankle joint (Woollacott,
1 986).
In situations where a subsequent movement (i.e., gait) is to be initiated, as is
usually the case when rising from a seated position, it is also difficult to determine when
the end of Phase IV occurs and when the subsequent movement begins (see below in the
Section "Sit-to-Walk Movement").

Muscular activity during the STS movement. Goulart and Valls-Sole (1999)
Suggest that the lumbar paraspinal (i.e., erector) muscles, quadriceps muscles, and
hamstring muscles are the prime movers for the STS movement, and are activated in the
OrCler listed. They suggest that the activation of the lumbar paraspinals are used to
Straj ghten the trunk prior to movement initiation, that the quadriceps (at least the rectus
feITloris) are involved in the initial hip flexion and in later knee extension, and that the

hamstrings are involved in hip extension during the extension phase of the movement. On

19

 

the other hand, they argue that the ti bialis anterior and abdominal muscles Se
“Q as
postural muscles that act to make any necessary postural adjustments,

obbnsetl in being

prime movers in the actual execution Of the movement.

Variables Ajfectin g the M ec/zam'cs of the Sit-to-Stand Mo L

6/46/11
Use of the Arms

Few studies have investigated the use of the arms in the Pe’fol‘lnance of the STS
movement, despite the fact that arm movement of some kind occurs naturally in
performing the STS (Carr & Gentile, 1994). When the arms are used, they tend to be used
in one of two ways: Either pushing against the arm rests (if available) or seat of the chair
in order to facilitate the movement, or by being thrust forward along with the trunk in

order to increase forward momentum. Both types of arm movements have been

investigated, albeit by few studies.

Several studies have investigated the effects of arm rests. Burdett, Habasevich,
Pi sciotta, and Simon ( 1985), explicitly studied the effects of using the arms to assist in
Performing the STS movement by pushing against arm rests versus using the legs only.
The authors found no significant difference in maximum hip, knee, or ankle flexion
between the arm and no-arm condition for a group of healthy, young adult subjects.
I‘IC>wever, there was a significant difference in the peak hip extension moment, as well as
in the peak knee extension moment, between the two conditions, both variables being
8T6 ater for the no-arm condition. Arborelius, Wretenberg, and Lindberg (1992) found
Sirl’lilar results: the use of arm rests decreased the maximum hip moment by about 50%

and decreased the maximum knee moment by about 30%. In addition, the subjects in

20

E

 

Arborelius, et al.’ s study rated the S TS as being easier (8.00 vs. 8.55 on m
effort) when the arms were used. Furthermore, Ellis, Seedhom, and WE
a reduction in the tibio-femoral vertical fOrce of 18 to 21 %, In using th
STS, the joints of the upper extremity (Shoulder and elbow) are now g§h to aSSiSt the
moments, thereby decreasing the moments required of the hip and 101% . cram? 8””an
. . . J01)!“ To ””19 end

Anglin & Wyss (2000) investigated the arm motion and hand loads enCOUntc-md when

using arm rests, without respect to motion of the lower extremity, and foun d that the

average peak hand load was 134 N, or 19% body weight; a similar result was found by

Alexander, et al. (1991) for older adults.

Carr and Gentile (1994) investigated the other possible use of the arms: thrusting
the arms forward with the trunk at the beginning of the movement. In their study, subjects
were asked to perform the STS movement both in a preferred manner, where the arms
could be thrust forward, and in a restricted manner, in which subjects were required to
keep the elbows flexed at 90° and the arms at their sides. The authors found no significant

di fference between the two conditions in the amplitude of trunk flexion, horizontal and
Vertical momentum of the center of gravity, maximal hip and knee joint moments, and
Ir‘laximum support moment (a net extensor moment generated by the hip, knee, and
aUlcle). However, differences did exist between the two conditions in terms of the
dutation of the maximum support moment, defined as the normalized length of time that
the support moment equaled or exceeded three times body weight, with the restricted
col"ldition having a significantly longer duration. Thus lack of arm use, while not

recIlliring an increase in the maximum support moment (i.e., the hip and knee joint

morl'lents), requires this maximum support moment to be sustained for longer periods.

21

 

Shepherd and Gentile (1994) argue that a brief extension moment (versus the distribution
of a moment of the same magnitude over a longer period of time) may be more efficient
and lead to less muscle fatigue. In other words, even though the body has the ability to
compensate for restricted arm use and does not require an increase in the maximum
support moment, use of the arms makes the performance of the STS movement more

efficient by reducing the required duration of the maximum support moment.

Speed of Ascent

Before discussing those studies that investigated the effects of speed of ascent on
the mechanics of the STS movement, it is important to note that most studies on the STS
made no attempt to control speed, but rather allowed the subjects to select a preferred
speed. Shepherd and Gentile (1994) have noted that even when speed of ascent is not
controlled, movement times for the ST S remain fairly consistent, and typically range from
1.2 to 2 seconds. However, it is clear that initial position has an effect on speed of ascent,
and that variations in speed of ascent affect the mechanics of the STS movement.

Pai, Rogers, and colleagues (Pai, et al., 1994; Pai & Rogers, 1990, 1991b) have
conducted three studies on the effects of speed of ascent on the mechanics of the STS
movement. In all three studies, the authors allowed subjects to perform the STS at three
self-selected speeds: slow, normal, and fast. Across the three speeds, no significant
differences were found in the joint angle profiles of the hip, knee, and ankle, nor in the

bio extensor moment or ankle plantar flexion moment. Significant differences were
Round, however, for the hip flexion moment between the slow and fast speeds (greater for

the fast speed), for the knee extension moment across all speeds (increased moment with

22

 

increasing. Speed), and for the dorsiflexion of the ankle moment between the fast and 510W
speeds and between the fast and normal speeds (in both cases greater for the faSt Speed;
Pai & Rogers, 1991b). Other significant differences between speeds included a decrease
in the time to peak vertical center of gravity velocity with increasing speed and an
increase in peak vertical momentum with increasing speed. In contrast, the peak
horizontal momentum did not change significantly with increasing speed of ascent (Pai, et
al., 1994; Pai & Rogers, 1990). Similar results were obtained by Vander Linden and
colleagues (1994), who found no significant differences in joint angles from normal to
fast speeds, but did find a significantly smaller time to peak force and a significantly
greater peak force for the fast speed (115 vs. 120% BW). In other words, performing the
STS more quickly requires greater joint moments (and ground reaction forces) in order to
accelerate the body more quickly and achieve a faster rise time. The increased velocity of
the STS from slow to fast speeds also accounts for the increase in peak momentum and

time to peak center of gravity velocity.

Initial Position
One of the difficulties encountered when investigating the ST S movement is that a
variety of initial positions were used (see Table 2). Some studies make an effort to control
the initial position of the movement, usually by fixing the seat height at a certain
percentage of knee height, and by fixing the knee angle at 90°. However, these initial
positions are not universal, and therefore comparison between studies is difficult due to
\\\e, variations in initial position. Several researchers have explicitly studied the effects of

initial position on the performance of the STS. The two aspects of initial position

23

 

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26

typica\\y varied are the seat height and the knee and/or ankle angle (i.e., the pOSmon of
the feet relative to the seat), although two studies have investigated the effects 0f initial
trunk angle and trunk motion (Doorenbosch, Harlaar, Roebroeck, & Lankhorst,
1994;Shepherd & Gentile, 1994). Only the effects of initial knee/ankle angle and initial
trunk angle will be discussed now; seat height and other variables related to chair design,
such as arm rest position, use of seat backs, and seat angle will be discussed later.
Munton, Ellis, and Wright (1984) used electromyography (EMG) to investigate
the effect of differences in seat height and initial knee position on muscle activity during
the STS. Two seat heights, 42 and 59.5 cm, and two initial knee positions, “normal (knee
joint at approximately 90° of flexion)” and “feet under chair (knee joint greater than 90°
of flexion),” were used. The authors found no differences in muscle activation patterns
between the two seat heights nor between the two initial knee joint positions. However,
Stevens, Bojsen-Moller, and Soames (1989) found greater hamstring and quadriceps
activity (increased firing rate) when subjects started in a “preferred (i.e., self-selected)
position” versus a “standard (i.e., knee joint at 90° of flexion, ankle joint at 0° of
dorsiflexion) position.” The authors put forth no explanation as to why quadriceps and
hamstring activity would be greater in the preferred condition, as one would expect the
preferred condition to be more efficient than the standard condition.
Fleckenstein, et al. (1988) examined two initial knee joint angles, 75 and 105° of
flexion. They found that the peak hip flexion angle, peak hip flexion moment impulse,
peak hip extension moment, and the peak hip extension moment impulse were all
§\ghificantly greater at an initial knee joint angle of 75°. In addition, the STS movement

took 0.2 seconds longer to complete with the knee joint at an initial angle of 75°. The

27

 

authors suggest that limiting the initial knee-flexion range requires greater trunk and hip
flexion, as well as a higher hip flexion moment impulse, during Phase I, and therefore a
greater hip extension moment is required during Phase II to control the hip flexion.

Vander Linden, et al. (1994), using initial ankle positions of 5 and 18° of
dorsiflexion (95 and 108° of flexion of the knee, respectively), found that ankle and knee
joint excursions were significantly greater at an initial ankle joint angle of 18° of
dorsiflexion, whereas maximum horizontal velocity of the head was significantly greater
at 5° of dorsiflexion. In addition, Phase II was significantly longer for the 5° of
dorsiflexion condition, while Phase HI was significantly shorter for the 5° of dorsiflexion
condition. Vander Linden and colleagues reached a conclusion similar to Fleckenstein, et
al (1988). Namely, with a limited initial knee-flexion range, greater forward momentum
is required to be generated by the upper body (as evidenced by the greater maximal
horizontal velocity of the head in the 5° of dorsiflexion position), and therefore a
prolonged braking force (i.e., hip extension moment) is required during Phase II to
control this forward momentum.

Shepherd and Koh (1996) investigated the effects of three different foot
placements (and, therefore, three knee joint angles) on the STS movement: “feet back,”
with the feet placed such that the heels were aligned with the front legs of the chair (knee
joint angle > 90° of flexion); “feet forward,” with the shank perpendicular to the floor
(corresponding to a knee joint angle of approximately 90° of flexion); and a preferred
condition. The results of Shepherd and Koh’s study confirmed those of Fleckenstein, et
a1. (1988) and Vander Linden, et al. (1994). Namely, as the feet were placed farther

forward, movement time increased, due to the increased distance that the center of gravity

28

must travel from the seat base of support to the feet base of support; and flexion of the
hip, hip flexion velocity, and the peak hip moment all increased significantly as the feet
were placed farther forward. In contrast, both the peak knee moment and the peak ankle
moment decreased when the feet were placed farther forward.

The results of the aforementioned studies on initial position suggest that the
optimal foot placement for the performance of the STS movement is such that the knees
are flexed greater than 90°. When the feet are placed such that the knees are flexed less
than 90°, the movement time increases, and, more importantly, the peak hip moment
increases. Thus, when working with individuals who have hip joint pain or limited
strength in the muscles surrounding the hip joint, it is important that the seating
arrangement is such that they can flex their knees greater than 90° and simultaneously
place their feet on the ground. It is interesting to note that in the study by Shepherd and
Gentile (1994) the preferred condition of all of the subjects involved a foot placement in
which the knees were flexed greater than 90°.

As noted above, two studies have investigated the effects of initial trunk position
and trunk motion on the STS movement. Shepherd and Gentile (1994) studied the STS
under three initial trunk conditions: erect sitting, trunk flexed, and trunk fully flexed. As
might be expected, the initial trunk position had significant effects on the STS movement,
especially at the hip joint. As the trunk position became more flexed, the amplitude of hip
flexion, peak hip flexion velocity, and movement time all decreased. Furthermore, the
onset of extension at the hip and knee joints was affected by the initial trunk position.

Namely, as the trunk became more flexed, both joints began to extend earlier in the

movement and closer to one another in time. In addition, in the fully flexed position, the

29

knee hegat‘l CXtending before the hip whereas in the other initial trunk positions the hip
began extending before the knee. The peak moments for the hip, knee, and ankle joints
were not significantly different across the three conditions. The same was true for the
maximum support moment. However, the duration of the maximum support moment
increased with increasing initial trunk flexion. This result led the authors to argue that a
brief extension moment (versus the distribution of a moment of the same magnitude over
a longer period of time) may be more efficient and lead to less muscle fatigue. In other
words, even though the body has the ability to compensate for restricted hip motion, due
to flexed initial trunk position, and does not require an increase in the maximum support
moment, having the ability to fully flex the trunk during the movement itself makes the
performance of the STS movement more efficient by reducing the required duration of
the maximum support moment (i.e., the required support moment impulse). Recall that a
similar result was obtained by Carr and Gentile (1994) when investigating arm motion.
The study of the effects of initial trunk position conducted by Doorenbosch, et al.
(1994) differed from that of Shepherd and Gentile (1994) in that the two subject groups,
natural and fully-flexed, started with a vertical trunk. While the natural group was
instructed to rise in a natural, comfortable manner, the fully-flexed group was asked to
flex the trunk as fully as possible before lift-off from the seat. Thus Doorenbosch, et al.
were not so much investigating the effects of initial trunk position as they were
investigating the effects of trunk flexion (i.e., motion) on the STS. It should also be noted
that in their study, Doorenbosch, et al. controlled the speed of ascent, and this speed of
ascent was the same for both conditions. Their results indicated no significant differences

between the two conditions in the motion of the knee and ankle joints, though such a

30

difference did exist for the hip joint, as might be expected. In the fully-flexed condition,
the peak hip and ankle extension moments were greater, and the peak knee extension
moment less, than in the natural condition. In addition, the peak hip and ankle extension
moments occurred later, and the peak knee extension moment earlier, in the fully-flexed
condition versus the natural condition. The authors hypothesized that the decrease in the
peak knee extension moment in the fully-flexed condition was brought about by a change
in the activity of the biarticular muscles that cross the knee joint (primarily a decrease in
the activity of the rectus femoris). The authors conclude that performing the STS with full
flexion is one strategy for those individuals with weak knee extensors. It may also be
beneficial for those suffering from arthritis or other pain in the knee joint. However, the
fact that the peak hip moment increased in the fully-flexed condition, would make this

strategy undesirable for those individuals who have arthritis or other pain in the hip joint.

Chair Design

When considering the effects of chair design on the performance of the STS
movement, there are several elements of that design that can be varied, including seat
height, seat angle, seat depth and seat characteristics (such as foam or no foam); angle of
the backrest (if used); and armrest position (if used). Of these elements, seat height has
been most commonly studied. The effects of seat and backrest angle, seat characteristics,
and armrest position have received some attention, while no attention has been given to
seat depth.

As noted, the principal dimension altered in studies on the effect of chair design

on the STS movement is seat height. All of the studies which compared differing seat

31

heights tound similar results. Burdett, et al. (1985) investigated two seat heights, 64 and
43 cm, the latter being considered a “standard height.” The authors found a significantly
greater peak hip extension moment, as well as a significantly greater peak knee extension
moment, for the standard seat height. There were no significant differences in the peak
ankle moments between the two seat heights. As might be expected, maximum hip and
knee joint flexion were also significantly greater for the standard chair.

Rodosky, et al. (1989), who used seat heights of 65, 80, 100, and 115% of knee
height, also found that with increasing seat height, maximum flexion at the hip, knee, and
ankle significantly decreased. In addition, peak flexion moments of the hip and knee
decreased significantly with increasing seat height, whereas there was no significant
change in the peak ankle moment. Likewise, Schenkman, Riley, and Pieper (1996), using
the same seat heights, found that maximum trunk flexion angular velocity, maximum hip
extension angular velocity, maximum knee extension angular velocity, and maximum
trunk extension angular velocity all decreased with increasing seat height.

Alexander, Koester, and Grunawaldt, (1996) also investigated the effects of seat
height, using seat heights of 60, 80, 100, 120, and 150% of knee height, similar to those
used by Rodosky, et al. (1989). Alexander, et al. (1996; confirmed by Alexander, et al.,
2000) found a decrease in rise time with increasing seat height, as well as a decrease in
maximum flexion of the hip with increasing seat height. Similarly, Arborelius, et al.
(1992) found a reduction in the peak hip moment by 50% for 3 hi gh-stand stool (knee
height plus 2/3 thigh length) versus an ordinary chair (knee height), and a reduction in the

peak knee moment of 60% for the high-stand stool. Ellis, et al. (1984) also found a 33%

32

reduction in the tibio-femoral force for a high chair versus a low chair (the height of each
type of chair was not defined).

Aboresius, et al. (1992) and Alexander, et al. (1996) also had subjects self-report
ratings of perceived effort or difficulty for the different seat heights, and found that
perceived effort and difficulty significantly decreased with increasing seat height. The
results of these studies suggest that increasing the seat height reduces the peak extension
and flexion moments about the knee and hip, as well as reducing the maximum flexion of
the hip and knee joints required for the movement, thereby decreasing the difficulty of the
movement, especially for special populations. However, Arboresius, et al. note that the
percentage of body weight supported by the seat of the stool or chair significantly
decreases as the seat height increases. Therefore, a higher seat height places a greater load
on the legs, and would not be the best choice for prolonged periods of sitting.

In addition to studying the effects of seat height, Alexander, et al. (1996) also
investigated the effects of three other chair design variables: backrest recline/seat tilt (95°
recline/0° tilt; 105° recline/ 10° backward tilt; 115° recline/20° backward tilt), foam vs.
no-foam seat, and armrest position (low, forward, standard). Increasing the backrest
recline/seat tilt led to an increase in rise time, an increase in maximum flexion of the hip,
and an increase in the difficulty rating. The presence of foam on the seat also increased
rise time, maximum flexion of the hip, and the difficulty rating. These results were
especially true for the older adults in the study. On the other hand, the arm rest position
had little effect on rise time, flexion of the hip, or degree of difficulty for both younger

and older adults. These results confirm anecdotal evidence that a greater recline and/or

softer seat make rising more difficult. However, for individuals who must sit for long

33

"-r: .

periods, it Seems that a happy medium between sitting comfort and ease in rising must be

reached.

Special Populations

Variations that occur in the sit-to-stand movement in different populations as
compared to the "norm," which is invariably the pattern, mechanics, etc. of the sit-to-
stand movement in younger adult subjects, are discussed in this section. Note that
although children would constitute a "special population" relative to younger adults, the
STS movement in children is discussed in more detail in a subsequent section.

Older adults. When looking at age as a variable affecting the STS movement,
researchers almost exclusively focus on the older adult population. This is due to the fact
that motor function often declines with increasing age (Shepherd, 1987), and that this
decline in motor function may challenge successful performance of the STS movement.
Though many studies define.“older adult” as anyone over 65 years of age, the actual mean
age and age-range of older adult subjects in these studies varies considerably. The mean
age and age-range of older adults used in various studies is shown in Table 3. A further
difficulty when studying older adults is variation in physical condition, although many
studies recruit only subjects that are able to perform the STS and who are free from
severe arthritis or other diseases.

One variable of interest when comparing older and younger adult subjects on the
ST S movement is the total time required to complete the movement (rise time). The

hypothesis is that just as movement time in other motor skills tends to increase with age

after about 40 years (Shephard, 1987), so to will rise time. Yoshida, Iwakura, and Inoue

34

Table 3. Age range and mean age of older adult subjects used in studies of the sit-to-
stand movement.

Studv N Mean Age (yrs) Age Range (yrs)
Alexander, et al. (1991) &
Schultz, et al. (1992)

Group A 23 72.1 63 - 86

Group B 11 84.4 75 - 92
Alexander, et al. (1996) 29 84.0 73 - 93
Baer, et al. (1995) 30 61.6 50 - 80
Hughes, et al. (1994) 22 72.0 64 - 105
Hughes, et al. (1996) 11 78.0 ? - ?
Ikeda, et al. (1991) 9 66.9 61 - 74
Millington, et al. ( 1992) 10 69.0 65 - 76
Mourey, et al. (2000) 7 75.1 71 - 82
Papa & Cappozzo (2000) 35 ? 65 - 81
Vander Linden, et al. (1994) 8 68.8 61 - 78
Wheeler, et al. (1985) 10 75.0 65 - 81
Yoshida, et al. (1983) 20 63.7 ? - ?

35

(1983) found that older adults took significantly longer to perform the STS, a result
supported by Alexander, et al. (1996) and Mourey, Grishin, d'Athis, Pozzo, and Stapley
(2000). However, Alexander, et al. (1991) found that there was no significant difference
in rise time when arms were used to assist in the STS between younger adults and older
adults who were able to rise without using their arms (“Old Able” group), while there was
a significant difference in rise time when arms were used between the Old Able group
and the older adults who were unable to rise without the use of their arms. There was also
a difference, though not significant, between the Old Able group and the younger adults
in rise time when the arms were not used (longer rise time for the Old Able group).
Similarly, Wheeler, Woodward, Ucovich, Perry, and Walker (1985) found that older
adults took longer to rise than younger adults, though this difference was not significant.
It is interesting to note that as the difficulty of the STS movement increases due to
changes in the initial position, such as having the feet placed farther in front of the body,
and chair design, especially decreasing chair height, the differences between younger
adults and older adults in rise time also increases (Alexander, et al., 1991, 1996, 2000).
Thus it appears that when the difficulty of the STS task is low, such as when the'arms are
used and/or the chair height is relatively high (about 115% of knee height), younger
adults and older adults are similar in terms of rise time. However, as the difficulty of the
STS task increases, older adults take progressively longer than the young adults to
perform the STS movement.

As far as joint motion is concerned, Baer and Ashbum (1995) found that healthy
older adults exhibited only a small amount of trunk rotation and lateral flexion, which is

consistent with younger adults. Wheeler, et al. (1985) found older adults to have

36

significantly greater trunk flexion dufing the STS movement than the youngc‘x’r 3d 1,1,5, but
found no significant difference between the groups in maximum flexion of the knee. Papa
and Cappozzo (2000) also found older adults to have a significantly greater trunk flexion
during the STS movement than younger adults. Alexander, et al. (1991) found that in the
without-arms condition, older adults had significantly greater flexion of the trunk, hip,
and knee joints than the younger adults, whereas in the with-arms conditions, the older
adults only differed from the younger adults in maximum flexion of the hip. All of the
above—mentioned authors suggest that the greater trunk flexion seen in older adults is an
attempt to bring the body's center of gravity closer to the base of support at the time of
seat-off. However, Ikeda, et al. (1991) found no significant differences between younger
and older adults in maximum trunk, hip, knee, or ankle flexion when the subjects
performed the STS without using the arms. In addition, studies involving other
populations that used the stabilization strategy (in which the goal is to bring the center of
gravity closer to the base of support; Hughes, et al., 1994) found that the amount of trunk
and hip flexion was actually less than when the momentum transfer strategy was used
(Galli, Crivellini, Sibella, Montesano, Bertocco, & Parisio, 2000; Lou, et al, 2001).
Therefore it is possible that the older adult subjects in the studies by Wheeler, et al., Papa
and Cappozzo, and Alexander, et al. may actually be using the momentum transfer
strategy but must generate greater momentum to compensate for lower extremity muscle
weakness.

The horizontal component of the velocity of the center of gravity in younger
versus older adults during the STS movement was examined by Mourey, et al. (2000).

They studied the STS movement under two different vision conditions (normal and

37

 

blindfolded) combined with two different speed conditions (normal and fast). The authors
found that the peak horizontal velocity of the center of gravity and the horizontal velocity
of the center of gravity at seat-off were both significantly lower for the older adult

subjects versus the younger adults across all conditions, with the difference being
magnified in the blindfolded condition (thus stressing the importance of visual cues for

the older adults). This would seem to be suggest that subjects in this study were using a

form of the stabilization strategy (Hughes, et al., 1994).

Although joint angular velocities would also be of interest when investigating the
effect of age on the STS, few studies report this information. One such study was that by
Ikeda, et al. (1991). In this study, older adults had greater trunk flexion and knee
extension velocities, and smaller hip flexion, neck extension, hip extension, neck flexion,
and trunk extension velocities than younger adults, although none of these differences
were significant. Papa & Cappozzo (2000), on the other hand, did find older adults to
have a significantly greater trunk flexion velocity versus younger adults. They suggest
that the greater trunk flexion velocities seen in older adults is used to generate more
forward momentum to be transferred to the extension phase of the movement (assuming

they are using the momentum transfer strategy; Hughes, et al., 1994).

Similarly, few studies investigated kinetic differences in the STS between younger
and older adults. Ikeda, et al. (1991) found that older adults had a greater normalized
(divided by body weight times height) maximum knee torque and a smaller normalized
maximum hip torque than younger adults. However, neither of these differences were
significant. Schultz, et a1. (1992) used a biomechanical model to calculate the joint

torques required to perform the STS for both younger and older adults using data from

38

 

Alexander, et al. (1991). The differences in the required torques between the gTOupS was
small, with the only significant difference being for the ankle joint. More important,
however, was the fact that the required joint torques for the older adults were all less than
the maximum joint torque strengths reported in the literature (Borges, 1983; Markhede &
Grimby, 1988), leading the authors to conclude that physical strength is not the limiting
factor in older adults’ ability to perform the STS. They suggest that postural stability and
balance is more of a factor in limiting STS performance. On the other hand, Hughes,
Myers, and Schenkman (1996) found that a group of functionally-impaired (defined as
having to use a railing when descending stairs and the inability to rise from a 33 cm chair)
older adults required a knee moment that was 78% of their available strength to rise from
a chair set at knee height versus 34% for younger adults. This difference may reflect, in
part, the use of the stabilization strategy (Hughes, et al., 1994) which results in a
relatively greater knee joint moment. They concluded that while this required joint torque
is less than the older adults' available strength, and while balance and postural stability
may be important, strengthening exercises may help improve STS function; this
conclusion is echoed by Riley, Krebs, and Popat (1997) in an analysis of sit-to-stand
failure. However, several studies that employed a strength-training protocol with older
adults and studied changes in the performance of the STS movement (usually by noting
the time taken to successfully complete a certain number of repetitions of sitting-down
and rising—up, or by the number of successful rises) found no differences between pre-
and post-testing between trained subjects and controls (Judge, Whipple, & Wolfson,

1994; Schlicht, Camaione, & Owen, 2001; Singh, Clements, & Fiatarone, 1997).

39

 

The results of those studies which compared older and younger adults in t h e STS
suggest that only small differences exist between the two groups in most kinematic and
kinetic parameters, the main exceptions being rise time, where older adults take longer to
rise than younger adults, especially as the difficulty of the STS task increases. The
increase in rise time with increasing age and with increasing task difficulty seen in most
older adults, would seem to fit the hypothesis that it is balance that limits STS
performance in older adults. In other words, older adults move their feet back toward the
chair (thus moving the base of support backward) and flex the trunk in order to place the
center of gravity of the body closer to the base of support at the time of seat-off (i.e, the
stabilization strategy); all of these postural adjustments require a greater movement time
(Alexander, et al., 1996; Hughes, et al., 1994; Schultz, et al., 1992). On the other hand,
the greater amount of trunk and hip flexion seen in the studies by Wheeler, et al. (1985),
Papa and Cappozzo (2000), and Alexander, et al. (1991) suggests that some older adults
use the momentum transfer strategy or a combination of the two strategies. This would be
consistent with the results found by Hughes, et al. (1994), in which out of 20 older adult

subjects 11 used the momentum transfer strategy, 4 used the stabilization strategy, and 5

used a combination of the two.

Pregnant women. Lou, et al. (2001) investigated the kinematics and kinetics of the
STS movement at different stages of pregnancy. The authors found that overall (four
different chair heights were actually used; see Table 2) the total movement time increased
from the first through the third trimesters of pregnancy; that the peak hip flexion angle
decreased, while the peak knee flexion angle remained unchanged, from the first and

second trimesters to the third trimester; and that the peak hip flexion moment decreased,

40

 

but the peak knee moment increased, from the first through the third mime-stem These
results are likely due to the increased size of the abdomen, especially during the last
trimester, which changes the body's center of gravity and increases the overall load on the
body and especially on the lumbar spine. Decreasing the amount of hip flexion decreases
the hip flexion moment (and presumably that at the lower back), as does increasing the
movement time (i.e., decreasing the hip flexion velocity), but consequently leads to a
greater knee joint moment.

Obese adults. Not surprisingly, obese subjects exhibit a STS movement pattern
similar to that observed in third-trimester pregnant women: A smaller amount of hip
flexion leading to a smaller peak hip joint moment, thus protecting the lower back (yet
see below in the section on adults with disabilities), but resulting in a larger knee joint
moment (Galli, et al., 2000).

Adults with disabilities. Individuals in this category fall into one of two general
categories: those whose disabilities result from chronic pain, such as lower back pain and
arthritis, and those whose disabilities result from neurological impairment, including
stroke (including resulting henriparesis) and other neurological disorders.

Coghlin and McFadyen (1994) compared the performance of the STS movement
of individuals with lower back pain to that of healthy individuals. The authors anticipated
finding results similar to those which were subsequently found for pregnant women and
obese subjects; namely, that the low back pain subjects would choose a strategy that
would minimize hip flexion and the hip flexion moment, thereby minimizing the stress on
the lower back, but at the same time increase the moment at the knee. However, they

found that while some low back pain subjects exhibited this pattern, others employed the

41

 

strategy of a greater hip flexion and hip moment, but a smaller knee joint momen t. The
authors concluded, therefore, that low back pain subjects do not choose one clear strategy
when performing the STS task.
In one early study on the effects of arthritis on the STS movement, Munton, et al.

(1984) found no differences in the electromyography patterns of the muscles of the lower
extremities between arthritic and "normal" subjects. A more recent study by Munro,
Steele, Bashford, Ryan, and Britten (1998) found that older adult subjects with
rheumatoid arthritis had longer movement times than those reported in the literature for
non-arthritic older adults. Furthermore, the arthritic subjects had lower net knee moments
at seat-off compared to those reported in the literature. Munro, et al. suggested that this
latter result may indicate a choice of the momentum transfer strategy (Hughes, et al.,
1994) so as to avoid large moments at the knee and minimize knee joint pain. However,
the longer movement times of the arthritic subjects is suggestive of the stabilization
strategy (Hughes, 1994). It may be that older adults with arthritis use a combined strategy.
All other STS variables for the arthritic subjects were consistent with those reported in
the literature. Similarly, Su, Lai, and Hong (1998) found that older adult subjects with
osteoarthritis had longer total movement times, a greater forward displacement of the
center of gravity, and a lower peak knee moment than the non-arthritic older adult
subjects in their study, likewise suggesting that arthritic older adults employ a combined
strategy in performing the STS movement.

Several studies have investigated the effects of hemiparesis (usually as a result of
stroke) on the STS movement. Yoshida, et al. (1983) found that hemiparetic subjects

required a greater overall movement time to execute the STS task. Likewise, Hesse,

42

 

Schauer, Malezic, Iahnke, and Mallritz (1994) found that hemiparetic subjeCtS too 1r
significantly longer to execute the STS movement than healthy subjects. In addition, they
found that for the henriparetic subjects the center of gravity was close to the center of
pressure at seat-off, whereas for the healthy subjects the center of gravity was located
behind the center of pressure at seat-off. These results would suggest that the hemiparetic
subjects used a stabilization strategy while heathy subjects used a momentum transfer
strategy (Hughes, et al., 1994). The longer movement times seen in herrriparetic subjects

has also been confirmed by other studies (Cheng, Liaw, Wong, Tang, Lee, & Lin, 1998;

Engardt & Olsson, 1992).

The S it-to- Walk Movement

As noted in the Introduction, although studies generally have the sit-to-stand task
end with quiet standing, in reality more often than not gait is initiated during the last
phase of the STS movement (hence the reason in the present study for naming this last
phase the "transition phase"). Magnan, McFadyen, and St-Vincent (1996) investigated the
effects of modifying the sit-to-stand task with the addition of gait initiation, which they
dubbed the "sit-to-walk (STW) task." The key results from this study were as follows:
First, the temporal characteristics (i.e., time to peak horizontal and vertical momentum,
time at seat-off, and time to maximum height of the center of gravity) of the STW
movement were similar to the STS movement. All of the events tended to occur earlier in
the STW movement, but the differences were all non—significant. Second, while the mean
maximal excursion of the center of gravity in the vertical direction was similar in the

STW compared to the STS movement, the mean maximal excursion of the center of

43

 

gravity in the horizontal direction Was significantly greater for the STW versus the STS
movement. Third, the horizontal and vertical components of the peak momentum of the
center of gravity both were significantly greater in the STW condition versus the ST S. In
addition, while in the STS movement the horizontal momentum decreases slowly to zero
after reaching its peak, in the STW movement the horizontal momentum initially
decreases after reaching its peak, but then began to increase again. Fourth, the position of
the center of gravity relative to the center of pressure at seat-off was similar for both the
STW and STS movements. Lastly, the ground reaction force patterns at the feet were
similar until seat-off for both the STW and STS movements. At the time of the peak
vertical ground reaction force, which occurred shortly after seat-off, the STW condition
showed an increased loading of the stance leg compared to the swing leg, whereas there
was little difference between legs in the STS condition. Furthermore, whereas the STS
movement showed the typical anterior-posterior force pattern of a propulsive force
followed by a braking force, in the STW movement the braking force rapidly switched to

I

a second propulsive force as walking was initiated.

The Sit-to-Stand Movement in Children
As noted in the Introduction, only five previous studies (Brugnolotti, 1992; Cahill,
et al., 1999; Francis, 1987; McMillan, 1998; and Scholz & Brandt, 1997) have
investigated the STS movement in children. Of these, four were concerned with
developmental aspects of the STS movement (Brugnolotti, Francis, Macmillan, and
Scholz & Brandt), and only one (Cahill, et al.) directly investigated kinematic and kinetic

variables, albeit less extensively than in the present study. The subsequent discussion will

 

look first at the developmental aspects of the STS movement, including the deve 10pment
of the ability to stand directly from a supine position on the floor (while the latter
information is not directly relevant to the present study, it does help to provide a picture

of the development of another type of standing movement in children), and then will
proceed to look at what is presently known about the mechanics of the STS movement in
children. First, however, a brief discussion of developmental sequences will be presented,

in order to provide a framework for subsequent discussion.

Developmental Sequences

Two different methods have been proposed for applying developmental phases or
stages to skill development. In the first method, known as the “whole body approach” or
the “composite approach” (Seefeldt & Haubenstricker, 1982), each stage of development
involves characteristic body positions and actions for various segments of the body, such
as the arms and legs. When assessing which stage of development a child is in for a given
skill, the action of the whole body—the arms, legs, and trunk, for example—is observed
and the child assigned to a stage based on the characteristics of the total body action.

The “component approach” (Roberton, 1977, 1978a, 1978b), on the other hand,
treats each body component (arms, legs, trunk, etc.) separately. Thus when assessing
which stage of development a child is in for a skill, first the arm action would be
observed and the child assigned to a given stage for the arm component of the skill, then
the leg action would be observed and the child assigned to a given stage for the leg
component of the skill, etc.. In other words, whereas the composite approach may place

Child A in Stage 1 and Child B in Stage 2 based on overall body action, the component

45

 

approach may have Child A in Stage 1 for each body component (arm, leg, and trunk),
but Child B in Stage 2 for the leg component, Stage 1 for the arm component, and Stage 2
for the trunk component.

The composite approach has the advantage of being less complex, and also take& a
more integrated (in terms of body actions) approach to the development of motor skills.
Although slightly more complex, the component approach has the advantage of allowing
for differences in the rate of development for different body components, thus providing

for an accounting of more subtle changes in the development of motor skills.

Regardless of which method is used, the same basic principles apply to
developmental sequences (Seefeldt & Haubenstricker, 1982). The major principle of
developmental sequences is that individuals pass through the various stages of a skill in a
particular order. In other words, an individual would not progress from Stage 1 to Stage
4, then to Stage 2, and finally Stage 3. It is possible, however, for an individual to skip a

stage or to temporarily regress to the previous stage. In addition, developmental

 

sequences are age-related, not age-dependent. Thus, while mean ages for the attainment
of a particular stage might be given in the literature, it must be understood that different
individuals, all of whom are developing normally, may progress through the

developmental sequence at different rates. h

Development of Rising from a Supine Position

Typically infants are able to walk independently before they are able to

 

independently rise from a supine to an erect position (Bayley, 1969; McGraw, 1943). The I

mean ages at which children are able to achieve these two milestones of development are

46

 

 

11.7 months and 12.6 months, respectively (Bayley, 1969). Furthermore, the abilityto roll
from a supine to a prone position, and the ability to assume an independent sitting
position (milestones that occur before the ability to walk independently), are prereqUiSit§ S
for rising from a supine position (McGraw, 1943).

McGraw (1943) identified two distinct phases in the development of independent

rising from a supine position. The first phase involves the infant first rolling from a
supine to a prone position, and then pushing him or herself up with the hands. As the
Chest is raised off of the floor, first one foot and then the other are placed in contact with
the floor so that the infant assumes a quadrupedal position. From this position, the hands
are removed from the floor and the trunk extended. As noted above, Bayley (1969) found
the mean age at which this phase occurs is 12.6 months.

In the second distinct phase described by McGraw (1943), the child pushes
against the floor with one or both arms in order to rise to a seated position. As the child
approaches the seated position, the lower extremities are flexed in order to place the feet
on the floor, and then as the child pushes with the supporting hand or hands, the knees are
extended and the body is raised to an erect posture. The mean age at which this phase
occurs is between 30 and 46 months (Bayley, 1969; McGraw, 1943).

There is, of course, a relatively smooth transition between the two phases just
described. For instance, by about 22 months of age the child does not roll completely to a
prone position, but simply rolls to one side and then pushes the body up as described for
the first phase (Bayley, 1969; Schaltenbrand, 1928). Altemately, the child may rise to a

seated position as described for the second phase, but then flex the trunk and hips so that

47

 

the bands can contact the floor. The child then rises to an erect position by assuming the
quadrupedal form described in the first phase (McGraw, 1943).
The results of those studies that have investigated the ability of infants and
chi 1dren to rise from a supine position suggest that a relatively mature form of rising is
achieved by approximately 4 years of age (Bayley, 1969; McGraw, 1943; Schaltenbrand,
1928). VanSant (1988), however, was interested in what differences, if any, exist in the
movement patterns of children aged 4 to 7 years in rising from a supine position to erect
Stance. The results of VanSant’s study indicated that while variation certainly existed
among the 120 subjects, the predominant movement pattern at each age was similar to the
mature pattern described by McGraw. Thus it appears that while individual variations in
rising from a supine position may exist after 4 years of age, and immature patterns may

still persist, by this age a relatively mature form of rising from a supine position has been

achieved.

 

Development of the Sit-to-Stand Movement in Children

As has been previously noted, only four studies (Brugnolotti, 1992; Francis, 1987;
McMillan, 1998; and Scholz & Brandt, 1997) have investigated the development of the
STS movement in children. The study by Francis was a cross-sectional study of children
ages 4 to 10 years, whereas Brugnolotti, McMillan, and Scholz and Brandt followed

children (N: 4, N=5, and N=5, respectively) longitudinally from approximately 13 to 24

months of age.

 

In her study, Francis chose to use the component approach (Roberton, 1977) to

describe the development of the STS movement. Francis defined descriptive categories

48

 

 

for each c0IIlponent, and then placed each subject into a particular category. It Should be
noted that in her study, Francis did not restrict the movement of her subjects in any way 1

they were free to place their legs in any initial position and to use their arms in any way

they wished. However, the chairs did not have armrests, although they did have a strai 3hr

back rest. (Interestingly, Francis made no assessment as to whether the subjects used the

back rest in performing the STS movement.)

4 In looking at the arm component, the results indicated that 4- and 5-year-old

Children most frequently pushed on the seat of the chair with the hands, whereas 6— and

10- year-old children tended to push on their legs with their hands, and young adults
either pushed against their legs or swung their arms forward. As far as the trunk
component was concerned, the 4- and 5- year-old children and the young adults fully
flexed their trunk during the movement and trunk extension did not begin until after lift-
off. Recall that this is the normative pattern for the momentum transfer strategy (Hughes,
1994) most often employed by young, healthy adults in performing the STS. The 6- and
10-year—old children, however, more frequently began extending the hip and trunk prior
to lift-off. In terms of the leg component, Francis focused on the initial position and
initial movement of the feet and legs. The results showed that in each age group, the most
common pattern was picking up the feet slightly and repositioning them. Unfortunately,
Francis did not report where the feet were repositioned. It would be assumed, based on
the literature, that the feet would be repositioned such that the knee joint is at greater than
90° of flexion (Shepherd and Gentile, 1994). It is interesting, however, that, in an
unrestricted situation, movement of the feet during the transition from sitting to standing

may be a natural occurrence.

49

 

Bmgnolotti (1992) measured the so-called "V/H ratio", i.e., the ratio of the
vertical velocity of the seventh cervical vertebra to the horizontal velocity of the seventh
cervical vertebra. This ratio was first described by Jones, et al. (1963), who used it to
distinguish between able-bodied subjects and those with neurological impairments.

Brugnolotti found that the V/H ratio decreased for all four subjects during development,
although the factor that caused the decrease (i.e., decreased vertical velocity, increased
hOrizontal velocity, or a combination) was varied.

McMillan (1998) and Scholz and Brandt (1997) followed the same five subjects
longitudinally but focused on different aspects of the sit-to—stand movement. Scholz and
Brandt measured the intertrial variability of the movement trajectories of the center of
gravity of the body and the head, and related this to the body segment motion variability.
The authors concluded that the STS movement is organized mainly around controlling the
body's center of gravity trajectory and, after lift—off from the seat, the horizontal trajectory

of the head, as opposed to controlling individual segmental movements. Furthermore,

 

these results were evident even in the youngest infants (about 13 months of age) and
remained consistent during development.

McMillan (1998) investigated several other aspects related to the development of
movement coordination in the sit-to-stand movement. The aspect studied that is most
relevant to the present study was the predominant movement pattern used by the children
in performing the STS movement. McMillan identified two distinct patterns based

primarily on the amount and speed of trunk flexion (both of these were assessed

 

qualitatively) used in the movement. One pattern, which McMillan called the "forward-

up" pattern, involved little trunk flexion with the body being repositioned at the beginning

50

 

of the mOVement to bring the center of gravity closer to the base of support at Scat-off. A
second pattern, which McMillan called the "diagonal-up" pattern, involved significant
trunk flexion. McMillan also observed that some subjects used a combination of the
forward-up and diagonal-up patterns. Based on McMillan's descriptions, it would seem
that the forward-up pattern is similar in at least some aspects to the stabilization strateg‘y
described by Hughes, et al. (1994), and the diagonal-up pattern is similar in at least some
aSpects to the momentum transfer strategy described by Hughes, et al.. McMillan found
that there was a trend toward increasing use of the diagonal—up pattern with increasing
age, with a corresponding decrease in the use of the forward-up pattern. This is consistent
with Hughes, et al. who suggested that the stabilization strategy (similar to McMillan's
forward-up pattern) would be used by those with less balance and postural control (i.e., at
the younger ages), while the momentum transfer strategy (equal to McMillan's diagonal-
up pattern) would be used by those with greater balance and control (i.e., at the older

ages); the same is argued by McMillan.

The Mechanics of the Sit-to-Stand Movement in Children

To date (not including the present study) the study by Cahill, et al. (1999)
represents the only study of any kind of the mechanics of the STS movement in children.
The authors looked at the performance of the STS among three different age groups: 12 to
18 months, 4 to 5 years, and 9 to 10 years. The kinematic and kinetic variables they
examined were: total movement time, amount of hip flexion and peak hip flexion angular
velocity, and magnitude and time of occurrence of the peak vertical ground reaction force

at the feet. Cahill, et al. found that movement time increased significantly with increasing

51

 

‘ '7

age, with means of 1.0, 1.2, and 1.4 seconds for the three age groups, respectiVely. These
values are generally faster than those reported in the literature for adults (see Table 10 in
the Discussion section for a comparison). Cahill, et a1. offer no explanation as to wh)l
movement time increased with increasing age, or why the movement times were faster
than those reported for adult subjects. Similarly, the amount of hip flexion and the peak
hip flexion velocity increased significantly with increasing age. The authors argue that as
Children develop greater postural and motor control they are able to flex the hips more
and at a greater velocity. This suggests that younger children, who have less postural
control and balance, employ more of a stabilization strategy (Hughes, et al., 1994), which
is characterized by smaller hip flexion, and older children, who have greater postural
control and balance, employ more of a momentum transfer strategy (Hughes, et al., 1994),
which is characterized by greater hip flexion. These results are also consistent with the
developmental changes in movement patterns observed above by McMillan (1998) and
discussed above. Cahill, et al. found that the younger children took longer to reach the
peak vertical ground reaction force at the feet than did the older children (probably due to
lower postural control), whose force patterns were very similar to adults. The magnitude
of the peak force (normalized to body weight), however, was not different among the age
‘ groups and was similar to that reported in the literature for adult subjects. Cahill, et al.
conclude that the STS movement pattern is relatively well-established by 13 months of
age, and is similar to that of older children and adults, the main differences being a faster
movement time in the younger children, increasing hip flexion and hip flexion velocity
with increasing age, and longer time to peak force in the younger children. These latter

two results were attributed to less postural control and balance in the younger children.

52

 

 

NIETHODS

Subjects
Subjects were recruited personally by the author from the children of Michigan
State University faculty, staff, and graduate students; and from the greater Lansing area.
After a parent expressed willingness to have his or her child participate in the study, a
letter was sent to the parent further explaining the purpose of the study and the details of
the data collection procedure. When the parent(s) and child(ren) arrived at the laboratory
(one of) the parent(s) was asked to read and then sign an informed consent form (see
Appendix A). Prior to data collection, approval for this research project was obtained
from the University Committee on Research Involving Human Subjects.

The subjects consisted of 12 children, 4 males and 8 females, in one of three age
categories: 12-18 months, hereafter referred to as Group 1 (N=5; mean age 14.7:t1.7
months); 24-36 months, hereafter referred to as Group 2 (N=3; mean age 26.5:23
months); and 48-60 months, hereafter referred to as Group 3 (N=4; mean age 51.5i5.2
months); one additional subject had to be eliminated from the study due to an
unwillingness to cooperate. The subjects were all healthy individuals with no known
injury, orthopedic problem, and/or disability that limited normal physical development or
their performance of the STS movement. The characteristics of each subject are shown in

Table 4.

53

 

Table 4. Subjects‘ personal charaCteristics.

 

Subject ID Sex Age Height Mass
(months) (cm) (13g)__

1 F 48.0 104.0 15.7
2 F 26.0 84.0 9.6
3 M 29.0 84.5 8.7
4 F 51.0 102.6 17.0
5 M 17.0 74.5 10.9
6 M 59.0 105.8 14.6
7 F 24.5 84.7 10.3
8 F 15.0 77.5 10.1
9 F 48.0 98.6 15.9
10 F 13.0 74.8 9.8
11 M 13.0 75.8 10.3
12 F 15.5 75 .1 9.6

54

 

5100

it

dz:

lOO‘T‘c‘

lleasl

 

Sig“!
qua).
Peri

Equipment
Stool
A custom-built stool was used, Which Can be adjusted from a seat height
(including the height of a mounted force Platform) of 30 cm to a height of 50 cm in 2 cm

increments (see Figure 3). The stool has no back rest and the surface of the seat is flat and

designed for the mounting of a force platform, The height of the stool was adjusted to
100% of the individual's projected calf-length (see SCCtion on .. Anthropometric

Measures") thUS positioning the subject so that the thighs were parallel to the ground.

Videographic System
h ' ‘
Althoug one study Of adults found that the STS movement may not 6 61mm \j
Symmetrical (Lundin, Grabiner, & Jah - . ' l“ 3““
nlgen, 1995). the dtffereflces between the N:
left side were small and therefore althou " ' ° ° °
’ statrst ' rfiC
. . gh lCally Sign ant’ the biomecmmcai
Significance of differences of this magnitude may be srn all (p. 112) ..
qualitative observatio ' ' In addlfion,
n of children performing the STS has suggeste
_ d that
. you .
perform the movement in a fairly consistent, symmetrical manner In fig Children
. the pres
therefo ' . e
re, it was assumed that the STS movement was bilaterally s: etrica1 study,
movement taking place primarily in the sagittal plane. Therefore kinemat' d it!) the
1C at
war ’ . . . , ac
rmlted to two dimensrons. A Single Panasonic S-VHS video camera (mod Ollection
455 . . e] A ~
) was placed With the optical axis of its lens perpendicular to th e Sagittal G
. Plan
sub ect, e oft
J and had a Speed of 60 fields per Second (60 Hz), and a shutter Speed he
0f 1/1000
Qf

a second - - ' am
. Data contained in the literature has shown that this fr e rate and h
S utter Spe
éd

than adequate for the STS movement, which is generally compje‘ed. be
m tween

55

 

lltlfr‘T'umy“

 

. it"s‘ffl 0"" t» '1 t ‘ , r ~~ ..... /'
{Hm 4"," '._.‘§“‘ : ‘ t l

Figure 3a. Photograph of the experimental set up, showing the adjustable stool with

“Ignited force platform, special flooring over the force platform at the feet, and timing
1i ts -

Section of flooring not in

Section of flooring in
contact with force platform

I contact with force platform

 

 

L 1| l

 

 

Force Platform

 

 

 

 

 

Figure 3b. Cross—sectional view of the construction of the special plywood flooring
covering the force platform used to isolate only a single foot.

56

1.0 and 2.0 seconds (Shepherd & Gentile, 1994). The camera lens was zoomed in so that
the field of view (FOV) was as small as possible (thereby making the subject to appear as
large as possible) while still capturing all of the movement and any other relevant
background information (such as timing lights). Prior to the beginning of a data collection
session, a calibration structure consisting of a series of strings, each containing a number
Of reflective styrofoam balls at even increments along its length, suspended from an

overhead aluminum frame and weighted with plumb bobs was placed in the center of the
camera’s FOV (see Figure 4). For the present study the calibration structure consisted of
Six known data points (two balls plus the plumb bob suspended on two strings) at the
follow ing x (horizontal), y (vertical) coordinates, beginning at the bottom left corner (all

coordi mates are in centimeters): (0,0), (0, 60), (0, 120), (123, 0), (123, 60), (123, 120).

Force J’latforms

Kinetic data were collected simultaneously with the videographic data using two

fOI'Ce platforms (AMTI model OR6-5-2000): one placed beneath the subject's feet (note

that the legs of the stool were not in contact with the force platform) and one placed on

the Surface of the seat. In order to ensure that only the right or left foot was in contact

with the force plate beneath the feet during the movement special flooring was used. This

flooring consisted of a piece of plywood that extended over the force platform and was
not in contact with it, and a second piece that was placed on the force platform and

adhered to it using sheet magnets; the overall height of the plywood pieces was the same

(See Figure 3). The result was that the subject placed one foot on the piece of plywood in

dil‘ect contact with the force platform (i.e., the foot on the side facing the video camera)

57

Overhead Frame

,1.—

J
r
I
f

C) (0,120) (R (123,120)

9? (0,60) (D (123,60)

 

 

i (0,0) v (123,0)_

Figure 4. Diagram of the calibration structure, showing strings weighted with plumb
bObS and suspending reflective styrofoam balls. The coordinates of the balls and plumb

bobs are also shown.

58

and one foot on the piece not in contact with the force platform (i.e., the foot on the side

not facing the camera). It was found during pilot testing that the use of this special

flooring did not significantly attenuate or in any other way alter the kinetic data. The

sampling frequency for the force platform was 1000 Hz, although when the kinematic and
kinetic data were analyzed together, this rate was reduced to 60 Hz to match that of the
Video data (this was accomplished by first interpolating data points to reach 1200 points
Per second, and then taking one out of every 20 data points to arrive at 60 Hz). Even
though the STS movement takes only about 1.0 to 2.0 seconds to complete, the force data
Were c ollected for a five-second period to ensure that the entire event was captured. The
force platforms recorded three orthogonal forces (anterior-posterior, medial-lateral, and
vertic a1) and three orthogonal moments about the x, y, and z axes. In addition, the center

0f Pre ssure (i.e., the anterior-posterior point of application of the net ground reaction

force) location relative to the center of the force platform at any given time was calculated
by di v iding the moment about the medio-lateral axis by the vertical force (Kralj, et al.,

1990) - This position relative to the center of the force platform was then related to the x, y

coordinate system of the videographic system.

Synchronization of Video and Force Data

The video record and the force platform data were synchronized during analysis
by matching the observed moment of seat-off on the video record with the moment at
Which the vertical force of the force platform on the seat dropped to zero. This

SYTlchronization was confirmed through the use of timing lights which were visible in the

59

camera's field of view and changed position every 1/1000 of a second, and whi 012

provided an analog signal every second that was superimposed on the force record.

Data Acquisition System
The Ariel Performance Analysis System (APAS) was used to acquire analog data,

to capture and digitize video data, and to filter and smooth the kinematic data. The APAS

Consi sts of: a computer and software to perform the above mentioned functions, a
Panasonic Video Cassette Player (model AG-7150), and a 16-channel A/D board, of
Whic h 14 channels were used in the present study (three for the orthogonal forces from
the fi rst force platform, three for the orthogonal moments from the first force platform,
three f or the orthogonal forces from the second force platform, three for the orthogonal
moments from the second force platform, one for the timing light signal, and one for an

extem a] trigger system). More detail is provided on the use of the APAS in the discussion

on Procedures and the discussion on Data Analyses.

Biomechanical Model
The biomechanical model that was used for all analyses consisted of four linked
rigid bodies: One each to represent the foot, shank, leg (thigh), and the torso; because use
of the arms was restricted, the three segments of the upper extremity (arm, forearm, and
hand) were not included in the model. This model and associated angles are shown in
Figure 2. All segments were assumed to move only in the sagittal plane. The points on the

body that were digitized to define each segment were as follows: foot, base of the fifth

metatarsal and the lateral malleolus; shank, lateral malleolus to the center of the knee

60

joint (i.e., between the lateral condyles of the femur and tibia); thigh, center 0f the knee
joint to the greater trochanter; torso, greater trochanter to the acromion process. Note here
that the torso consists of the pelvis and the trunk but is treated as one segment; i.e.,
movement was limited to the hip joint as opposed to considering movement at both the
hip and lumbosacral joints.
A difficulty one has when performing biomechanical analyses on children,
CSpeci ally those analyses that require information on segmental centers of gravity,
Segmental masses, and/or radii of gyration, is the relative lack of data of this kind on
Children. It is assumed here, of course, that standard anthropometric data on adults, such
as th at derived from Dempster (1955) or Clauser (Clauser, McConville, & Young, 1969),
shoul d not be extrapolated to children. For these reasons, Jensen (1986) set out to
dfitCI‘I‘l—iine body segment mass, center of gravity, and radius of gyration proportions for
Children. Jensen's subjects consisted of males between the ages of four and fifteen. The
reSUIt of his study was a series of regression equations for the above-mentioned variables
based on age. While Jensen's study provides much-needed anthropometric information on
children, there is still a lack of data on children younger than 4 years of age. In fact, the
lowest age limit of Jensen's study represents the highest age limit of the present study.
Nevertheless, despite the inherent dangers of extrapolating data outside of the population
for Which those data have been validated, the decision was made to use J ensen's
regression equations to calculate the segment mass, center of gravity, and radius of
gyration proportions for children in the present study because these equations provided a
mCans for determining, based on age, more accurate segment mass, center of gravity, and

r a(lius of gyration proportions than would have been obtained by using adult data.

61

Anthmpometric Measures

The following direct anthropometric measurements were used in the present

study:

(1) Weight: At the beginning of data collection each subject stood on one of the

force platforms and his or her weight to the nearest 0.1 N was measured.

(2) Height: A moveable anthropometer was used to measure height (stature) in

Centi meters to the nearest millimeter. The procedure used was that prescribed by Gordon,
Chumlea, and Roche (1988).

(3) Projected Calf Length: Projected calf length is the vertical distance from the
prox i 111a] surface of the tibia to the sole of the foot. A moveable anthropometer was used
to me asure projected calf length in centimeters to the nearest millimeter. This value was
then 1.1 sed to adjust the stool to the appropriate height. The procedure used was that
presctfibed by Martin, Carter, Hendy, and Malina (1988).

All anthropometric measurements were taken on the right side of the body, as this

is the standard in the United States (Lohman, Roche, & Martorell, 1988). Note that
segment lengths were not measured anthropometrically, but instead were determined after

the Video images were digitized by measuring the distance between corresponding joint

centers,

62

Procedures
Subject Preparation
Upon arriving at the testing location, parents were reminded of the purpose of the
study and the procedures that would be followed, and were asked to sign the statement of
infonned consent. Once this has been done, the aforementioned anthropometric measures
were taken, and the subject's projected calf length was used to adjust the height of the
Stool to 100% of projected calf length. All subjects performed the STS barefoot, with the
youn ger subjects wearing only a diaper and the older subjects wearing a swimsuit. The
Choice of a swimsuit versus a diaper depended in part on age, but also on the comfort of

the c: h ild and his or her parent.

Data Collection
Each subject was seated on the force platform on the adjustable stool by his or her
parent and positioned in such a way that the edge of the seat contacted the popliteal
regi On. The position of the feet on the force platform was not restricted, although it was
aSS‘JI‘ed that the height of the stool was such that the subject could easily contact the force
platform with the entire plantar surface of the foot, and that the cOrrect foot was placed on
the force platform with the opposite foot off the platform (i.e., the section of flooring not
in Contact with the force platform). The subject’s arms were restricted during the
movement by having the subject hold a small stuffed animal in his or her hands. Once the
requisite position had been achieved, the parent gave the child encouragement to stand
up, at which point an external electronic excitation device was used to trigger the force

Platforms. The video camera was turned on just prior to the first trial and recorded

63

continuously until the end of the data collection period. No attempt Was made to control
the speed of ascent, but rather the goal was to have the subject perform the STS in a
natural manner and at a natural speed (whatever speed that might happen to be). In
addition, no attempt was made to restrict the subject's movement after the STS was
completed, although the older subjects were asked to remain standing for a brief period.
More often than not, the younger children transitioned directly from the STS into a walk
toward their parents (what might be termed 3 "Si t-t0~wa1k pattern“; Magnan, et al., 1996) '
The SUbject continued to perform trials of the STS movement until at least ten acceptable
trials per side of the body were achieved (in some Cases as many as twenty trials per side

of the body were performed). Once thlS was accompl ished, the subj e ct was given 21an

break and then data collection resumed on the OPPOSite side of the body. The side of the
body on which data were collected first (right or left) was randomized, The cfitef‘a used
to determine if a trial was acceptable were:

(1) A complete vrdeo record of the trral was obtained. This 011' terr'on was virtually
guaranteed by continuous running of the video camera.

(2) A complete force record of the trial was obtained. Lack of a can)
record, due to error in triggering the force platform, Was the m0S
cause of making a trial unacceptable.

(3) The subject did not use his or her hands to push off of the stool Orin an

way to assist in performing the ST S. y other

(4) The subjected performed the STS in what appeared to be a "antral man
ner,

without a loss of balance. and neither excessively slowly or CXCessively f
aSt.

64

 

 

 

 

No ' '
Specrfic times or speeds were used for this latter criten'og; t/n’s ware

SUbjective, qualitative measure.

Data Analysis
Digitization and Video Processing
At the completion of data col leCtion the vi d co and force records were reviewed,
and the first five tri 318 from each Side Of the body th at were confirmed to have met the
required performance criteria were selected for anal ysis. Using the APAS the video
record of each trial was first captured. then the beginning and end of the movement were
identified, and then all of the fields of video re rese ‘ ~ 6“
p n tmg the mal were saved» PNS ‘
additional fields before the start of the movement and ten addi ' d Oi
rt
no11a] fields aftei the e
the movement. Because each subject self-selected the speed at W
. hid] the STS was
performed, and the movement trme therefore varied, the nu mbe
r
ult’ . . . . . , Qfrield 'd
rmately digitized vaned from trial to tnal and subject to SUbj 8 Of V1 60
fiet
. - O
vrdeo record of the trial (plus the additional fields before and at‘ flee the
te

_ r) was QOIIIpIetc
data pornts (base of the fifth metatarsal, lateral malleolus cente Sap
’ r of the
kn

(7
’ [befive

trochanter, and acromion process) were digitized by hand for ea h
C field
0

. v. &eater
pornts on the calibration structure were also digitized for each trial It,
- OnCe

had been digitized, the raw coordinate data were filtered and SmOOth e enti
Cd uSi

spline.

65

 

Force Data

The analog signals from each 0f the tWO force platforms passed through an

analog-to-digital converter and the three onhOgonal forces and three orthogonal m omen ts

from each were recorded. The l 000 points of data per second were then reduced to 60

. ve, this
points per second in order to match the freqUeney of the video data. As noted abo

' . , and
was accomplished by first interpolatlflg data points to reach 1200 901mg per second

then taking one out Of every 20 data pOints to arrive at 60 points per second. The force

and video data were then synchronized using the method described above.

Variables Obtained

Using the APAS the following variables were obtaj ned a “gm
I“Cl used for S‘mseq

analysis (two analyses are discussed in more detail below) and/0r
. . , discussion:
(1) posmon (x, y) of the base of the fifth metatarsal, later

ma]
the knee joint, greater trochanter, and aCI'Omion p roce Ieolus, center 0f

’

(2) linear acceleration (x, y) of the base 0f the fifth meta:

’ lateral

(3) angular acceleration of the foot, shank, and thigh Segme Q; ,
nts;

center of the knee joint, greater trochanter, and 30mm;
on

(4) angular position of the ankle, knee, and hip joints;
(5) angular velocity of the ankle, knee, and hip joints;
(6) Position (x, y) and velocity (X, Y) 0f the WhOIC-body center 0
13‘1“): (has
On Jensen's [1986] data); ed

(7) Vertical and horizontal ground reaction forces at the feet and th
e moment

about the medic-lateral axis at the feet; and

66

 

(8) vertical and horizon tal ground reaction forces at the buttOcks_

Movement and Phase Times
As :10th in the Introduction and the Review of Literature, the sTS was divided
' ’ ' at—off),
into four phases: flemon-momentum (from lnltiau‘on of the movement to Se
mOmemllm-transfer (from seat-off to maximum ankle dorsiflexioms extension (from
maximum ankle dorSiflexion to cessation 0f hip exten sion), and transition (from cessatlon
of hip extension to normal postural sway or to the ini ti ation of a subsequent movement);
see also Figure 1. This last phase, because of its highly variable nature, was not included
in the analyses and discussion. The total movement ti me for the STS was dammed to

be the time from the initiation of movement until the: cessation 1 , - i.e., ‘
°f hip extenslmi
end of Phase 3). The movement time (in seconds) for each phase

. 'l'l
Was determmed w g
the defining events listed above; each phase time Was also expre

6d as f
. a ta 6 0
total movement time in order to allow for comparison among (Pi perc en g

S of .
ffereht lengths,
Joint Moments
The moments about the medio-lateral axis of the hip and ,
ee Joints
extension were calculated using the process popularly known as "I- dun}:
nVerse d g

Which has been detailed by (among others) Winter (1990). In this Wes, "
PrecesS free and

d1. . . . bod
agrams of each segment are drawn, beginning With the foot. Based 0n th 3'
e Vertic

. a1
honzontal ground reaction forces located at the center of pressure (DOte t an
at becaus
3 hi
and knee extension occur after seat-off, only the ground reaction forces at h p
t e feet It
. eed to
be conSIdered)’ the moment at the center of pressure about the mediodat l
era axis the f
9 Got

67

 

 

[engflh the ccTiter of gravity location Of the f00t, the mass of the foo t, the [meat-

acceleration at the center of gravi ty 0f the foot, the moment of inertia of the foot, and the
angular acceleration of the foot, one can use the rules of mechanics to calculate the

. . es 211' 6
vertical and horizontal forces and the moment about the ankle joint- once these val"

' ' ' d use a
known, one can then move to the adjolmng Segment above, namely the shank, an

rni ar p ' ce - - it now
si 1 rocedure to determine the f 01' S and moments at the knee you“ (althoug

' ar ' at the
things 6 Simplified somewhat, as one only has to c si 1 r I] forces and moment

ankle, and the mass , moment of inertia, and linear and angular accelerations of the 5mm

. - . ts
at its center of gravr ty). The same process 18 followed to calculate the forces and “10an

at the hip joint, once the knee joint forces and moments have been determined' mthe

present study a Qbasic (version 1.1) computer program was Wri t te ff m a“ oi the
h to pe 0

calculations and iterations necessary to carry out the inverse (Wham ‘ \
. C's
CS pI'OCCdU“

program can be found in Appendix B. For the purposes of com

Dan
301], . .
were normalized by dividing by body weight in newtons, mu I tip] theJOl Ill moments
and multiplying by 100 (Ikeda, et al., 1991).

by h .
613‘” in meters,

Variables Reported and Discussed

After all calculations and analyses were complete, the fonow-
In

81' On
Variables were selected for discussion, and are reported and discussed - p8 of
in th

e

. . ‘ . es
D1 SCUSSIOH sections, respectively: "1‘3

and
(1) Movement times: total movement time, phase times in seco Cl
11 s an
9 d pha
Se

ti mes as a percentage of mOVement time.

68

 

(2) 101m ranges of motl 0113 1”ange of motion (i.e., greatest angle achieved dun'ng

the movement minus the smallest angle achieved) of the hip, knee, and 311“"

jOints.
' ' ' ' kle
(3) Jomt angular velomtleS. the angular Velocities at the hip, knee. and an
joints.
onents of the

(4) Velocity of the center of gr avi ty: the hofiZOmaj and vertical 00m?
on the

velocity 0f the whole-body Center of gravity. In the Discussion secti

velocity of the center of graVity is also used to derive the momentum and

kinetic energy of the center of gravity.

(5) Ground reaction forces: the vertical and h orizontal grou d reacth“ forces a
ll

the feet and at the buttocks.

(6) Ioint moments: the peak extension moments at the hi
. ' S-
D and knee 30““

Statistical Analyses

Granting that the small number of subjects in the present
study
deer

§
sees ”)6

power of any statistical analysis (and thus increases the risk of a T
H e
I)"
Q

analySes were nonetheless used to determine if there were any Statistical] ’ S
differences in the above-mentioned variables among the three age 81‘ 0Up 1y 8i
8 .
The statistical analyses were conducted using the Statistical Package for thm
Sciences (SPSS; version 10.0). In 1110St cases multivariate aHaIYSis of van: 8
(M ANOV A) was used, as each of the variable categories listed above has tlice
wo or m

Ore

dependent Variables (e.g., horizontal and vertical components of the Vel
0City of the
Center

69

 

 

 

of gravity an of
, gular veloc' '
1t1es th
e O
hlp, knee and k
: an le joints)
. In a]
1 cases th
e

si gflificance
1eve] was set at 0!. === 05

70

 

RESULTS

Right versus Lefi Side of the Body

t dlff fences “(ere f0 mpafiflg th:

'n the
' - Therefore I
1' all Of the variables consldel’edo
' ft side of the body f0
r1 ght and le

“vely.
he dcollectt

w 0111 Ti - n' are treate

' h tf 110 s the data fr t . ght- and left—Sidet als

discussront a 0

Movement and Phase Times

can

u ‘ a (the m

' hown 1nF1gut65
tlmeS for each age group are s .
The mean movement “d“
' ' A PC
' cross ten trials for each SUbJCCt can be found in Table C1 of P
movement times a

d
“owe
h tal mean movement time for Group 1 was the greatest at 1.2 "$0.4 sfio

C).T e to

closely by the Group 3 at 1.2 :03 s; the mean movement time {is not significantly
different between these two groups. However, the mean move ht time for the Groupz
was significantly shorter (0.9 1:02 s) than both of the other grou s (p < .01)‘

age groups. Group 1 had the greates‘ variability in movement ”’he with a St oft/’6 three
deviation equal to 31% of total movement time, followed by Group 3 at 279 data

2 having the smallest variation at 24% 0f movement time. , “If”, Grail!J

The mean times for each age group for Phases 1’ 2’ and 3 0f the movement,
CXpressed as a percentage 0f total movement time, ls shown m Figure 5b (th

an phase

e me
times and phase percents across the ten trials for each SUbJect are also sh0wn in Table
C1) AS a Whole the subjects spent 1““ over half 0f the total movement ti

me in Phase 1
(O 6 +0 2 s or 53 +10%) As for the remainder of the movement time,

71

 

     
 

'A" Group 1
(”at 6"”, 2
1.490 9’0"? 3

   

 

1.0

3.8

Time (s\

0.6

0.4

0.2

 

 

0.0 ,

(a)

60

50

30~

 

 

20

Percent of Movement Tlmo (‘36)

10

 

Phase 1 PM“ 2

 

(b)

1; Significantly different from Group 1 (p<.05)
S‘gmficamly different from Group 2 (p<.05)

Figllre 5 Me ' '
. ' an (+ l s.d.) movement time (a) and phase times as a
time (b) for the three age groups- Percent of movement

72

 

approximately one-third was Spent in Phase 2 (0.2 :t 0.1 s or 16 j: 11%) and two—thirds in
Phase 3 (0.4 i0.3 s or 31 il7%).
In comparing the three age groups, Group I spent Significantly longer in Phase 1
(P < ~01) and Phase 2 (P < '05) than did Group 3 (55 21:1 1% vs. 49 i9% for Phase 1 and 20
:t12% vs. 14 i9% for Phase 2), and Significantly less time in Phase 3 (p < .01) than did
Group 3 (25 i17% vs. 38 $1570) Groups 1 and 2 had similar phase times (as a
percentage of total movement time) except for Phase 2, for which Group I spent a
significantly longer time (20 i12% vs. 13 ill%; p < .05). Groups 2 and 3 significantly

differed from each other only in Phase 1, for which Group 2 Spent a significantly longer

time (56 11:9% vs. 49 219%; p < .01).

Joint Range of Motion

Although the groups differed in the total range of motion of each joint, the overall
pattern of joint involvement was similar for each group. A representative graph of joint
angular position versus time is presented in Figure 6. In addition, the mean total range of
motion for the ankle, knee, and hip joints is shown in Figure 7 (the mean data for each
subject can be found in Table C2 of Appendix C). The mean ranges of motion at the
ankle, knee, and hip joints were the greatest for GI‘OUP 3 (35 114°, 83 :22°, and 113 :16°,
respectively), and were significantly different (p < .01) from both Groups 1 (29 112°, 61

:1 60, and 90 i170) and 2 (25 :9°, 60 115°, and 86 il4°), which were not significantly

dfiferent from each other.

73

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75

The mean peak hip flexion angle and the mean time to peak hip flexion for each
group (expressed as a percentage of total movement time) are shown in Figure 8; the
mean data for each subject can also be found in Table C2. The mean peak hip flexion
angle was also the greatest for Group 3 (127 19°), and was significantly greater (p < .01)
than both Groups 1 (110 113°) and 2 (103 112°). The mean time to reach peak hip flexion
was similar for all three groups (Group 1 = 38 112%, Group 2 ___ 43 18%, Group 3 = 40

16), although the time for Group 1 was just significantly less (p < .05) than that for Group
2. There were no significant differences between Groups 1 and 3 and between Groups 2

and 3.

Peak Joint Angular Velocities
The mean peak angular velocities reached during hip flexion, hip extension, and
knee extension are shown in Figure 9a, while the times required to reach peak hip flexion,
hip extension, and knee extension angular velocities (expressed as a percentage of total
movement time) are shown in Figure 9b; the mean data for all subjects can be found in
Table C3 in Appendix C. The mean peak angular velocities during hip flexion, hip
extension, and knee flexion for Group 1 (64 124°ls, 206 168°ls, and 143 162%,
respectively) were significantly less (p < .01) than for Groups 2 (89 125%, 278 177%,
and 208 173%) and 3 (105 146°ls, 264 182°ls, 206 173°ls), which were not significantly
di fferent from each other.
The mean time, as a percentage of total movement time, taken to reach peak hip
flexion was significantly less (p < .01) for Group 1 (18 112%) than for Groups 2 (26

19%) and 3 (25 16%), which were not significantly different from each other. On

76

 

IAge Group 1
DAge Group 2
IAge Group 3

 

 

 

 

 

 

 

 

160
1

140 a

120 ‘

60‘

4o-

20]

(a)

 

 

 

 

ifferent from Group 1 (p<.05)
ifferent from Group 2 (p<.05)

 

 

 

 

601

50-1

a
0 0
w 3 2

$9 08.... 2.0626: .0 «season

ficantly d
ficantly d

(b)
"' Sight
’( Sigm

Figure 8, Mean (+ 1 s.d.) peak hip flexion angle (a) and the time to peak hip flexion as a

percent of movement time (b) for the three age groups.

77

400
7

 

IAge Group 1
* UAge Group 2
350 ‘ IAge Group 3

 

 

 

300 ‘

 

250 J
200 -

a:
150 ‘

Angular VelocW (“9“)

 

100 -

50‘

   

 

 

Hlp Floxlon Hlp Extenslon Knee Extension

90«
sol

70‘

 

50‘

Percent of Movemam Time (96)

 

 

 

Hlp Flexlon HIP Extension Knee Extension

Q3)

* Significantly different from Group 1 (IX-05)

Figure 9, Mean (4. 1 s.d.) peak hip flexion, hip extension, and knee extension velocity (3)
and the time to peak velocity as a percent of movement time (b) for the three age groups.

78

the other hand, the mean time to peak hip extension velocity was not significantly
different among the groups (Group 1 = 75 $11%, Group 2 = 72 $12%, Group 3 = 76
$11%), nor was the mean time to peak knee extension velocity (Group 1 = 74 $14%,
Group 2 = 72 $12%, Group 3 = 77 $1370). As expected, peak hip flexion velocity
occurred prior to seat off, with peak hip and knee extension velocities occurring close to

each other and to the Phase 2-Phase 3 transition point.

Velocity of the Whole-body Center of Gravity
The mean peak horizontal (anterior-posterior) and vertical components of the

velocity of the center of gravity (CG) of the whole body, as Well as the mean time taken
to reach peak horizontal and vertical velocity (expressed as a percentage of total
movement time), for each group are shown in Figures 1021 and b, respectively; the mean
data for each subject can be found in Table C4 of Appendix C. The mean peak horizontal
velocity of the CG was significantly less (p < .01) for GrOUp 1 (22.5 $14.5 cm/s) than for
Groups 2 (33.9 $10.7 cm/s) and 3 (37.0 $15.2 cm/s), which were not significantly
different from each other. The same was true for the mean peak vertical velocity of the
CG: that for Group 1 (19.4 $7.5 cm/s) was significantly less (p < .01) than for Groups 2
(33.4 $7 .6 cm/s) and 3 (37.0 $13.9 cm/s), which were not significantly different from
each other. Studies involving adult subjects have reported peak horizontal and vertical
velocities as being of similar magnitude (Riley, et al., 1991). In the present study the
mean peak horizontal and vertical velocities were similar in magnitude to each other, and

were significantly correlated (p < .01), but the correlation was relatively low (r = .42).

This result is not surprising, as there was a great deal of between-subject variability

79

60

IAge Group 1
DAge Group 2
lAge Group 3

Velocltv (CW9)

 

Horizontal Vert|cal

(a)

Percent of Movement Time (96)

 

Horlzontal

Vertlcal
(b)

* Significantly different from Group 1 (p<.05)
’i Slgmficantly different from Group 2 (p<.05)

Figure 10. Mean (+ 1 s.d.) peak horizontal and vertical velocity of the center of gravity

(a) and the time to peak horizontal and vertical veloc'
ity of the center of '
percent of movement time (b) for the three age groups. gravrty as a

80

(see Table C4).

The mean time taken to reach peak horizontal velocity of the CG was significantly
greater (p < .01) for Groups 1 (58 227%) and 2 (56 :17%) than for Group 3 (39 113%);
there were no significant differences between Groups 1 and 2. There were no Significant
differences among the three groups in the mean time taken to reach peak vertical velocity

(Group 1 = 68 $15%, Group 2 = 7 1 $13%, Group 3 = 65 114%),

Because linear momentum is dependent in part on linear velocity (and in part on
body mass), the horizontal and vertical velocities of the CG provide a normalized
measure of the horizontal and vertical linear momentum of the CG (i.e., momentum
divided by mass). Although variation did exist from trial to trial and subject to subject,
most trials exhibited the relationship between horizontal and vertical velocity (and
thereby horizontal and vertical momentum) illustrated in Figure 11, which consists of a
representative plot from each of the three age groups. In this pattern, the lowest point of
the vertical velocity of the CG coincides with the peak horizontal velocity of the CG.
Then as the horizontal velocity decreases the vertical velocity increases until it reaches its

peak.

On average (with the exception of Subject 5) the peak vertical velocity of the CG
occurred after the peak horizontal velocity had been reached. The difference in time
between peak vertical velocity and peak horizontal velocity tended to increase with each

age group: a difference of 10% of total movement time for Group 1, 15% for Group 2,
and 26% for Group 3 (see Figure 11). This time difference was significantly greater (p <
.01) for Group 3 versus Groups 1 and 2, which were not significantly different from each

other. On average, peak horizontal velocity tended to occur close to seat-off (the Phase 1-

81

. esentafiVC PlOts of the horizontal
Figure 11' Repf ~ , and Vert' t f the
velocity 0f the WhOlC bOd)’ Center Of graV1ty V5. t1 me for Gfgilgolnagnaos“: 7- 0°),

and Group 3 (C)-

 

 

onents of the
), Group 2 (b),

 

A
O

Phasel Phasez

No)
to
"to".

 

VGIOCIW (emls)

 

 

 

 

 

 

O 1 o 2 o :3 o 4 o 5 o s o 7 o 8 0
Percent of Movement Time (7°)

  
   

 

 

 

 

 

 

 

  

Phase 3

ooooo
'0
o

”Horizonla‘
..... Vertical

100

90

 
   

 

(a)
4 O
Phase1 phaseZ P118593
35
30 “a
a;
E 25 "
3 20
g 15
'5 to -.
> “x.
5 ~--
0 ‘3 ,.OC"'
.5 N ' '-- - .-
-\o 1 . , ‘-— Horizontal
0 1o 2 0 3GP 40 so so 7 ‘ Vertical
ercent of Movement Ti 0
on "‘em) 8" 90
100
40
1 Phase 2
35 a ‘. PhGSQ 3
so
a
E 25
3 20 “~.
g 15 .
7, 1o ‘
>
5
o
-5
\Horlzont
~10 -Vertlea‘ “'
so 40 so so 70 a
(0 Percent of Movement Time (°/.) 0 9 0 1 0 0
Figure 11.

83

h rizontal
Phase 2 transition point) for Groups 1 and 2. However, for Group 3 the peak 0

- ' 11 . There
velocity occurred about 10% of movement time prior to seat-off (see Figure )

. . . . . ' ub'ect on the
was, hOWCVer, considerable variability from trial to trial and subject to s j

' l
' ' the ak vertlca
occurrence 0f peak horizontal velocity relative to seat-off. The timing of P6

s 2
‘ ' oint for GrouP
velOCit)’ OCCurred, on average, close to the Phase 2-Phase 3 transrtion p

. . Fi ure 11)-
and 3, but about 7% of movement time before this point for Group 1 (SE56 g

I
Ground Reaction Forces at the Buttocks and the Fee

' 121th
396d was ISO

In the present study the foot on the side of the body being videot

- this
' ' (Ed,
80 that only the forces and moments assoc1ated Wlth that foot were 111638“

0N“U
facilitated the calculation of joint moments. However, virtually all of the gt

iorm.
' C \a‘
force data reported in the literature 18 for two feet measured With a single fOtC P

Thereiore, in order to compare the results of the present study With those reported for
. the v
other children, symmetry was assumed and alues f '
adu\ts and or a Slnglefoot was
doubled ‘0 arrive at values representative of both feet.
During initial sitting subjects supported (0“ average) about 35% or

weight on the buttocks and about 15% 0f total bOd)’ WClght on the feet. The body

movement was initiated by a posteriorly-dlI'BCth, propulsive horizontal fOr

. . tom the
buttocks followed shortly by a postenorly—directed force of the feet. At abou t t

he s

time as the posterior force at the feet was initiated there began a periOd of loading

(vertical force) at the buttocks and unloading (vertical force) at the feet. Onset of Wm.
10a}

loading of the feet occurred well before seat-off (175 ms prior to seat-off, on average) and

coincided with the onset of an anteriorIY-diteCth, braking hGrizontal force at the feet

84

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85

 

 

 

 

WhiCh tended to peak around seat-off. An example of this pattern for a subject in Group 3

is shown in Figure 12.

The mean peak vertical ground reaction force at the feet (GRFE’normali zed to

bOd)’ Wefight-and the mean time taken to reach the peak vertical GRFF (expressed as a

. . ' ; the
percentage 0f total movement time) are shown in Figures 13a and b. TCSPCCUVCIV

Pendix C. The mean peak
) than for
1 5 5

mean data for all subjects can be found in Table C5 in Ap

GRFF for Group 1 (137 $31% body weight) was significantly lower (P < '01

u 3 (
Group 2 (163 $49% body weight), but was not Significantly different from Gro p

On
other.
133% body weight); Groups 2 and 3 were not significantly different from each

01)

( 4.

the other hand, the mean time taken to reach peak GRFF was significanl‘y less p

t

. W616 “0
for Group 3 (53 $13%) than for Groups 1 (66 $2193) and 2 (67 $23070),Wh‘c“

- - - n ther F 11 0gamed
Significantly different from 639 0 ' or a groups, the Inean peak GRFF

after seat-v0“, although it tefldfid to occur closer to seat—off Wi th increasing age (compare

Ta‘o\es C5 and Cl).

Joint Moments

The mean peak hip and knee moments are shown in Figure 14 (a,
Q

all subjects can be found in Table C5 in Appendix C). NOte that the mom can data far
ems

. I o I ' ' . . were
normalized by diViding by the subjects body weight (in newtons) multi l
’ p ying

by the

subject's height (in meters), and then multiplying by 100. The mean normal
lzed peak .
hip

moment increased significantly (p < .01)with each subsequent age group (G

$6. 6, Group 2 = 14.6 $6.4, and Group 3 = 31.0 $13.4). For the knee joint Group 3
again

h ad the greatest mean normalized peak moment (15.2 $5.4), and this was significant
3’

86

 

 

250

    
    

  

lAgo Group 1
one Group 2
IAgo Group 3

200

 

a
u
C

W 17° Bony Walnut)

 

(%l

 

60

50

40-

Percent of Movement Tlm‘

20~

 

 

 

 

(b)

11' gfognificantly different from Group 1 (p<.05)
lgl'llficantly different from Group 2 (p<.05)

FigIIre 13 M
. ean (+ 1 s.d.) peak ground rea '
to ction force (GRF) at
peak GRF at the feet as a percent of movement time (b) for thehtehfxt (a) and the time
age groups.

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88

 

 

greater (p < .05) than that for Groups 1 (6.2 15.8) and 2 (9.4 15.8). Group 2 also had a

significantly greater (p < .05) mean normalized peak knee moment than Group 1-

89

 

 

‘f—Jfi ..

 

 

 

l

l

l

1
mm.

DISCUSSION

Movement and Phase Times

. . . re orth
As might be expected, movement time is the Single most commonly P

. . - - ' 'de the STS
result among all of the sit-to-stand studies. LikeWise, the studies which dIVl

, . e, t lcally
into PhaSeS usually provide a break down of the time required for each phaS W

55
. . ' he data aCI‘O
expressed as a percentage of total movement time in order to normalize t

. termed a
SUbjCC ts. In the present study subjCCtS performed the STS at What ‘5 often

' s can
u . eflt t‘me
"normal, " "self-selected," or "natural Speed Thus comparison of movem

. me WaY'
- t in SO
only be made with those studies that did not control the speed of movemC“ S

we
- _ I study
The total mean movement time for the entire group of subjects m the 91-656“

1.11204 5. This result is simllar ‘0 the - S fOllnd by Cahill, et a1_ (1999) {0
group of children. The mean movement times reported by Various authors for adUlt
subgects for the STS perforn‘led at a natural speed is shown in Tab]
6 5' “1035 found for

children in the present study and by Cahill, at al. are reported for Comparj
8

. . , 0
be noted that age ranges for the groups 1“ Cahill, at al. 5 Study differ from I). (Its/7011M

the current study, and were as follows: 1.1-1.5 years for Group 1’ 41-5 0 ose 08¢:de
Ears
2, and 8.6—9.9 years for Group 3.) The range of movement tim es reported . for GrOle
IS re a .
. . t1
large (1.0-3.3 3), although most studies found times between 1. 5 and 2 0 s W Ver
° ' hat is

interesting is that the total movement times for young children as 1:0qu .
In the present
study and by Cahill, et al. are substantially less than those reported for adults Sinc
’ ‘3 Seat
height in both studies was set at knee height (and thus normalized), Seat height shou1 d
not

be a factor in movement time. One possible cause of the difference in movement times is

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that even though the adult subjects were asked to perform the STS at a naturaj speed, they

may have performed the mo vemem more self-consciously. and therefore more slowly-

Anabel” POSSibili‘y is that the Children (especially the younger children) were eager to

stand up and move toward their parents and Were thus likely to stand up as quickjy as

possible; Cahill, et al. reported similar behavior, Indeed those studies that had subjects

rise at a self-selected "fast" Speed reported total movement times similar to those found in

the present study and by Cahill, et al. (Mourey, et al., 2000: 1.0 s for young adults, 1.4 S

for older adults; Pai, et al., 1994: 1.4 s; Pai' & Rogers, 1991. 1.2 8, Papa & CappOZZO’
2000: 1.2 s).

- t
Also shown in Table 5 are the mean duratl ons (as a Percentage of iota1 movemen
' - -‘ of
time) of the three phases of the STS reported in the li terature, q s noted in the renew

literature, there is no overall agreement on the definition of phases for the 513,Thereiore

the only durations reported in Table

5 are those for phases that could clearly be identified
with one of the three phases used in the present StUdY- Not Surprisin 1 h
g y t is

easily be done for Phase 1, which ends at seat-off, an even t that is dead COlIId most
reported in most studies. Unfortunately, the studies by schenkman and CO defined and
et al., 1991; Riley, et al., 1991; Schenkman, et al., 1990), fr 0m which the zleagues (Ikeda,
definitions for the present study were derived, could n0t be Used for Co pa: ese
they controlled the movement speed of their subjects. The most noticeable di;°n because
between the children in the present study and adults is the am Cum of time Spentefence
1 versus Phase 3. The children spent substantially longer in Phase 1 than did the In Phase
Vvhile the adults spent longer in Phase 3 (the only exception Was erSChfeld, et all adults,
who reported a Phase 1 duration similar to that found for the children). On the w}: 1999.

Ole, the

93

_-_f

 

 

duratlon for Phase 2 was not substantially different between ch ildren and adults, As a

l-P

maximum ankle dorsiflexion ’ r eSPeCti Vel y) Occurred later for the children. One possible
cause for the greater amount of time the Children spent in Phase 1 (the flexiommomentum
phase) is that children may have more difficulty controlling the momentum Of the upper
body. Cahill, et a1 (1999) postulated this based on the fact that in their study total hip
displacement (in flexion) and peak hip flexion Velocity increased with increasing age.

This same result was found in the present study (see Tables 6 and 7). C ahill, et al. suggest
that this may be due to the proportionally greater mass of the head and trunk of children
compared to adults. On the other hand, the values for peak hip flexion velocity and peak
horizontal velocity of the body's center of gravity for the Older Children in the Present

study are similar to those found for adults. This Suggests th at CO 1 f 1’“ 0103mm“ may
ntro 0

not be the entire answer.

Another possibility is related to the fact that youn g Chi ldren have
longer torsos and shorter legs than adults (Malina & Bouchard, 1991 ). T proportionally
relatively more time is needed by the children to move the tI'Unk into Opt . erefore,
compared to the time needed to extend the legs. A third pOSSibih-ty is mo lmalposition
Hirschfeld, et a1. (1999), who had a similar Phase 1 duration as the preSeme mundane,

- . , Stud
that the later occurrence of seat-off in their study is due to the fact that .Y. argUCd
Seat-Off

determined kinetically using a force plate beneath the buttocks (as in th
e present
s
instead of kinematically. On the otherhand, Pai, Naughton, eta] (1994) tudy)
. also [1st

plate beneath the buttocks but found seat-off to occur at roughly 409' a force
0

94

 

101.7” Range of Motion
' ' '1) ts
Shown in Table 6 are the total ranges of motion at the ankle, knee. and [HP 101
t ' d for
reported for adults in various studies; the results of the present study are include

. ‘ tre orted
comparison. In comparison W1 th the adults in the (relatively few) studies tha p

. ang
OtiOfl at the ankle a smaller tang 1 motion at the knee, and a comparable I E
m ’

motion at the hip. The range of motion of the knee joint is almost entirely dependent 0:
the initial position of the knee joint while sitting and on how much the knee is extende
by the end of the STS. That the children in the present study had a smaller range 0f cment
motion at the knee is indicative of the fact that many of the Chi] dren be gan the mOV

t e

slightw flexed (see

F' ure 6) On the other hand many adults began the STS With their knees flexed more
1g .

900 close to seat-off, and then finished the STS with their kn 663 still

than 90° and fimShed in full “tettStOtt' That Children fin‘tSlled wi' th the knees slightly
kee the center of gravity slight] 1 .

flexed may be due to a need to P y owe;- Order to

' crease stability or to the fact that many of the children almost immedj

1n .

es

' d by the hildr andhips’ The
. kle 'oint experience c en c
greater range of motion at the an J 0111p d to the
d lts may be a result of increased postural sway due to a lack of POStUraI
a u

90mm]
(Shumway-Cook & Woollacott, 1985). The fact that the children in Group 3 (4t

5 years
f g6) had a greater ankle range of motion than the younger Children is n It i
0 a

nSiStent
'th this hypothesis, as Shumway-Cook and Woollacott suggest that this age is
\w

a
nsitional age in the development of postural control. Cahill, et a], (1999) Suggest
tra

ata

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lack of postural control may also be a cause of the greater vari ability in perfomance

evidenced by 4- and 5—year—ol d Children Compared to adults and 9- and IO-year—old

children. Interestingly, the 4 and 5-year-0]d Children in the present study had the smal lest

amount of variability in total movement time

In addition to the ranges of motion of various joints, many authors also report the
Pfiak hip flexion angle during the S TS (in fact, more studies report the peak hiP fleXion
angle than ranges of motion). The 1‘ eason for th is is that the maximum amount of hip
flexion indicates the amount of forward lean of the head and trunk (HAT) and iS related
to the most anterior position of the center of gravity, This latter position is also dependent
on the maximum amount of ankle dorsiflexion. These Values, as well as the time to Peak

- TabIe
hip flexion angle expressed as a percentage of total mOVemen t time are Show“ in

6. In comparison with the children in the study by Cam” et a1 Tame 6) the

~ (1999; see

subjects in the present study had similar peak hip flex‘bfl angles. In additlon the same
trend of 1ncreasing hip flexion angle With 1ncreasing age reported by Cab
11],

ct 31, Was
also found 1n the present study, but only for Groups I and 2 in relation t

I‘OUp 3 the
value for Group 2 was actually significantly less than that for Grou 1. W

possible explanations for the relationship between Groups

I and 2? on
fl 1 d is t at there 1'
real relationship between peak hip exion ang e an age, but that the 81' s n

fieam
differences are simply due to variability from one age t0 the next. EVid n
c

. e fOr this
explanation may be found in the range of peak h1p flex10n angles reported

1 .

the

for adult subjects (see Table 6). Another possibility, however, is related to

relationship between peak hip flexion angle and movement Speed: N amer

. . that (for the

same subject) the amount of hlp flexmn tends to decrease as movement Sp d
ee increa

ses

98

_-_f

 

& p a ' . a the m ller
C pozzo 2000; V nder Linden, 1994). It is POSSIble 1":me thatthes a
(Papa a , - - . -' ant] faster total
peak ' n angle for Group 2 is due in part to then‘ Signifg ‘9' .Y
mp flex“) (:3 . :ip flexion angle with
(see Iable 1). Likewise, the increase in peak 1”
movement time

ct that movement time
f und by Cahill, et al. may be due in part to the fa
increasing age O

150 increased (Lew movement Speed decl‘eased) with age to 47% of total
a resent ‘5de the time to peak hip flexion ranged 910‘“ 30 th
In the? p which is comparable to the times 169°“edm the literature {01' b0. (11611
movement nme’ Table 63' 111 addition, the time to peak hip flexion for cbfi

children and adults (see

1
O . .
v w a e b th in the Pmse“t StUdY and 1n the Singh, 1“, . Q 99)
' 0 \9

- 21 ed
ak hip fls xion was cons1stently r6 Cheq fore seat‘Ofi 000““
dy pe be
In the present stu

ables 5 and 6).1nteres tin

thi .
T gly, S ré Sult is in contrast With
(i.e, , in Phase 1', compare

t al. , 1 9g
dby Schenkman and colleagues (Ikeda, e
those ioun

) I
,

1; Riley, et al., 1991:.

which peak hip flexion
occurred slightly after seapoff .

Peak Joint Angular Velocities

The STS movement largely involves movement at the hip and

’02s.

e variable Of Interest thereforf? is the eJOIbts
122

' ' .On
a lesser extent, the ankle Jon’lt

. -nts involved, Particm
. nt at the 101 1 ’ V
attained during the moveme e . eloei

tudy the time for Group 1 was 'ust - .
- the resem S , . t1 dff Sigmfi
....o at... 6..., s. .
C310“? 2, whi e ne. . “meal“ 1 erence oup 2 is b‘ 13 qucStionab] or
tistically 51% 1 e
whethfl the Sta

. . O
Omechamcally signifivceaiicir’
99 .

 

a;

 

for both hip flexion (which occurs during the first part of the r1 6) Vemenuan d [up

extension (which occurs duri ng the latter part of the movement ) , as well as knee

extension (little knee flex‘on 0Ccurs once the movement is initi a ted) Also of interest are

the times at which these maxima are reached. Table ‘7 shows the" peak hip flexion, hip

extension, and knee extchSIOD velOCltles-as well as the times at vvhich these peaks

' f
occurred (as a percentage 0f movement tlrr“3)‘found in the Pfesemt studY'. data for some 0

these Variables reported by Cahill, et al' (1 999) for chi‘dfe“ and by four other aUthorS for

. ak
adults are also reported for companson- The most commonly tfiported variable W as 96

hip flexion velocity. The values found in the Present study for

' t
beak hip flexion veloCI V

were comparable to those reported by Cahill, et a1 . for childrQ

‘1 ‘ and by IKCda, et ai-
(1991) and Shepherd and Gentile (1994) for adults, although

the velocities found by the
author and by Cahili, et al. for the older children were greatQr
. than those found by Ikeda,
et a1. and Shepherd and Gentlle- ROCbYOCCk, 6t 81 - (1 994) r3130

1Ted 3 . .
velocity of 48°ls which is well below that found in any oth§r Peak hip flCXIOll
Stua
for peak hip and knee extenSion VCIOCihCS were also below 611' rePOITCd Value
Ose f0 8
U1) .
study and those reported by like“, Ct 81-. The l'eason for thi d 1 fl)
°W Value - ”resent
the fact that Roebroeck, et al. set the movement Speed at 23 Is

Cyc1es Per
to a movement speed of 2.3 s), slower than the natural" .

. , Vement [1'
other studies reported in Table 5 Wlth the exception of Kralj et
’ al- (1
. - 9
movement time of 3.3 s. LikeW1se, the relatively faster movem
em .

present study and reported by Cahill, et al. may be the reaso h

e the
studies were greater than those

100

 

 

 

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101

reported elsewhere? in addition, the same trend of increasing peak hip flexion velocity
with increasing age in children reported by Cahill, et al. was found in the present study.
However, whereas Cahill, et al. found the increase to be significant across all three age
groups, in the present study the differences between Group 1 and Group 2 and between
Group 1 and Group 3 were significant, but the difference between Group 2 and Group 3
was not.
As far as the timing of the peak velocities is concerned, only Roebroeck, et al.
(1994) and Schenkman, et al. (1990) reported values. The timing of the peak hip flexion
velocity in the present study corresponded well with that found in the study by
Roebroeck, et a], but was slightly later than that reported by Schenkman, et al.. On the
other hand, the timing of the peak hip and knee extension velocities in the present study
was comparable to those in the study by Schenkman, et al., but occurred later than that
reported by Roebroeck, et al.. As was the case for Schenkman, et al., the peak hip flexion
velocity occurred in Phase 1 and the peak hip and knee extension velocities occurred in

Phase 3.

Velocity, Momentum, and Kinetic Energy of the Whole-body Center of Gravity
Several studies on adults (see Table 8) have investigated the velocity profile of the
body's center of gravity (CG), typically looking at the horizontal (anterior-posterior) and

vertical components of the velocity of the CG. In addition, some authors have studied the

 

-———

2 However, it should be noted that in the present study the correlation between hip flexion velocity and
movement time was low (-. 174); this is unlike the correlations between hip extension velocity and
movement time, and between knee extension velocity and movement time, which were moderate (-.548 and

.510, respectively).

102

 

 

 

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linear momentum of the CG (Pai, Naughton, et al., 1994; Pai & Rogers, 1990a; Riley, et
al., 1991) and one study investigated the kinetic energy of the CG (Riley, et al. 1991).
There is, of course, a direct relationship among velocity, momentum, and kinetic energy.
Namely, momentum is equal to mass times velocity and kinetic energy is equal to one-
half the mass times velocity squared. Thus, as might be expected, the velocity,
momentum, and kinetic energy of the STS have similar patterns; it is only the magnitude
of each that varies. In fact, velocity allows for better comparison between subjects
because it is "normalized" by its very nature. That is to say, in order to normalize
momentum or kinetic energy we would typically divide by body mass, which leaves us
with velocity as a normalized momentum and one-half the velocity squared as a
normalized kinetic energy. For this reason, Table 8 (and Table C4 before it) reports only
the peak velocity of the CG (broken down into its horizontal and vertical components) for
the aforementioned studies, although the discussion below will include the momentum
and kinetic energy of the CG. The time taken to reach the peak horizontal and vertical
velocities, as well as the time to seat-off, is also shown in Table 8; the times are
expressed as a percentage of total movement time.

Compared to adults, several things can be noted about the velocity of the CG for
the children in the present study. First, the peak horizontal and vertical velocities of the
CG were substantially lower for the children versus the adults, with the exception of
those in the study by Roebroeck, et al. (1994). In this case the low velocities are probably
due to the slow movement times in that study (see above). In the present study, however,
the movement times were comparable to, and often faster than, the times in these adult

Studies. The lower peak velocities seen in the children may be related to the lack of

104

postural control noted earlier. Indeed, that peak horizontal and vertical velocities
increased with increasing age (although only Group 1 was significantly different than the
others; Groups 2 and 3 were not significantly different from each other) suggests that with
increasing motor development and postural control peak velocities can be increased as
well. Further evidence of this may be found in the increased joint velocities with
increasing age noted above.

Second, for the adults the peak vertical velocity was greater than the peak
horizontal velocity, whereas for the children the peak horizontal and vertical velocities
were close in magnitude to one another, with the peak vertical velocity being generally
slightly less than the peak horizontal velocity.

Third, the peak horizontal velocity occurred, on average, before the peak vertical
velocity for both the adults and the children. However, the peak horizontal and vertical
velocities tended to occur sooner for the adults versus the children, though it should be
noted that times for the children in Group 3 were similar to those reported by I-Iirschfeld,
et al. (1999) and Riley, et al. (1991). This timing may be related to the postural control
issue: If the children had more difficulty controlling their upper body movement they
might be expected to take longer to reach their peak horizontal velocity; this would in
turn delay the peak vertical velocity. The older children in Group 3 did in fact reach peak
horizontal velocity faster than the younger children, which would be expected if time to
peak horizontal velocity is related to motor development. Interestingly though, the time to
peak vertical velocity changed little from age group to age group. So perhaps although the

older Group 3 children could generate a greater horizontal velocity in a shorter amount of

105

time, they required alongel‘ braking period and thus the time to peak vertical velocity
remained almost unchanged.

Fourth, all of the adult studies found the peak horizontal velocity to occur before
seat-off, although how much before seat-off varied form one study to the next. For
instance, Riley, et al. (1991) found the peak horizontal velocity to occur very close to
seat-off (34 versus 36% of movement time), whereas in the study by Hirschfeld, et al.
(1999) it occurred at 41% of the movement time but seat-off not until 54%. The children
in the present study showed similar variability. The mean peak horizontal velocity for the
children in Group 1 actually occurred after seat-off, but this was largely due to Subject 5;
all of the other children reached peak horizontal velocity prior to seat-off (see Table C4).
On average the children in Groups 2 and 3 reached peak horizontal velocity before seat-
off (although for one subject in Group 2 it occurred after seat-off), but whereas for Group
2 as a whole peak horizontal velocity occurred close to seat-off (the same was true for
Group 1 as whole), it occurred substantially prior to seat-off for Group 3.

Finally, Riley, et al. (1991) found the peak vertical velocity to occur close to the
Phase 2-Phase 3 transition point. This was true for the present study for the children in
Groups 2 and 3, but the peak vertical velocity occurred well before the Phase 2-Phase 3
transition point for the children in Group 1. The Phase 2-Phase 3 transition point is the
point of maximum dorsiflexion of the ankle, which represents the most forward rotation
of the body over the ankle joint. It would fit that the youngest children who presumably
have the least postural control would still be rotating forward even as they reach peak

vertical velocity.

106

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'-
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As noted above, the velocity of the CG is directly related to the linear momentum
of the CG and its kinetic energy during the movement. Pai and colleagues (Pai, N aughton,
et al, 1994; Pai & Rogers, 1990a) and Riley, et al. (1991) have examined in detail the
linear momentum of the CG during the STS movement. The pattern of the horizontal and
vertical CG velocity curves (and thereby the momentum curves) found in the present
study (see Figure 11) was similar to that found by the above-named authors, differing
only in relative magnitude and the time between peaks. This relationship is one in which
the vertical velocity (and momentum) of the CG is at its lowest point close to the peak
horizontal velocity of the CG. Then as the horizontal velocity decreases the vertical
velocity increases until it reaches its peak. Riley, et al. found that the beginning of the
increase in the vertical velocity corresponded almost exactly with the peak horizontal
velocity. Pai and Rogers (1990a) found that the beginning of the rise in vertical velocity
always occurred close to the peak horizontal velocity, but at faster movement speeds
actually began before the peak horizontal velocity was reached. A similar result was
found in the present study. Figure 15 shows the horizontal and vertical velocity of the CG
versus time for two trials of different movement speeds. The upper graph (Figure 15a) is
of a relatively slower trial (movement speed equal to 1.6 3), while the lower graph (Figure
15b) is of a relatively faster trial (movement time equal to 0.9 s).

Riley, et al. (1991) also examined the resultant kinetic energy pattern of the CG
and found two kinetic energy peaks corresponding to the peak horizontal and peak
vertical velocities, respectively, and a relative kinetic energy minimum occurring between
these two peaks. Figure 16 shows a similar pattern for the trial shown in Figure 15a.

Riley, et al. suggest that the kinetic energy pattern and the relationship between the

107

Velocity (cm/s)

(8)

Velocity (cm/s)

(b)

40*

351

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Figure 15. Plot of the horizontal and vertical velocities of the whole body center of
gravity versus time for a relatively slow (a) and a relatively fast (b) trial.

108

 

 

 

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109

horizontal and vertical velocities points to a transfer of kinetic energy and momentum
from the upper body to the lower body during Phase 2 (aptly named the "momentum
transfer phase"). The similar results found in the present study suggest that the same is

true for children.

Ground Reaction Forces at the Buttocks and the Feet

Types of Forces

There are three types of forces involved in the STS movement: (1) a posteriorly-
directed, horizontal force from both the buttocks and the feet which generates a
propulsive impulse and forward momentum; (2) an anteriorly-directed, horizontal force
from the feet which generates a braking impulse to stop forward velocity; and (3) a
vertical force from the feet which generates a vertical impulse and vertical velocity (see
Figure 12). The type of pattern shown in Figure 12 has also been found for adults by
Hirschfeld, et al. (1999). Magnan, et al. (1996), and by Pai and colleagues (Pai,
Naughton, et al., 1994; Pai & Rogers, 1990). Whereas Hirschfield, et al. and Pai,
N aughton, et al. found the feet to have generated only a small, if not negligible,
propulsive impulse, in the present study the feet made a significant contribution (about
5% of body weight) to forward momentum. This result is, however, in agreement with
Magnan, et al. who also found a propulsive impulse of similar magnitude to have been
generated by the feet. It should also be mentioned when considering the horizontal forces
generated by the feet that if a subject moved immediately from the STS to walking (as
was the case for some of the younger children), and the stance leg was the one in contact

with the force platform, there was a transition from the braking impulse to a second

110

 

 

 

 

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111

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propulsive impulse (see, for example, Figure 17). This is consistent with the results

reported by Magnan, et al. for the "sit-to-walk" movement.

Horizontal Momentum and Horizontal Forces

Also of interest is the relationship between the horizontal velocity/momentum of
the body and the horizontal forces generated by the buttocks and the feet. In the STS
movement the maximum horizontal momentum is due to, and equal to, the propulsive
impulse (i.e., the area under the horizontal force vs. time curve). In the present study the
transition from a propulsive to a braking impulse occurred close to the time of peak
horizontal momentum (compare Figures 18a and b; in both figures the vertical bar
indicates the occurrence of the peak horizontal momentum). Pai and colleagues (Pai,
Naughton, et al., 1994; Pai & Rogers, 1990a) and Magnan, et al. (1996) found a similar
correspondence between the time at peak horizontal momentum and the time at the
transition from a propulsive to a braking impulse. Furthermore, in the present study the
peak braking force occurred close to seat-off (i.e., time zero; see Figure 18a), a result

which is also consistent with that found by Magnan, et al..

Amplitude of the Peak Vertical Ground Reaction F orce at the Feet

In the present study the peak vertical ground reaction force from the feet (GRFF)
was, on average, 150% of body weight for the entire group of subjects, but there was
considerable variation from subject to subject, and within subject from trial to trial. There
were not overly large differences in the peak vertical GRFF from age group to age group,

although it was significantly less for Group 1 vs. Group 2 (see Table C5). The values

112

 

 

 

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(b)

Figure 18. Plots for a single trial of (a) the resultant (i.e., of the buttocks and feet)
anterior-posterior force versus time and (b) the horizontal momentum of the center of
gravity versus time. The dotted vertical line indicates the time at peak horizontal
momentum.

113

 

 

 

 

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114

 

 

 

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115

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obtained in the current study for the peak vertical GRFF were consistently higher than
those found for other children by Cahill, et a1. (1999) and for adults by various authors
(see Table 9). One possible reason for the relatively high peak vertical GRFFs found in
the current study is the relatively fast movement times for subjects in the present study
versus those in other studies (see Table 5), the theory being that a faster movement would
require (or at least elicit) a greater peak vertical GRFF. This is similar to the argument
made above for the relationship between movement speed and peak joint angular
velocities. However, for the subjects in the present study the correlation between the peak
vertical GRFF and movement time, though significant, was only slight (r = -O.219). Thus
the higher peak vertical GRFFs in the current study may be due in part to the faster

movement times, but also to other unknown factors.

Timing of the Peak Vertical Ground Reaction Force at the Feet

In the current study the peak vertical ground reaction force from the feet (GRFF)
occurred, on average, at about 62% of total movement time for the entire group (see
Table 9). Thus the peak vertical force was reached approximately 9% of movement time,
or 100 ms, after seat-off. The older children in Group 3 reached their peak force
significantly faster than Groups 1 and 2 (53% vs. about 66% of movement time), and
their peak force occurred closer to seat-off (approximately 5% vs. 10% of movement time
closer). These results are similar to those obtained for children by Cahill, et al. (1999; see
Table 9): They found that the peak vertical force occurred at 124 ms after seat-off for
children 4.1-5.0 years of age (comparable to Group 3 subjects in the current study) and 85

ms after seat off for children 8.6-9.9 years of age. Thus the peak vertical force tended to

116

occur closer to seat-off with increasing age. It is interesting to note that overall, the
children in the present study tended to reach their peak vertical force closer to seat-off
than those of similar age in the study by Cahill, et al. Unfortunately, Cahill, et al. did not
report the timing of seat—off, so it is impossible to compare their results to those of the
present study based on percent of movement time. The timing of the peak vertical GRFF
reported by several authors for adults is also shown in Table 9. These results tend to
support the notion that the peak vertical force occurs sooner with increasing age, with
Millington, et al. (1992) and Vander Linden, et al. (1994) having reported a time-to-peak
of about 40% of movement time, substantially faster than those found in the present
study. Interestingly, though, Hirschfeld, et al. (1999) found a time-to-peak to be 51% of
movement time, not much different than that for the Group 3 subjects in the current
study.

The timing of the peak vertical force relative to seat-off is also of interest.
Millington, et a1. and Vander Linden, et al. both found the peak vertical force to have
occurred after seat-off as was the case in the present study and that by Cahill, et al., but
differed somewhat as to how long after seat off: 12% of movement time, or 240 ms,
reported by Millington, et al.; and 6% of movement time, or 86 ms, reported by Vander
Linden, et al.. On the hand, Hirschfeld, et al. found the peak vertical force to have
occurred some 3% of movement time (45 ms) before seat-off. Why does this result differ
from those of Millington, et al. and Vander Linden, et al.? One possibility has to do with
the definition of seat-off: Neither Millington, et al. or Vander Linden, et al. measured the
actual moment at which the buttocks lost contact with the seat, but used other methods to

estimate the moment of seat-off. Thus Hirschfeld, et al. would likely argue (see below in

117

 

 

the discussion of the location of the center of gravity relative to the center of pressure at
the moment of seat-off) that in the aforementioned studies the actual seat-off occurred
later than that reported, and thus the time to peak vertical GRFF would occur close to or
after the actual seat-off. On the other hand, in the current study the actual moment that the
buttocks lost contact with the seat was measured via the force plate on the seat, and yet
the time to peak vertical GRFF still occurred after seat-off. It is not clear, then, whether
the result of Hirschfeld, et al. is simply an anomaly or whether the timing of the peak
vertical GRFF oCcurs closer and closer to seat—off with increasing age, to the point that in

adulthood the peak vertical GRFF may occur at, or even before, seat-off.

Location of the Center of Gravity Relative to the Center of Pressure at Seat-ofi

There is some debate in the literature as to the location of the body's center of
gravity relative to the center of pressure at the feet at the time of seat-off (i.e., the point
when double support-the buttocks and feet-shifts to single support-the feet alone). The
significance of the relative location of the center of gravity has to do with the degree of
stability of the STS performer and the strategies that underlie the movement pattern of the
upper body in the STS. As discussed in the Review of Literature, two primary strategies
have been suggested (Berger, et al., 1988; Hughes, et al., 1994; Schenkman, et a1. 1990):
(1) "momentum transfer," in which hip and trunk flexion are used to generate momentum
which can then be transferred to the whole body, and (2) "stabilization," in which trunk
flexion is not used to generate momentum, but rather to position the center of gravity of
the body closer to the base of support at the time of seat-off. In the momentum transfer

strategy the center of gravity would be expected to lag behind the center of pressure, and

118

 

 

the body would be expected to have appreciable forward velocity, at the time of seat-off.
In the stabilization strategy, on the other hand, the center of gravity would be expected to
be over the base of support and close to the center of pressure at the time of seat-off. In
addition, the forward velocity of the body would be expected to be approaching zero at
seat-off. As noted, these two strategies are not mutually exclusive: forward flexion might
act both to move the center of gravity closer to the base of support under the feet as well
as generate momentum, but even in this case the center of gravity would still be expected
to lag behind (Riley, et al., 1991).

Riley, et al. (1991), preceded by Schenkman, et al. (1990), found that at the time
of seat-off the center of gravity was located approximately 7 cm behind the center of
pressure. Thus at the time of seat-off the subjects were in an inherently unstable position.
In addition, they found that the horizontal velocity of the upper body actually reached its
peak at seat-off. These results led Riley, et al. to conclude that the subjects used the upper
body to generate forward momentum, as well as possibly to position the center of gravity
more favorably at seat-off. However, Hirschfeld, et al. (1996) found the center of gravity
to be over the center of pressure at seat-off and therefore argue that the stabilization
strategy stated above is being used and that the body is in a state of stable equilibrium at
the time of seat-off. They suggest that the results obtained by Riley, et al. and
Schenkman, et al. are due to the fact that these authors define seat-off as the point at
which the vertical reaction force at the feet begins to increase (as opposed to noting the
actual point of the buttocks leaving the seat), an event that occurred about 250 ms before
seat-off in the study by Hirschfeld, et al. (and about 175 ms before seat-off in the present

study). Thus Hirschfeld, et al. argued that if one adjusts Riley, et al. and Schenkman, et

119

 

al.'s results accordingly, the center of gravity is located over the center of pressure at seat-
off. This may be true in the case of Riley, et al. and Schenkman, et al., but it ignores other
studies that did define seat-off as the moment the buttocks left the seat and yet found the
center of gravity to be located posterior to the center of pressure at seat—off: e.g., Kelley,
et al. (1976); Murray, et al. (1967); Pai, Naughton, et a1. (1994). In the present study the
center of gravity was also located, on average, posterior to the center of pressure at the
moment of seat-off (about 5 cm). What Hirschfeld, et al. failed to consider is that both
strategies, or a combination of them, may be viable, as evidenced in the study by Hughes,
et al. (1994). In other words, for what ever reason the subjects in the study by Hirschfeld,
et al. may have been using the stabilization strategy, whereas in studies in which the
center of gravity was found to lag behind the center of pressure at the moment of seat-off
the momentum transfer strategy or a combination of the two strategies may have been

used.

Joint Moments
Another variable of interest is the peak joint (extension) moment experienced at
the hip and knee joint during the execution of the STS movement.3 Kotake, et al. ( 1993)
calculated the theoretical minimum moments required for adults to execute the STS
movement, and found the minimum hip and knee joint moments required to be 12111.7
and 15601.7, respectively. However, the study by Doorensbosch, et al. (1994) and the

present study have found actual peak hip and knee joint moments that are less than the

 

3 In the discussion which follows it is important to recall that the joint moments have been normalized by
dividing by the subject's body weight in newtons, multiplying by the subject's height in meters, and
multiplying by 100.

120

 

 

 

minimum theoretical values calculated by Kotake, et al. (see Table 9). The reason for
these discrepancies is not clear, although it may relate to the model used by Kotake, et al.
and its possible lack of relevance to children. Nevertheless, it is clear that the subjects in
the present study had no difficulty in completing the STS movement despite
comparatively low peak joint moments.

The magnitude of the mean peak hip and knee joint moments reported in the
literature varies greatly, ranging from 10.8 to 39.8 for the normalized peak hip joint
moment and 14.4 to 47.0 for the normalized peak knee joint moment (see Table 9). In the
present study a great deal of variation existed as well, with the mean normalized peak
moments for each subject ranging from 5.8 to 50.6 for the hip joint and 2.8 to 18.8 for the
knee joint (see Table C5). Whereas the peak hip joint moments in the present study were
similar in magnitude to those reported in the literature (although the Group 1 and 2
subjects tended to be at the lower end of the range), the peak knee joint moments tended
to be lower than the values reported in the literature. This result is somewhat unexpected,
as the peak ground reaction forces at the feet and the peak knee extension velocities for
the subjects in the present study were greater, on the whole, than those reported in the
literature (see Tables 12 and 14). On the other hand, the peak velocity of the center of
gravity of the subjects in the present study tended to be lower than that reported in the
literature (see Table 8). It may well be that one or more of the variables that determines
the joint moment (e. g., segmental linear acceleration, angular acceleration) were lower for
the subjects in the present study compared to those reported in the literature. Another
possibility is related to body proportions: Compared to adults, children tend to have

proportionally longer torsos and shorter legs (Malina & Bouchard, 1991), which could

121

 

 

mean that in rotating about the knee children have a relatively smaller moment of inertia
(I) and therefore a smaller moment (since M = Ia). A third possibility is that for children
weight may have a greater impact than height, so that normalizing by dividing by body
weight and multiplying by height results in a smaller relative moment for the children
compared to the adults (of course this would apply to the hip joint moment as well).

The magnitude of the peak hip joint moment relative to the magnitude of the peak
knee joint moment also differed in the present study compared to many previous studies.
Namely, in nearly every case in the present study the peak hip joint moment was greater
than that of the knee joint, whereas many studies (Doorenbosch, et al., 1994; Ikeda, et al.,
1991; Pai & Rogers, 1991; Roebroeck, et al., 1994) found the peak knee joint moment to
be the greater of the two (see Table 9). The only exception was the study by Shepherd and
Gentile (1994), who found the peak hip joint moment to be about twice that of the peak
knee joint moment. However, as discussed in the Review of Literature, many of the
studies involving subjects with movement limitations (e. g., older adults and obese
individuals) employed strategies (the stabilization and "combined" strategies; Hughes, et
al., 1994) that involved less hip flexion and a smaller hip moment, but a greater knee
moment. It may be that the subjects in some of the previously-mentioned studies
employed a more combined type strategy. The subjects in the present study, however,
seemed to use the "momentum transfer strategy" (Hughes, et al.) as evidenced by the
relatively large amount of hip flexion and relatively high hip flexion velocity (see Tables
11 and 12), and by the greater magnitude of the peak hip joint moment versus the knee

joint moment that they experienced.

122

 

Strategies Used by Children in Pen‘orming the Sit-to-Stand Movement

As noted in the Review of Literature, Cahill, et al. (1999) suggested that the
increasing hip flexion and peak hip flexion velocity with increasing age seen in their
subjects is due to the gradual development of greater postural and motor control. This
could possibly mean that the younger children, who have less postural control and
balance, employ more of a stabilization strategy and the older children, who have greater
postural control and balance, use more of a momentum transfer strategy (Hughes, et al.,
1994; McMillan, 1998). Unfortunately, Cahill, et a1. did not measure (or at least did not
report) moments about the hip and knee joints or the location of the center of gravity
relative to the center of pressure at seat-off. Both of these variables are additional factors

as to whether a stabilization or momentum transfer strategy (or a combination) is being
used (Hughes, et al.). In the present study, however, these variables were measured, in
addition to the amount of hip flexion and the peak hip flexion velocity.

If the subjects in the present study are taken as a whole and compared to results
for younger adults as reported in the literature, the following may be noted: the children
in the present study had shorter movement times, comparable ranges of motion at the hip
joint, and comparable or greater hip flexion velocities than younger adults. Furthermore,
the subjects in the present study had greater hip joint moments than knee joint moments
and the center of gravity was located behind the center of pressure at seat—off. These
results, together with the fact that the momentum profile of the center of gravity was
similar to that reported by Riley, et al. (1991) for adults (see Figure 11), would tend to
suggest that, as a whole, the children in the present study favor a momentum transfer

strategy, or at the very least, a combination of the two strategies (Hughes, et al., 1994).

123

 

 

E4...

 

Comparing the above-named variables between the age groups in the present
study, the following may be noted: Groups 1 and 3 had similar movement times, but
Group 2 had faster movement times than the other groups; Groups 1 and 2 had similar
ranges of motion at the hip, but Group 3 had a greater range of motion at the hip than the
other groups; peak hip flexion velocity tended to increase with increasing age; peak hip
and knee joint moments tended to increase with increasing age, but the peak hip joint
moment was consistently greater than the knee joint moment; and the center of gravity
was consistently located behind the center of pressure at seat-off.4 These results show no
clear developmental trend from a stabilization strategy to a momentum transfer strategy
with increasing age. This is opposed to McMillan (1998) who found that at the younger
ages children typically had a forward-up movement pattern (similar to the stabilization
strategy), while the majority of the children had switched to a diagonal-up movement
pattern (similar to the momentum transfer strategy) by 24 months of age. However, it is
possible that the younger children in the present study used more of a combined strategy
versus the strict momentum transfer strategy used by the older children. This is suggested
by the fact that the peak hip flexion velocities of the youngest children were slightly
lower than the values reported in the literature (which would be characteristic of the
stabilization strategy) yet their center of gravity tended to be located behind the center of
pressure at seat-off (which would be characteristic of the momentum transfer strategy),

and by the fact that hip range of motion and peak hip flexion velocity increased with

 

4 Out of the 120 trials performed by all of the subjects, only 18 (15%) had the center of gravity located at or
in front of the center of pressure at the time of seat-off. Of these 18 "positive" trials, 8 were distributed
among 4 of the 5 subjects in Group 1, 6 were distributed among 2 of the 3 subjects in Group 2, and 4 were
distributed among 2 of the 4 subjects in Group 3. Thus there was no clear age trend.

124

 

 

increasing age. It should be kept in mind that the stabilization and momentum transfer
strategies likely represent two ends of a continuum, and that a combined strategy could
fall anywhere between the two (Hughes, et al., 1994). Thus the younger children are using
a combined strategy which likely becomes more and more "momentum-transfer-like"

with increasing age.

125

 

 

 

SUNIMARY AND RECOMMENDATIONS

The specific aims of the present study were firstly to assess as broadly as possible
the kinematics and kinetics of the sit-to-stand movement in young children (especially as
it compares to younger adults), and secondly to compare the biomechanics of the sit-to-
stand movement among children of different ages in order to determine if any age-related
differences might exist. In order to achieve the first aim, the following kinematic and
kinetic variables were investigated: movement and phase times (Figure 5 and Table C1);
the pattern of joint angular motion during the movement (Figure 6); ranges of motion at
the hip, knee, and ankle joints (Figure 7 and Table C2); peak hip flexion angle and the
time to reach this peak (Figure 8 and Table C2); peak hip flexion, hip extension, and knee
extension velocities and the time at which each of these peaks occurred (Figure 9 and
Table C3); the peak horizontal and vertical velocities of the center of gravity and the time
at which each of these peaks occurred (Figure 10 and Table C4); the pattern of the
horizontal and vertical velocities of the center of gravity during the movement (Figure
11); the kinetic energy pattern of the center of gravity during the movement (Figure 16);
the pattern of the anterior-posterior and vertical ground reaction forces at the buttocks and
at the feet during the movement (Figure 12); the peak vertical ground reaction force at the
feet and the time at which this peak occurred (Figure 13 and Table C5); the peak hip and
knee joint moments (Figure 14 and Table C5); and the location of the center of gravity
relative to the center of pressure at the time of seat-off.

The results of this study indicate that the overall pattern of the STS movement is

well-developed even in the youngest children and is similar to that seen in adults. These

126

 

similarities include the overall joint motion pattern and the pattern of forces at the
buttocks and the feet. As far as the overall joint motion is concerned, the STS movement
begins with hip flexion and ankle dorsiflexion which continues until after seat-off, when
flexion changes to extension, and hip and knee extension and ankle plantar flexion occur.
Concerning the forces at the buttocks and feet, the STS movement is initiated by a
posteriorly-directed, propulsive horizontal force from the buttocks followed shortly by a
(relatively-small) posteriorly-directed force from the feet. At about the same time as the
posterior force from the feet is initiated, there begins a period of loading (vertical force) at
the buttocks and unloading (vertical force) at the feet. This is followed by loading at the
feet which generates the propulsive vertical force for extension of the body, and the onset
of an anteriorly-directed, braking horizontal force from the feet which acts to check the
forward momentum of the body.

Although the overall pattern of the STS movement is similar for children in the
present study to that reported for adults, differences did exist for some variables. First, the
children had faster movement times than those reported in the literature for adults. It was
hypothesized that this could be due to the adults performing the STS task in a more self-
conscious, and therefore slower, way, or to the children rising as quickly as possible to
move toward the comfort of their waiting parents. Another difference was that the
children had a greater range of motion at the ankle than the adults, which, it was
suggested, could be a result of increased postural sway due to a lack of postural control. A
third difference was that the peak hip flexion velocities of the children tended to be
greater than those reported for adults, and is perhaps related to the faster movement times

of the children. Fourth, the peak vertical and horizontal velocities of the center of gravity

127

 

 

 

were lower for the children compared to those reported for adults, and these velocities
tended to occur later for the children. These results may also be related to a lack of
postural control on the part of the children, which causes them to take longer to reach
peak velocity and to attain a lower peak velocity. A fifth difference was that the
normalized peak vertical ground reaction force from the feet was substantially higher for
the children compared to those reported in the literature for adults, and it tended to occur
later for the children. The reason for the greater peak force seen in the children is not
entirely clear, but it was proposed that the faster movement times of the children might be
a contributing factor. The longer time taken to reach the peak vertical force seen in the
children could possibly be due to the lack of postural control cited earlier. Finally, the
children had lower normalized peak knee joint moments than those reported for adults,
which was unexpected due to the greater peak vertical ground reaction force and greater
peak knee extension velocity experienced by the children, but which may be due to
differences in body proportions between children and adults.

On the whole, most of the differences cited can likely be attributed to the faster
movement times of the children and/or a relative lack of postural control and balance in
the children compared to adults. It should be remembered, however, that even the
youngest children did not employ a solely stabilization strategy (which would tend to be
seen in individuals with a lack of balance and postural control), but had many elements of
the momentum transfer strategy, and thus their strategy would be categorized as a
combined strategy. But, as noted in the Discussion section, the strategy one uses to
perform the STS task is on a continuum. Therefore it is likely that the children (especially

the younger children) utilize a combined strategy because they lack some of the balance

128

 

 

and postural control of adults, but as their balance and motor control improve they move
more toward the momentum-transfer-end of the continuum. This seems to be borne out
by the fact that the oldest children in the present study had the greatest range of motion at
the hip and that peak hip flexion velocity tended to increase with increasing age. The
same trend of increasing hip flexion and hip flexion velocity with increasing age was seen
in the children in the study by Cahill, et al. (1999), and those authors reached a similar
conclusion.

The results of this study point the way toward two future research areas on the
STS movement in children. First, there is a good deal of research on the effects of chair
design (e.g., seat height, backrest) on the mechanics of the STS movement in adults. Thus
a logical avenue for future research would be to study the effects of these variables on
children. Not only would this type of research benefit physical therapists and other
rehabilitation specialists, but it would also help the furniture industry in designing and
manufacturing chairs appropriate for children. Second, while the normative data on the
STS movement in able-bodied children presented in this study will hopefully aid
rehabilitation specialists in working with children with disabilities, specific research
needs to be conducted on the performance of the STS movement in children with
disabilities. Having a knowledge of how children with disabilities perform the STS
movement compared to able-bodied children would enable physical therapists and others
rehabilitation specialists to perform their work more effectively.

If the specific aims of the present study were to analyze the kinematics and
kinetics of the sit-to-stand movement in young children and to determine if any age-

related differences exist in the performance of this movement, the more overarching goal

129

 

 

of this study was to provide much-needed fundamental information on the mechanics of
the sit-to-stand movement in able-bodied children that would be of help to physical
therapists and other rehabilitation specialists in the rehabilitation of injured children and

children with disabilities. Only time will tell if this study achieves that goal.

130

 

 

 

 

 

APPENDIX A: INFORMED CONSENT FORM

131

 

INFORMED WRITTEN CONSENT FORM

This consent form is intended for parents/guardians whose children are involved in a study of the mechanics
of the sit-to-stand movement and its development in young children which is being conducted by Eugene
W. Brown and David M. Wisner of the Department of Kinesiology at Michigan State University.

The purpose of this study is to use video cameras and force platforms (special metal plates which measure
the forces experienced by the body) to determine the mechanical way in which young children rise from a
seated position to a standing position, and the developmental changes that occur in this movement pattern.

While your participation in this study does not guarantee any beneficial results for you and/or your child,
the study will have benefits for certain segments of society. Namely, this study will provide information on
standing movements in able-bodied young children, so that physicians and physical therapists will be better
able to help children with disabilities and/or delayed physical development regain the ability to perform this
movement and thus regain mobility, which is critical for independent living.

Your child's involvement in this study will include some or all of the following:

( l) His/her weight and height will be measured.

(2) Reflective markers may be placed on the joints of his/her body, so that they can be seen more clearly on
video tape.

(3) He/she will be asked to stand up from a seated position on a bench (adjusted to the appropriate height)
approximately 20 times while the movement is videotaped.

(4) He/she will be asked to perform the movement barefoot.

(5) You may be asked to model the movement for him/her and to verbally encourage him/her as he/she
performs the movement.

The entire process should take approximately 60 minutes of your and your child’s time.

As sitting and standing are daily activities that your child engages in, this study does not pose any unusual
risk of injury or illness.

Your child’s name will not be associated with any publication and/or presentation of the information
collected in this study, and that only the two investigators (Eugene Brown and David Wisner) will know the
names of the participants in this study. However, the information may be used (with no names associated
with it) for demonstration, instruction, and/or study.

Your and your child’s participation in this study is voluntary and you will not be compensated monetarily
for your time. Note, however, that you and your child are free to discontinue your participation in this study

at any time, no questions asked, without penalty.

If you have further questions about the study, you may contact either of the two investigators at any time:

Eugene W. Brown David M. Wisner
353-6491 432-4073
ewbrown @msu.edu wisnerda@msu.edu

 

 

If you have further questions about your and your child’s role as a research subject, you may contact:
David E. Wright

Chair, University Committee on Research Involving Human Subjects
355-2180

132

I (please print name) have read the preceding information and understand
the procedures involved in this study, as well as its risks and benefits. I hereby agree to voluntarily
participate, and allow my child (please print name) to voluntarily
participate in this research study.

 

 

Signature of Parent/Guardian Date

133

APPENDIX B: QBASIC PROGRAM INVDYN

134

PROGRAM INVDYN

DECLARE SUB Invdynamics (footmassl. shnkmass!, thimassl, toexl, toeyl, anklex!, ankleyl, kneexl,
kneeyl, hipxl, hipyl, cmfootx!, cmfooty!, cmshnkxl, cmshnky!, cmthixl, cmthiyl, ifoot!, ishank!,
ithighl, ftaccxl, ftaccy!, shkaccx!, shkaccyl, thiaccxl, thiaccyl, grfvertl, grfhorl, xmoml, alphaftl,
alphashkl, alphathil, fankxl, fanky!, ankmoml, fl<neex!, fkneeyl, kneemom!, fhipxl, fhipy!, hipmom!)

DECLARE SUB Accel (toeaccxl, toeaccyl, ankaccxl, ankaccyl, kneeaccxl, kneeaccyl, hipaccxl, hipaccyl,
ftaccxl, ftaccy!, shkaccx!, shkaccyl, thiaccxl, thiaccy!)

DECLARE SUB MomIn (footmassl, shnkmassl, thimassl, footlenl, shnklenl, thilenl, ifoot!, ishank!, ithigh!)

DECLARE SUB SegLen (toex!, toeyl, anklex!, ankleyl, kneexl, kneeyl, hipxl, hipyl, footlenl, shnklenl,
thilen!)

DECLARE FUNCTION Con! (grfvertl, xmom!)

DECLARE SUB CoMpro (toex, toey, anklex, ankley, kneex, kneey, hipx, hipy, cmfootx, cmfooty,
cmshnkx, cmshnky, cmthix, cmthiy)

DECLARE SUB Masspro (wt, bodymass, footmass, shnkmass, thimass)

OPEN "C:\Basic\jtforce.dat" FOR INPUT AS #1

OPEN "C:\Basic\invdyn.txt" FOR OUTPUT AS #2

CLS

first = 0

oldid = 0

oldtrial$ = ”0"

DO UNTIL EOF( 1)

INPUT #1, id, trial$, time, wt, toex, toey, anklex, ankley, kneex, kneey, hipx, hipy, grfvert, grfhor,
xmom, toeaccx, toeaccy, ankaccx, ankaccy, kneeaccx, kneeaccy, hipaccx, hipaccy, alphaft,
alphashk, alphathi

IF id = oldid AND trial$ = oldtrial$ THEN

 

first = 0
ELSE
first: 1
END IF
IF first = 1 THEN
PRINT #2, ""
PRINT #2, ""

PRINT #2, "JOINT FORCES AND MOMENTS FOR SUBJECT"; id; "TRIAL"; " "; trial$
PRINT #2, TAB(4); "TIME"; TAB(12); "FANKX"; TAB(22); "FANKY"; TAB(32);
"ANKMOM"; TAB(42); "FKNEEX"; TAB(52); "FKNEEY"; TAB(62); "KNEEMOM";
TAB(72); "FI-IIPX"; TAB(82); "FI-IIPY"; TAB(92); "HIPMOM"
END IF

CALL Masspro(wt, bodymass, footmass, shnkmass, thimass)

CALL CoMpro(toex, toey, anklex, ankley, kneex, kneey, hipx, hipy, cmfootx, cmfooty, cmshnkx,
cmshnky, cmthix, cmthiy)

CALL SegLen(toex, toey, anklex, ankley, kneex, kneey, hipx, hipy, footlen, shnklen, thilen)

CALL Momln(footmass, shnkmass, thimass, footlen, shnklen, thilen, ifoot, ishank, ithigh)

CALL Accel(toeaccx, toeaccy, ankaccx, ankaccy, kneeaccx, kneeaccy, hipaccx, hipaccy, ftaccx, ftaccy,
shkaccx, shkaccy, thiaccx, thiaccy)

CALL Invdynamics(footmass, shnkmass, thimass, toex, toey, anklex, ankley, kneex, kneey, hipx, hipy,
cmfootx, cmfooty, cmshnkx, cmshnky, cmthix, cmthiy, ifoot, ishank, ithigh, ftaccx, ftaccy,
shkaccx, shkaccy, thiaccx, thiaccy, grfvert, grfhor, xmom, alphaft, alphashk, alphathi, fankx, fanky,
ankmom, fkneex, fkneey, kneemom, fhipx, fhipy, hipmom)

135

PRINT #2, USING "."#######; time; TAB(10); fankx; TAB(ZO); fanky; TAB(30); ankmom;
TAB(40); fkneex; TAB(SO); fkneey; TAB(60); kneemom; TAB(70); fhipx; TAB(80); fhipy;
TAB(90); hipmom

oldid = id
oldtrial$ = trial$
LOOP

PRINT "End of File Reached"
CLOSE #1

CLOSE #2

END

SUB Masspro (wt, bodymass, footmass, shnkmass, thimass)
bodymass = wt / 9.81

footmass = .0145 * bodymass

shnkmass = .0465 * bodymass

thimass = .1 * bodymass

END SUB

SUB CoMpro (toex, toey, anklex, ankley, kneex, kneey, hipx, hipy, cmfootx, cmfooty, cmshnkx,
cmshnky, cmthix, cmthiy)

cmfootx = .5 "‘ (toex - anklex) + anklex

cmfooty = .5 * (ankley - toey) + toey

cmshnkx = .433 * (anklex - kneex) + kneex

cmshnky = kneey - .433 * (kneey - ankley)

cmthix = .433 * (kneex - hipx) + hipx

cmthiy = hipy - .433 * (hipy - kneey)

END SUB

SUB SegLen (toex, toey, anklex, ankley, kneex, kneey, hipx, hipy, footlen, shnklen, thilen)
footlen = SQR((anklex - toex) A 2 + (ankley - toey) A 2)

shnklen = SQR((kneex - anklex) A 2 + (kneey - ankley) A 2)

thilen = SQR((hipx - kneex) A 2 + (hipy - kneey) A 2)

END SUB

SUB MomIn (footmass, shnkmass, thimass, footlen, shnklen, thilen, ifoot, ishank, ithigh)
ifoot = footmass * (footlen/ 100 * .475) A 2

ishank = shnkmass * (shnklen/ 100 * .302) A 2

ithigh = thimass * (thilen/ 100 * .323) A 2

END SUB

SUB Accel (toeaccx, toeaccy, ankaccx, ankaccy, kneeaccx, kneeaccy, hipaccx, hipaccy, ftaccx, ftaccy,
shkaccx, shkaccy, thiaccx, thiaccy)

ftaccx = .5 * (toeaccx - ankaccx) + ankaccx

ftaccy = .5 "‘ (ankaccy - toeaccy) + ankaccy

shkaccx = .433 * (ankaccx - kneeaccx) + kneeaccx

shkaccy = kneeaccy - .433 * (kneeaccy - ankaccy)

thiaccx = .433 * (kneeaccx - hipaccx) + hipaccx

thiaccy = hipaccy - .433 * (hipaccy - kneeaccy)

END SUB

136

FUNCTION Con (grfvert, xmom)
cpfp = -xmom / grfvert

cpcoord = .625 - cpfp

Con = cpcoord * 100

END FUNCTION

SUB Invdynamics (footmass, shnkmass, thimass, toex, toey, anklex, ankley, kneex, kneey, hipx, hipy,
cmfootx, cmfooty, cmshnkx, cmshnky, cmthix, cmthiy, ifoot, ishank, ithigh, ftaccx, ftaccy, shkaccx,
shkaccy, thiaccx, thiaccy, grfvert, grfhor, xmom, alphaft, alphashk, alphathi, fankx, fanky, ankmom,
fkneex, fkneey, kneemom, fhipx, fhipy, hipmom)

pi = 3.1415927#

fankx = footmass * ftaccx! 100 + grfhor

fanky = footmass * 9.81 + footmass * ftaccy/ 100 - grfvert

ankmom = ifoot * (alphaft * pi / 180) + fankx * ((ankley - cmfooty)/ 100) + fanky * ((cmfootx - anklex)/
100) + grfvert * ((cmfootx - Con(grfvert, xmom))l 100) - grfhor * cmfooty/ 100

fltneex = shnkmass * shkaccx/ 100 - fankx

fkneey = shnkmass * shaccy/ 100 - fanky

kneemom = ishank * (alphashk * pi / 180) - ankmom + fltneex * ((kneey - cmshnky)/ 100) + fkneey *
((cmshnkx - kneex)/ 100) - fankx * ((cmshnky - ankley)/ 100) - fanky * ((anklex - cmshnkx)/ 100)

fhipx = thimass * thiaccx/ 100 - fkneex

fhipy = thimass * thiaccy/ 100 - fkneey

hipmom = ithigh * (alphathi * pi / 180) - kneemom + fhipx * ((hipy - cmthiy)/ 100) + fhipy * ((cmthix -

hipx)/ 100) - fkneex * ((cmthiy - kneey)/ 100) - fkneey * ((kneex - cmthix)/ 100)

END SUB

137

APPENDIX C: MEAN DATA FOR ALL SUBJECTS

138

 

 

 

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REFERENCES

144

 

REFERENCES

Alexander, N .B., Galecki, A.T., Nyquist, L.V., Hofmeyer, M.R., Grunawalt, J .C.,
Grenier, M.L., Medell, J .L. (2000). Chair and bed rise performance in ADL-impaired
congregate housing residents. Journal of the American Geriatrics Society, 48, 526-

533.

Alexander, N.B., Koester, D.J., Grunawaldt, J.A. (1996). Chair design affects how older
adults rise from a chair. Journal of the American Geriatrics Society, 44, 356-362.

Alexander, N.B., Schultz, A.B., & Warwick, D.N. (1991). Rising from a chair: Effects of
age and functional ability on performance biomechanics. Journal of Gerontology, 46,
M91-M98.

Anglin, C., & Wyss, UP. (2000). Arm motion and load analysis of sit-to-stand, stand-to-
sit, cane walking lifting. Clinical Biomechanics, 15, 441-448.

Arborelius, U.P., Wretenberg, P., & Lindberg, F. (1992). The effects of arrmrests and seat
heights on lower-limb joint load and muscular activity during sitting and rising.
Ergonomics, 35, 1377-1391.

Baer, G.D., & Ashbum, A.M. (1995). Trunk movements in older subjects during sit-to-
stand. Archives of Physical Medicine and Rehabilitation, 76, 844-849.

Bayley, N. (1969). Manual for the Bayley Scales of Infant Development. New York: The
Psychological Corporation.

Berger, R.A., Riley, P.O., Mann, R.W., & Hodge, WA. (1988). Total body dynamics in
ascending stairs and rising from a chair following total knee arthroplasty.
Transactions of the 34'” Annual Meeting of the Orthopaedic Research Society, 13,
542.

Borges, O. (1989). Isometric and isokinetic knee extension and knee flexion torque in
men and women aged 20-70. Scandinavian Journal of Rehabilitation Medicine, 21,
45-53.

Brugnolotti, J. (1992). A pilot study of kinematic changes during the normal development
of sit to stand. Unpublished master's thesis, University of North Carolina, Chapel Hill,
NC.

Burdett, R.G., Habasevich, R., Pisciotta, J., & Simon, SR. (1985). Biomechanical
comparison of rising from two types of chairs. Physical Therapy, 65, 1177-1183.

145

 

 

Cahill, B.M., Carr, J H & Adams, R. (1999). Inter-segmental co-ordination in sit-to-
stand: an age cross-sectional study. Physiotherapy Research International, 4, 12-27.

Carr, J.H., & Gentile, A.M. (1994). The effect of arm movement on the biomechanics of
standing up. Human Movement Science, 13, 175-193.

Cheng, P.-T., Liaw, M.-Y., Wong, M.-K., Tang, F.-T., Lee, M.-Y., & Lin, P.-S. (1998).
The sit-to-stand movement in stroke patients and its correlation with falling. Archives
of Physical Medicine and Rehabilitation, 79, 1043-1046.

Clauser, C.E., McConville, J.T., & Young, J.W. (1969). Weight, volume and center of
mass of segments of the human body. AMRL Technical Report, Wright-Patterson Air
Force Base, Dayton, OH.

Coghlin, S.S., & McFadyen, 8.]. (1994). Transfer strategies used to rise from a chair in
normal and low back pain subjects. Clinical Biomechanics, 9, 85-92.

Dawson, D., Hendershot, G, & Fulton, J. (1987). Aging in the eighties: Functional
limitations of individuals age 65 and over. Advance Data From Vita] and Health
Statistics 133, DHHS-PHS-87-1250, Public Health Service, Hyattsville, MD.

Dempster, W.T. (1955). Space requirements of the seated operator. WADC Technical
Report 55-159, Wright-Patterson Air Force Base, Dayton, OH.

Doorenbosch, C.A., Harlaar, J ., Roebroeck, M.E., & Lankhorst, GJ. (1994). Two
strategies of transferring from sit-to—stand; the activation of monoarticular and
biarticular muscles. Journal of Biomechanics, 27, 1299-1307.

Ellis, M.I., Seedhom, B.B., & Wright, V. (1984). Forces in the knee joint whilst rising
from a seated position. Journal of Biomedical Engineering, 6, 113-120.

Engardt, M., & Olsson, E. (1992). Body weight-bearing while rising and sitting down in
patients with stroke. Scandinavian Journal of Rehabilitation Medicine, 24, 67-74.

Fleckenstein, S.J., Kirby, R.L., & MacLeod, DA. (1988). Effect of limited knee-flexion
range on peak hip moments of force while transferring from sitting to standing.
Journal of Biomechanics, 21, 915-918.

Francis, ED. (1987). Description of the sit-to-stand motion in children and young adults:
Hypothesis of developmental sequences. Unpublished master’s thesis, Virginia
Commonwealth University, Richmond, VA.

Galli, M., Crivellini, M., Sibella, F., Montesano, A., Bertocco, P., & Parisio, C. (2000).

Sit-to—stand movement analysis in obese subjects. International Journal of Obesity,
24, 1488-1492.

146

Gordon, C.C., Chumlea, W.C., & Roche, AF. (1988). Stature, recumbent length, and
weight. In T.G. Lohman, A.F. Roche, & R. Martorell (Eds), Anthropometric
standardization reference manual (pp. 3-8). Champaign, IL: Human Kinetics.

Goulart, F. R.-d.-P., Valls-Sole, J. (1999). Patterned electromyographic activity in the sit-
to-stand movement. Clinical neurophysiology, 110, 1634-1640.

Hesse, S., Schauer, M., Malezic, M., J ahnke, M., & Mauritz, K.-H. (1994). Quantitative
analysis of rising from a chair in healthy and hemiparetic subjects. Scandinavian
Journal of Rehabilitation Medicine, 26, 161-164.

Hughes, M.A., Myers, B.S., & Schenkman, ML. (1996). The role of strength in rising
from a chair in the functionally impaired elderly. Journal of Biomechanics, 29, 1509-
1513.

Hughes, M.A., Weiner, D.K., Schenkman, M.L., Long, R.M., & Studenski, SA. (1994).
Chair rise strategies in the elderly. Clinical Biomechanics, 9, 187-192.

Ikeda, E.R., Schenkman, M.L., Riley, P.O., Hodge, WA. (1991). Influence of age on
dynamics of rising from a chair. Physical Therapy, 71, 473-481.

Jeng, S-F., Schenkman, M., Riley, P.O., & Lin, S-J. (1990). Reliability of a clinical
kinematic assessment of the sit-to-stand movement. Physical Therapy, 70, 511-520.

Jones, F.P., Hanson, J .A., Miller, J .F., Bossom, J. (1963). Quantitative analysis of
abnormal movement: The sit-to—stand pattern. American Journal of Physical
Medicine, 8, 33-40.

Judge, J .O., Whipple, R.H., & Wolfson, L1. (1994). Effects of resistive and balance
exercises on isokinetic strength in older persons. Journal of the American Geriatrics
Society, 42, 937-946.

Kelley, D.L., Dainis A., & Wood, GK. (1976). Mechanics and muscular dynamics of
rising from a seated position. In P.V. Komi (Ed.), Biomechanics V-B (pp. 127-134).
Baltimore: University Park Press.

Kotake, T., Dohi, N., Kajiwara, T., Sumi, N., Koyama, Y., & Miura, T. (1993). An
analysis of sit-to-stand movements. Archives of Physical Medicine and
Rehabilitation, 74, 1095-1099.

Kralj, A., Jaeger, R.J., & Munih, M. (1990). Analysis of standing up and sitting down in

humans: Definitions and normative data presentation. Journal of Biomechanics, 23,
1 123- 1 13 8.

147

 

Lou, S.-Z., Chou, Y.-L., Chou, P.-H., Lin, C.-J., Chen, U.-C., & Su, F.-C. (2001). Sit-to-
stand at different periods of pregnancy. Clinical Biomechanics, 16, 194-198.

Lundin, T.M., Grabiner, M.D., & J ahni gen, D.W. (1995). On the assumption of bilateral
lower extremity joint moment symmetry during the sit-to-stand task. Journal of
Biomechanics, 28, 109-112.

Magnan, A., McFayden, B.J., & St. Vincent, G. (1996). Modification of the sit-to-stand
task with the addition of gait initiation. Gait and Posture, 4, 232-241.

Malina, R.M., & Bouchard, C. (1991). Growth, maturation, and physical activity.
Champaign, IL: Human Kinetics.

Markhede, G., & Grimby, G. (1988). Measurement of strength of hip joint muscles.
Scandinavian Journal of Rehabilitation Medicine, 12, 169-174.

Martin, A.D., Carter, J.E.L., Hendy, K.C., & Malina, RM. (1988). Segment lengths. In
T.G. Lohman, A.F. Roche, & R. Martorell (Eds.), Anthropometric standardization
reference manual (pp. 9-26). Champaign, IL: Human Kinetics.

McGraw, MB. (1943). The Neuromuscular Maturation of the Human Infant. New York:
Columbia University Press.

McMillan, AG. (1998). Development of movement coordination for a sit to stand task.
Unpublished doctoral dissertation, University of Delaware, Newark, DE.

Millington, P.J., Myklebust, B.M., & Shambes, GM. (1992). Biomechanical analysis of
the sit-to-stand motion in elderly persons. Archives of Physical Medicine and
Rehabilitation, 73, 609-617.

Mourey, F., Grishin, A., d'Athis, P., Pozzo, T., & Stapley, P. (2000). Standing up from a
chair as a dynamic equilibrium task: a comparison between young and elderly
subjects. Journal of Gerontology: Biological Sciences, 55A, B425-B431.

Munro, B.J., Steele, J.R., Bashford, G.M, Ryan, M., & Britten, N. (1998). A kinematic
and kinetic analysis of the sit-to—stand transfer using an ejector chair: implication for
elderly rheumatoid arthritic patients. Journal of Biomechanics, 31, 263-271.

Munton, J .S., Ellis, M.I., & Wright, V. (1984). Use of electromyography to study leg
muscle activity in patients with arthritis and in normal subjects during rising from a
chair. Annals of the Rheumatic Diseases, 43, 63-65.

Murray, M.P., Seireg, A.A., & Scholz, RC. (1967). Center of gravity, center of pressure,

and supportive forces during human activities. Journal of Applied Physiology, 23,
831-838.

148

 

Naumann, S., Ziv, I., & Rang, MC. (1982). Biomechanics of standing up from a chair. In
Human locomotion II: proceedings of the Second Biannual Conference of the
Canadian Society for Biomechanics (pp. 78-79). Ottawa, Ontario, Canada: University
of Ottawa.

Pai, Y.-C., Naughton, B.J., Chang, R.W., & Rogers, M.W. (1994). Control of body centre
of mass momentum during sit-to-stand among young and elderly adults. Gait &
Posture, 2, 109-116.

Pai, Y.-C., & Rogers, M.W. (1990). Control of body mass transfer as a function of speed
of ascent in sit-to-stand. Medicine and Science in Sports and Exercise, 22, 378-384.

Pai, Y.-C., & Rogers, M.W. (1991a). Segmental contributions to total body momentum in
sit-to-stand. Medicine and Science in Sports and Exercise, 23, 225-230.

Pai, Y.-C., & Rogers, M.W. (1991b). Speed variation and resultant joint torques during
sit-to-stand. Archives of Physical Medicine and Rehabilitation, 72, 881-885.

Papa, E., & Cappozzo, A. (2000). Sit-to-stand strategies investigated in able-bodied
young and elderly subjects. Journal of Biomechanics, 33, 1113-1122.

Riley, P.O., Krebs, D.E., & Popat, RA. (1997). Biomechanical analysis of failed sit-to-
stand. IEEE Transactions on Rehabilitation Engineering, 5, 353-359.

Riley, P.O., Schenkman, M.L., Mann, R.W., Hodge, W.A. (1991). Mechanics of a
constrained chair-rise. Journal of Biomechanics, 24, 77-85.

Roberton, MA. (1977). Stability of stage categorizations across trials: Implication for the
“stage theory” of overarm throw development. Journal of Human Movement Studies,
3, 49-59. ,

Roberton, M.A. (1978a). Stability of stage categorizations in motor development. In D.M.
Landers & R.W. Christina (Eds), Psychology of motor behavior and sport—I977
(pp. 494-506). Champaign, IL: Human Kinetics.

Roberton, M.A. (1978b). Stages in motor development. In M.V. Ridenour (Ed), Motor
development: Issues and applications (pp. 63-81). Princeton, NJ: Princeton Books.

Rodosky, M.W., Andriacchi, T.P., & Andersson, G.B.J. (1989). The influence of chair

height on lower limb mechanics during rising. Journal of Orthopaedic Research, 7,
266-271.

149

 

 

Roebroeck, M.E., Doorenbosch, C.A.M., Harlaar, J ., Jacobs, R., & Lankhorst, G].
(1994). Biomechanics and muscular activity during sit-to-stand transfer. Clinical
Biomechanics, 9, 235-244.

Schaltenbrand, G. (1928). The development of human motility and motor disturbances.
Archives of Neurology and Psychiatry, 20, 720-730.

Schenkman, M., Berger, R.A., Riley, P.O., Mann, R.W., & Hodge, W.A. (1990). Whole-
body movements during rising to standing from sitting. Physical Therapy, 70, 638-
651.

Schenkman, M., Riley, P.O., & Pieper, C. (1996). Sit to stand from progressively lower
seat heights—alterations in angular velocity. Clinical Biomechanics, 11, 153-158.

Schlicht, J ., Camaione, D.N., & Owen, S.V. (2001). Effect of intense strength training on
standing balance, walking speed, and sit-to-stand performance in older adults. Journal
of Gerontology: Medical Sciences, 56A, M281-M286.

Scholz, J .P., & Brandt, LC. (1997). Trajectory formation and development of the control
of standing up from sitting. Motor Control, 1, 314-339.

Schultz, A.B., Alexander, N.B., & Ashton-Miller, J .A. (1992). Biomechanical analyses of
rising from a chair. Journal of Biomechanics, 25, 1383-1391.

Seefeldt, V., & Haubenstricker, J. (1982). Patterns, phases, or stages: an analytical model
for the study of developmental movement. In J .A.S. Kelso & J .E. Clark (Eds), The
development of movement control and coordination (pp. 309-318). New York: Wiley.

Shephard, RI. (1987). Physical activity and aging (2nd ed.). Rockville, MD: Aspen
Publishers.

Shepherd, R.B., & Gentile, A.M. (1994). Sit-to-stand: Functional relationship between
upper body and lower limb segments. Human Movement Science, 13, 817-840.

Shepherd, R.B., & Koh, HP. (1996). Some biomechanical consequences of varying foot
placement in sit-to-stand in young women. Scandinavian Journal of Rehabilitation
Medicine, 28, 79-88.

Shumway-Cook, A., & Woollacott, M.H. (1995). Motor control: theory and practical
applications. Baltimore: Williams & Wilkins.

Singh, N.A., Clements, K.M., & Fiatarone, MA. (1997). A randomized controlled trial of
progressive resistance training in depressed elders. Journal of Gerontology: Medical
Sciences, 52A, M27-M35.

150

Stevens, C., Bojsen-Moller, F., & Soames, R.W. (1989). The influence of initial posture
on the sit-to-stand movement. European Journal of Applied Physiology, 58, 687-692.

Su, F.C., Lai, K.A., & Hong, W.H. (1998). Rising from a chair after total knee
arthroplasty. Clinical Biomechanics. 13, 176-181.

Vander Linden, D.W., Brunt, D., & McCulloch, M.U. (1994). Variant and invariant
characteristics of the sit-to-stand task in healthy elderly adults. Archives of Physical
Medicine and Rehabilitation, 75, 653-660.

VanSant, AF. (1988). Age differences in movement patterns used by children to rise
from a supine position to erect stance. Physical Therapy, 68, 1330-1338.

Wheeler, J., Woodward, C., Ucovich, R.L., Perry, J., & Walker, J.M. (1985). Rising from
a chair: Influence of age and chair design. Physical Therapy, 65, 22-26.

Winter, DA. (1990). Biomechanics and motor control of human movement (2nd ed.).
New York: Wiley.

Woollacott, M.H. (1986). Gait and postural control in the aging adult. In W. Bles & T.
Brandt (Eds), Disorders of posture and gait (pp. 325-336). Amsterdam: Elevier
Science Publishers B.V..

Yoshida, K., Iwakura, H., & Inoue, F. (1983). Motion analysis in the movements of
standing up from and sitting down on a chair. Scandinavian Journal of Rehabilitation
Medicine, 15, 133-140.

Yu, B., Holly-Crichlow, N., Brichta, P., Reeves, G.R., Zablotny, C.M., & Nawoczenski,

DA. (2000). The effects of the lower extremity joint motions on the total body
motion in sit-to-stand movement. Clinical Biomechanics, 15, 449-455.

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