a")?
2...!!!

.2:
LE...

(.58. ‘17
9“. ... 1:...
. it!

.723.

 

 

 

 

Q (330‘ .LIBRARY
Michigan State
University

 

 

This is to certify that the
thesis entitled

PREFERRED POSITION AND ASSOCIATED FORCES FOR
LOWER BACK SUPPORTS IN VEHICLE AND OFFICE
SEATING ENVIRONMENTS

presented by

ZAHID M RAMPURAWALA

has been accepted towards fulfillment
of the requirements for the

MS. degree in Mechanical Engineering

 

 

 

MSU is an Affirmative Action/Equal Opportunity Employer

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5/08 K'lProj/Acc8-PresICIRC/DaleDue indd

PREFERRED POSITION AND ASSOCIATED FORCES FOR LOWER BACK
SUPPORTS IN VEHICLE AND OFFICE SEATING ENVIRONMENTS

By

Zahid M Rampurawala

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Mechanical Engineering

2008

ABSTRACT

PREFERRED POSITION AND ASSOCIATED FORCES FOR LOWER BACK
SUPPORTS IN VEHICLE AND OFFICE SEATING ENVIRONMENTS

By
Zahid-M Rampurawala

The definition of seated postural comfort depends on several factors and varies
from person to person. The contour of a seat can influence the posture achieved by an
individual. This study focuses on the normal, vertical shear and lateral shear forces
exerted on 3 differently designed lower back supports by subjects from 3 anthropometric
groups in vehicle and office seating environments. Ten mid-sized males, 4 tall males and
4 short females were tested over a 2 hour period each to gather data that were statistically
analyzed by comparing the effects of each lower back support pad individually as well as
by comparing the results achieved by the 3 anthropometric groups.

Results from this research indicated that subjects exerted normal forces onto the
lower back support pads in a manner that maintained a relatively constant pressure
irrespective of pad size. Vertical shear forces exerted on the back supports depended on
the position of the pad and not on the sitter's anthropometric weight. The pad with the
longest length was positioned significantly lower than the shorter length pad. All pads
apexes were positioned below the subjects' third lumbar vertebrae locations.

Data from this research provides an insight into the preferred levels of lower back
support and position independent of a seat contour. Further, these data will be usefiil in

obtaining the appropriate ranges of support in seats with active lower back supports.

ACKNOWLEDGEMENTS

I would like to thank my research committee members: Dr. Tamara Reid Bush,
Dr. Joseph Vorro and Dr. Seungik Baek, for their vital inputs while compiling this thesis
with a special thank you to my research advisor Dr. Tamara Reid Bush for her relentless
commitment in ensuring that this research goes along the right track from the very
beginning.

I would also like to thank all my test subjects for voluntarily participating in the
research laboratory experiments. Without you all this research could not have been
completed, literally.

Eventually, I would like to thank my parents for supporting me throughout my

years at Michigan State University.

iii

TABLE OF CONTENTS

 

 

 

 

 

 

 

 

LIST OF TABLES - - -- - - -- vi
LIST OF FIGURES - - - -- - -- - -- _- -- -- _- -- -- -- - -xiii
Introduction ..... - - - .I
Literature Review -- -- -- - -- -- -- -- -- -- - 4
Overview of Research - - - - - - -12
Phase 1 - - ..... -- -- -- - -- - - - -- - - _ - ........ 13
Subjects ....................................................................................................................... 13
Methods ...................................................................................................................... 14
Data Analysis and Results .......................................................................................... 17
Phase 2 - - - - - - -- - - 23
Subjects ....................................................................................................................... 23
Equipment 26
Laboratory Experimental Seat .............................................................................. 26

Force Transducers ................................................................................................. 30
Motion Measurement System ............................................................................... 31
Methods ...................................................................................................................... 32
Data Analyses Methods .............................................................................................. 39
Body Angles ......................................................................................................... 39

Body Recline Angle .............................................................................................. 41
Thorax Angle ....................................................................................................... .42

Pelvic Angle .......................................................................................................... 43

Knee Angle ........................................................................................................... 45
Lower Back Support Pad Position ........................................................................ 46

Force Data ............................................................................................................. 47
Statistical Data Analysis - ............... - - - - -49
Data Results ........................................................................................ 50
Body Angles ................................................................................................................ 50
Body Recline Angle .............................................................................................. 50
Thorax Angle ........................................................................................................ 55
Pelvic Angle .......................................................................................................... 60

Knee Angle ........................................................................ ~ ................................... 6 5
Lower Back Support Pad Position .............................................................................. 70
Height .................................................................................................................... 70

F ore-aft Prominence .............................................................................................. 78

iv

Forces .......................................................................................................................... 83

 

 

 

 

Reference File ....................................................................................................... 83
Normal Forces ....................................................................................................... 84
Vertical Shear Forces .......................................................................................... 102

Lateral Shear Forces ........................................................................................... 108

Force Data Summary .......................................................................................... 114
Discussion - - ........ ....... -- _ ...... -- 116
Body Angles ............................................................................................................. 116
Lower Back Support Pad Position ............................................................................ 119
Height .................................................................................................................. 119

F ore-aft Prominence ............................................................................................ 121

Forces ........................................................................................................................ 122
Normal Forces ..................................................................................................... 122
Vertical Shear Forces .......................................................................................... 126
Lateral Shear Forces ........................................................................................... 126
Conclusions - - _ -- .--127
Future Work -- - - --..-132
Bibliography - - - - - -- ....... -- -- 133

LIST OF TABLES

 

 

 

Table 1: Height and weight of each subject tested in Phase 1“--- - - ..13
Table 2: Postures tested in Phase 1 - ---.15
Table 3: Definitions of measurements obtained in Phase 1--- - -.17
Table 4: Average values of defined measurements. All values are in mm .................. 19
Table 5: Classification of anthropometric groups according to height ...................... 23

Table 6: Factors differentiating the vehicle and office testing environments for

 

 

 

 

Phase 2-- - - - -- - - 24
Table 7: Subject anthropometry for Phase Z... - - - -- - - 25
Table 8: Pelvic dimensions - ..... - - - - -.-32
Table 9: Target landmarks on subject body- ...... -- - -- - - 33
Table 10: Definitions of body angles ........... - ...... 40

 

Table 11: Body Recline Angles of all 18 subjects in the office seating test
environment. All values are in degrees. Negative sign indicates rearward of vertical.
SD = Standard Deviation - <1

 

Table 12: Body Recline Angles of all 18 subjects in the vehicle seating test
environment. All values are in degrees. Negative sign indicates rearward of vertical.
SD = Standard Deviation - -- -- 82

 

Table 13: Summary of p-values of statistical tests performed for the comparison of
the effect of each pad on Body Recline Angles at each seat back recline angle. Values
in bold indicate significance (n = 18) - ......... 43

 

Table 14: Summary of p-values from statistical tests to compare BRA of each
anthropometric group individually for office seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5"I percentile females (n=4),
LM = 95th percentile males (n=4) _- 54

 

Table 15: Summary of p-values from statistical tests to compare BRA of each
anthropometric group individually for vehicle seating. Values in bold indicate

vi

significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4) - -- 54
Table 16: Thorax angles of all 18 subjects in the office seating test environment. All
values are in degrees. Negative sign indicates rearward of vertical. SD = Standard
Deviation. ....... - - - -- -- -- - S6

 

 

Table 17: Thorax angles of all 18 subjects in the vehicle seating test environment.
All values are in degrees. Negative sign indicates rearward of vertical. SD =
Standard Deviation-..-- -- -- - ......... -- -- -57

 

Table 18: Summary of p-values of statistical tests performed for the comparison of
the effect of each Pad on thorax angles at each seat back recline angle. Values in
bold indicate significance (n = 18) <8

 

Table 19: Summary of p-values from statistical tests to compare thorax angles of
each anthropometric group individually for office seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4) - - 59

 

Table 20: Summary of p-values from statistical tests to compare thorax angles of
each anthropometric group individually for vehicle seating. Values 1n bold indicate
significance. MM: 50th percentile males (n=10), SF= 5"I percentile females (n=4),
LM= 95th percentile males (n=4) - -59

 

Table 21: Pelvic angles of all 18 subjects in the office seating test environment. All
values are in degrees. Negative sign indicates posterior relative to horizontal. SD =
Standard Deviation". -------- - - - - - ----- 61

 

Table 22: Pelvic angles of all 18 subjects in the vehicle seating test environment. All
values are in degrees. Negative sign indicates inferior relative to horizontal. SD =
Standard Deviation -- -- 62

 

Table 23: Summary of p-values of statistical tests performed for the comparison of
the effect of each Pad on pelvic angles at each seat back recline angle. Values in bold
indicate significance - -- - -- - -63

 

Table 24: Summary of p-values from statistical tests to compare pelvic angles of
each anthropometric group individually for office seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95‘" percentile males (n=4) -- - - 64

 

Table 25: Summary of p-values from statistical tests to compare pelvic angles of
each anthropometric group individually for vehicle seating. Values 1n bold indicate
significance. MM= 50th percentile males (n=10), SF= 5th percentile females (n=4),
LM= 95th percentile males (n=4)---- - --------- -- - - ----64

 

vii

Table 26: Knee angles of all 18 subjects in the office seating test environment. All

 

values are in degrees. SD = Standard Deviation - 66
Table 27: Knee angles of all 18 subjects in the vehicle seating test environment. All
values are in degrees. SD = Standard Deviation 67

 

Table 28: Summary of p-values of statistical tests performed for the comparison of
the effect of each Pad on knee angles at each seat back recline angle. Values in bold
indicate significance ..... - - -- 68

 

Table 29: Summary of p-values from statistical tests to compare knee angles of each
anthropometric group individually for office seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4) - -69

 

Table 30: Summary of p-values from statistical tests to compare knee angles of each
anthropometric group individually for vehicle seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95‘“ percentile males (n=4) - - - 69

 

Table 31: Numerical data values of support pad apex height above seat pan for
office seating. All values are in mm - - - - -- - 71

 

Table 32: Numerical data values of support pad apex height above seat pan for
vehicle seating. All values are in mm- - ...... 72

 

Table 33: Support pad apex height expressed in terms of subject’s Seated Height
(SH) for office seating. SH is measured in millimeters. All other values are in
percentage. SD = Standard Deviation - - - - - -- ...74

 

Table 34: Support pad apex height expressed in terms of subject’s Seated Height
(SH) for vehicle seating. SH is measured in millimeters. All other values are in
percentage. SD = Standard Deviation - --...75

 

Table 35. Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex heights above seat pan (n=18). Values 1n bold
indicate significance -- - - 76

 

Table 36: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex heights above seat pan for each anthropometric
group considered individually (office seating). Values in bold indicate significance.
MM= 50th percentile males (n= 10), SF= 5th percentile females (n=4), LM= 95th
percentile males (n=4)-- .......... - ..... -77

 

Table 37: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex heights above seat pan for each anthropometric
group considered individually (vehicle seating). Values in bold indicate significance.

viii

MM= 50'" percentile males (n=10), SF= 5th percentile females (n=4), LM= 95tll
percentile males (n=4)-.-- - .............. -77
Table 38: F ore-aft prominences with respect to seat back of each pad for all 18
subjects in office seating. All values are in mm. Negative sign indicates the apex of
the pad was positioned rearward of the plane formed by the seat back frame ....... 79

 

Table 39: F ore-aft prominences with respect to seat back of each pad for all 18
subjects in vehicle seating. All values are in mm. Negative sign indicates the apex of
the pad was positioned rearward of the plane formed by the seat back

frame - - -- . - ----- 80

 

Table 40: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex fore-aft position relative to plane of seat back. Values
in bold indicate significance - - 81

 

Table 41: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex fore-aft prominence positions relative to the plane of
the seat back for each anthropometric group considered individually (office
seating). Values in bold indicate significance. MM = 50'“ percentile males (n=10), SF
= 5th percentile females (n=4), LM = 95th percentile males (n=4) -- -- 82

 

Table 42: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex fore-aft prominence positions relative to the plane of
the seat back for each anthropometric group considered individually (vehicle
seating). Values in bold indicate significance. MM = 50th percentile males (n=10), SF
= 5th percentile females (n=4), LM = 95th percentile males (n=4) ......................... 82

Table 43: Reference file force data values. Negative sign indicates direction of force:
inferiorly for F x, left lateral for F y and normal into the pad for F 2 8.3

 

Table 44: Normal forces (F 2) exerted on the thorax support at 10° and 15° recline
angles (office seating). All forces are in Newtons. Negative sign indicates direction of
force — into the thorax support for normal forces. SD = Standard Deviation ......... 85

Table 45: Normal forces (F2) exerted on the thorax support at 20° and 24° recline
angles (office seating). All forces are in Newtons. Negative sign indicates direction of
force — into the thorax support for normal forces. SD = Standard Deviation ......... 86

Table 46: Normal forces (F 2) exerted on each lower back support pad at 10° and 15°
recline angles (office seating). All forces are in Newtons. Negative sign indicates
direction of force - into the pad for normal forces. SD = Standard Deviation ........ 87

Table 47: Normal forces (Fl) exerted on each lower back support pad at 20° and 24°

recline angles (vehicle seating). All forces are in N ewtons. Negative sign indicates
direction of force — into the pad for normal forces. SD = Standard Deviation ........ 88

ix

Table 48: Normal forces (F2) exerted on thorax support expressed in terms of
percentage of Body Weight (BW) for office seating recline angles. Body Weight is in
Newtons. All other values are in percentage. SD = Standard Deviation- 90

 

Table 49: Normal forces (F2) exerted on thorax support expressed in terms of
percentage of Body Weight (BW) for vehicle seating recline angles. Body Weight is
in Newtons. All other values are in percentage. SD = Standard Deviation ................ 91

Table 50: Normal forces (F Z) exerted on lower back support expressed in terms of
percentage of Body Weight (BW) for office seating recline angles. Body Weight is in
Newtons. All other values are in percentage. SD = Standard Deviation ................ 92

Table 51: Normal forces (F 2) exerted on lower back support expressed in terms of
percentage of Body Weight (BW) for vehicle seating recline angles. Body Weight is
in Newtons. All other values are in percentage. SD = Standard Deviation ............ 93

Table 52: Summary of p-values of statistical tests performed for the comparison of
normal forces exerted on thorax support at all 4 recline angles. Values in bold
indicate significance (n = 18) - - 94

 

Table 53: Summary of p-values of statistical tests performed for the comparison of
normal forces exerted on each lower back support pad at all 4 recline angles. Values
in bold indicate significance (n = 18)-- - 94

 

Table 54: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on thorax support, each anthropometric being
considered individually (office seating). Values in bold indicate significance. MM =
50th percentile males (n=10), SF = 5th percentile females (n=4), LM = 95th percentile
males (n=4) - - - - - - 96

 

Table 55: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on thorax support, each anthropometric being
considered individually (vehicle seating). Values 1n bold indicate significance. MM- '-
50th percentile males (n= 10), SF= 5th percentile females (n=4), LM= 95th percentile
males (n=4)- . - - - -- - 96

 

Table 56: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on lower back support pads, each anthropometric being
considered individually (office seating). Values 1n bold indicate significance. MM— '-
50th percentile males (n=10), SF= 5th percentile females (n=4), LM= 95th percentile
males (n=4)..- - - 98

 

Table 57: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on lower back support pads, each anthropometric being
considered individually (vehicle seating). Values in bold indicate significance. MM =

50th percentile males (n=10), SF = Sth percentile females (n=4), LM = 95'" percentile
males (n=4) - - - 98

 

Table 58: Average pressure values exerted on each Pad b each anthropometric
group for office seating. 50th M = 50th percentile males, 5t F = 5th percentile females,
95th M = 95th percentile males - - 100

 

Table 59: Average pressure values exerted on each Pad by each anthropometric
group for vehicle seating. 50th M = 50"1 percentile males, 5th F = 5th percentile
females, 95th M = 95th percentile males - -- . - - - -- 101

 

Table 60: Vertical shear forces (Fx) exerted on the thorax support at 10° and 15°
recline angles (office seating). All forces are in Newtons. The negative sign indicates
an inferiorly directed force — inferiorly for Vertical Shear forces. SD = Standard
Deviation -------- -- -- - . - 103

 

Table 61: Vertical shear forces (F x) exerted on the thorax support at 20° and 24°
recline angles (vehicle seating). All forces are in N ewtons. The negative sign
indicates an inferiorly directed force - inferiorly for Vertical Shear forces. SD =
Standard Deviation - - -- - -- - 104

 

Table 62: Vertical shear forces (F x) exerted on lower back support pads at 10° and
15° recline angles (office seating). All forces are in Newtons. The negative sign
indicates an inferiorly directed force — inferiorly for Vertical Shear forces. SD =
Standard Deviation - - - - 105

 

Table 63: Vertical shear forces (F x) exerted on lower back support pads at 20° and
24° recline angles (vehicle seating). All forces are in Newtons. The negative sign
indicates an inferiorly directed force — inferiorly for Vertical Shear forces. SD =
Standard Deviation -- 106

 

Table 64: Summary of p-values of statistical tests performed for the comparison of
vertical shear forces exerted on thorax support at all 4 recline angles. Values in bold
indicate significance (n = 18). -- - - 107

 

Table 65: Summary of p-values of statistical tests performed for the comparison of
vertical shear forces exerted on each lower back support pad at all 4 recline angles.
Values in bold indicate significance (n = 18) - - 107

 

Table 66: Lateral shear forces (F y) exerted on the thorax support at 10° and 15°
recline angles (office seating). All forces are in Newtons. A negative sign indicates
that the force is directed laterally toward the left of the subject. SD = Standard
Deviation - -- - ...... 109

 

Table 67: Lateral shear forces (F y) exerted on the thorax support at 20° and 24°
recline angles (vehicle seating). All forces are in Newtons. A negative sign indicates

xi

that the force is directed laterally toward the left of the subject. SD = Standard
Deviation ...... -- - - 110

 

Table 68: Lateral shear forces (F y) exerted on lower back support pads at 10° and
15° recline angles (office seating). All forces are in Newtons. A negative sign
indicates that the force 1s directed laterally toward the left of the subject. SD- —
Standard Deviation - - - -- ----- 111

 

Table 69: Lateral shear forces (F y) exerted on lower back support pads at 20° and
24° recline angles (vehicle seating). All forces are in Newtons. A negative sign
indicates that the force is directed laterally toward the left of the subject. SD =
Standard Deviation - 112

 

Table 70: Summary of p-values of statistical tests performed for the comparison of
lateral shear forces exerted on thorax support at all 4 recline angles. Values in bold
indicate significance (n = 18) - - - 113

 

Table 71: Summary of p-values of statistical tests performed for the comparison of
lateral shear forces exerted on each lower back support pad at all 4 recline angles.
Values in bold indicate significance (n = 18)- - - 113

 

Table 72: Summary of average forces exerted on thorax support taking all subjects
into consideration. All force values are in Newtons. Negative sign indicates direction
of force: inferiorly for vertical shear, left lateral for lateral shear and into the pad
for normal forces. VS = Vertical Shear, LS = Lateral Shear ........................... 114

Table 73: Summary of average forces exerted on lower back support taking all
subjects into consideration. All force values are in Newtons. Negative sign indicates
direction of force: inferiorly for vertical shear, left lateral for lateral shear and into
the pad for normal forces. VS = Vertical Shear, LS = Lateral

Shear..-.--.- ------ -115

 

Table 74: Comparison of thorax angles at 20° and 24° seat back recline angles.
Values correspond to the 50th percentile male anthropometric group. All values are
in degrees - - ..... - -- - ...... - -- -116

 

Table 75: Comparison of knee angles at 20° and 24° seat back recline angles. Values
correspond to the 50th percentile male anthropometric group. All values are in
degrees - - - - -- -- 118

 

xii

LIST OF FIGURES

Figure 1: From left to right, posture of spine and pelvis in standing erect, seated
slumped, seated neutral and seated erect conditions ----- 4

 

Figure 2: Andersson’s experimental chair for postural studies. Figure reproduced
from Andersson4-. ------ - -- - -- - - 5

 

Figure 3: From left to right, intervertebral disc in neutral position, effects of
forward bending on disc and effects of backward bending on disc ......... 6

 

Figure 4: Difference in movement patterns of the thoracic and lumbar regions of the
spine with variation in seated postures. T — Thoracic, L — Lumbar. Figure
reproduced from Faiks and Reinecke's- -- - - - u-.....8

 

Figure 5: Test chair with independent thoracic and lumbar supports used in the
Faiks and Reinecke study. Figure reproduced from Faiks and Reineckell ................. 8

Figure 6: Supplementary backrest and lumbar pads. (a) Small pad, (b) medium pad,

 

 

and (c) large pad. Figure reproduced from Carcone and Keirl3 - -- -- 10
Figure 7: Flexible curve--.-. ----- - -- - -- -- -- -- -- -- - 14
Figure 8: Subject being tested in Phase 1 -- - --...16

 

Figure 9: [a] Initial trace of flexible curve. [b] Measurements made on trace for
design of lower back support pads - -- 18

 

Figure 10: Individual design sketches of each pad. All dimensions are in mm.
From left to right: [a] Pad 1, [b] Pad 2, [c] Pad 3. Dimensions for Pad 1 were taken
from the Standing Erect average data column while those for Pad 3 were taken from

 

 

the Seated Erect column (Table 4) -- ------- - - ----21
Figure 11: From left to right — Pads 1, 2 and 3 respectively (front view). - -22
Figure 12: From left to right — Pads 1, 2 and 3 respectively (side view) ..................... 22

Figure 13: Front view of experimental seat showing upper (thorax) and lower back
supports- - ----------- - - - -- - - 27

 

Figure 14: Seat pans used in Phase 2. Top: Office seat pan, flat along horizontal.
Bottom: Vehicle seat pan, inclined at 14° with respect to horizontal -- .-28

 

Figure 15: Sedan seat positioned behind experimental chair ...................................... 29

xiii

Figure 16: Force transducer behind the adjustable lower back support -- 30

 

Figure 17: Subject with targets attached to bony landmarks. First row, from left to
right — front view and back view. Front view targets — sternal notch, mid sternum,
RASIS and LASIS. Back view targets — C7, T7, T12, L3, MPSIS. Second row — side
view showing targets on right leg- 34

 

Figure 18: Use of pelvic support to ensure all subjects are seated upright ............... 36

Figure 19: Subject being tested in Phase 2. Top: Vehicle seating, Bottom: Office

 

 

 

 

seating-...--- ------------ -- - - - - - - - 38
Figure 20: Body Recline Angle (BRA) - - -- - - - - . -41
Figure 21: Thorax angle--- -------------------------- - - ------- - ---------------- 42
Figure 22: Determination of HJC of seated subject using the Bush-Gutowski

method3 - - - ------ -- 44
Figure 23: Knee angle ..................................................................................................... 45

Figure 24: Measurement of subject-selected position of lower back support
using L-scale.- ....... - - ----- ...46

 

Figure 25: Conversion of reference force data from reference upright position to test
recline position------ - -- -- - - - - -- - 48

 

Figure 26: Method of measurement of lower back support pad apex height above
seat pan--- -- - - -70

 

Figure 27 : Equivalence of Seated Height (SH) in erect and inclined seated
conditions. ------ - - - - - - -- - ----- 73

 

xiv

Introduction

According to a recent report', it is known that professional level office workers
spend about 70 percent of their time sitting in their offices, usually in 45 minute blocks of
time. In fact, desk-bound workers such as telephone operators, telemarketers and data
entry workers are known to spend nearly 100 percent of their work time sitting.

The simple act of sitting down involves not only an external interaction between
the sitter and the seat but also an internal mechanical interaction between certain body
elements such as the vertebrae, pelvis, intervertebral discs, muscles and skin'. Each of
these elements play an important role in a series of events associated with short and long
term sitting stresses.

The vertebrae and intervertebral discs make up what is known as the spinal
columnz. A total of 33 vertebral bodies constitute five regions of the spinal column —
cervical, thoracic, lumbar, sacral and coccygeal. The cervical region consists of seven
vertebrae generally labeled Cl through C7. Likewise, the thoracic, lumbar, sacral and
coccygeal regions have twelve, five, five, and four vertebrae each. The sacral vertebrae
are generally filsed to form the sacrum while the coccygeal vertebrae are generally fused
to form the coccyx bone.

Intervertebral discs, found between vertebrae3, are flat, round structures about a
quarter to three quarters of an inch thick with tough outer rings of tissue called the
annulus fibrosis that contain a soft, white, jelly-like center called the nucleus pulposus3.

Flat, circular plates of cartilage connect to the vertebrae above and below each disc.

These intervertebral discs act as shock absorbers for the spine. They compress when
weight is put on them and spring back when the weight is removed.

Intervertebral discs make up about one-third of the length of the spine and
constitute the largest organ in the body without its own blood supply. The discs receive
their blood supply through movement as they soak up nutrients. Since the discs are
avascular, the supply of nutrients depends on the diffusion of substances from
surrounding areas, rather than directly from the supply of blood3.

In a normal standing posture, the spinal column has a curvature which can be seen
in the lateral plane. The thoracic region is curved outward (posteriorly) of the body
termed as a kyphotic curvature. The lumbar region on the other hand is curved inward
into the body (anteriorly) and this is termed as a lordotic curvature.

Pelvic rotation plays an important role in determining the spinal curvature4. When
a person sits, the pelvis tends to rotate rearward. This results in a loss of lumbar lordosis
leading to straightening of the lower back. Pressure is applied on the anterior portions of
the intervertebral discs while the posterior portions are spread apart. This loss in lumbar
lordosis pulls the spine a few centimeters away from the upper body’s center of gravity.
In this position, the torso tends to hang in the anterior direction resulting in a slumped
posture. To prevent this, the muscles attached to the lower back contract strongly and
steadily.

Spinal ligaments, such as the anterior and posterior longitudinal ligaments, allow
efficient passive joint stabilization. They also limit and direct vertebral movement.

Correct aid for suitable seating is essential to prevent ligament damage.

Based on the composition of the spine and the postures assumed, seated postures
have been shown to lead to various back problemss. According to statistical studies
conducted on the United States population, “back problems are the most frequent cause
of activity limitations in working-age adults". Twenty-two percent of all workers’
compensation claims and 31 percent of all workers’ compensation dollars are for lower
back pain7. Among chronic disorders, lower back pain is the second greatest cause of
visits to physiciansg.”

Many researchers believe that sudden back problems are in fact a result of long
term damageg. Ensuring a proper seated posture with appropriate support during our
everyday lives is important in reducing back problems. While seated, the presence of a
lumbar or pelvic support helps the lower back muscles to relax'. This in turn helps
maintain lordosis and reduce the forward slouching or slumping of the torso. Rearward
inclination of the backrest further provides relief to the intervertebral discs since the load
is now supported by the seat back rather than by the spine. However, proper stabilization
and support of the lower back is only possible if the lower back support is appropriately
designed and allows freedom of active motion for postural changes. Across the large
number of anthropometric groups, it is difficult to narrow down to a single design of
lower back support.

Hence the current research focuses on the variation in two design parameters for
lower back supports: length and prominence. The effects of these two parameters on
support position, body posture and support forces of subjects from three anthropometric
groups were studied. Results from this study may motivate vehicle seat and office chair

designers to reconsider what the occupant desires in terms of lower back support.

Literature Review

According to a previous study by Akerblom'o, a firm backrest support should be
located in the lower region of the seat back to prevent excessive flexing of the lumbar
spine. Akerblom suggested that the support pad be placed at the top of the pelvis starting
at the location of the fourth or fifth lumbar vertebra. Keeganl "'2 found that people with
low—back disorders preferred sitting reclined with lumbar lordosis as compared to sitting
upright with relatively flat lumbar curvatures. This led Keegan to suggest a seat design
that would result in a lumbar lordosis midway between a typical standing lordosis and a
flat spinal curvature. In order to allow free rotation of the pelvis to accommodate
different postures (Figure 1), both Akerblom and Keegan recommended a gap of
approximately 1 15 mm between the lumbar support and the seat pan. It is however
unclear if this 115 mm recommendation is below the lower edge of lumbar support or
below the lower edge of seatback.

Figure 1: From left to right, posture of spine and pelvis in standing erect,
seated slumped, seated neutral and seated erect conditions.

(I if”

. - 1 ,14,15.16,I7
Andersson and h1s research team conducted experiments 3

yielding
results that differed from the recommendations by Akerblom and Keegan. Andersson
used radiographic techniques to study the influence of backrest inclination and lumbar
support on the shape of the lumbar spine in various sitting postures. Four angles of
backrest inclination along with four positions of lumbar support prominence were
included in addition to each lumbar support being positioned at three different lumbar
levels in terms of height (Figure 2). Andersson suggested that lumbar supports should be
designed to maintain a standing lordosis while seated and should be located at
approximately the height of the third lumbar vertebra with the intention of reducing

lumbar spine loads and intradiscal pressure caused by body weight and spinal curvature

(Figure 3).

Figure 2: Andersson’s experimental chair for postural studies. Figure reproduced

from Andersson”.

 

 

 

 

 

 

 

 

 

80° 1000
T 110° T
+4cm A ~20m
a? It"
1’ f“
I K. I T.
_ J _ L

 

 

 

 

 

 

 

 

Figure 3: From left to right, intervertebral disc in neutral position, effects of
forward bending on disc and effects of backward bending on disc.

I I
a$
, t. . "a
I 2
- L
i J:
“7713.17.13 ' ’ ' ‘ - - w...-
...‘L‘ ’ ‘ “ ~‘-.° ..H.
. \
1t“ . 9v!)
‘ka‘upm . ' 'i‘h‘
"T‘é ab.'-a'.vuz:qcrfiiu 21.3; envy-v“-

   

Porter and Norrisl8 compared Andersson’s results with subject preferences. Male
and female subjects were included in their experiments and were asked to sit in an
experimental chair while subjected to variations in seat back and seat pan angles
matching those used by Andersson. Subjects were allowed to adjust the vertical height of
the lumbar support to any position, however horizontal prominence was restricted to
fixed distances of 0, 20 or 40 mm. Porter and Norris concluded that subjects preferred the
20 mm prominence even though it did not yield the maximum lumbar lordosis. Hence,
according to Porter and Norris postures suggested by Andersson using 40 and 50 mm
prominences were not generally preferred by sitters. Porter and Norris also found that the
preferred lumbar support height was approximately 120 mm above the hip joint center,
albeit with variation among subjects.

Reed’s studyl9 partly agrees with the one conducted by Porter and Norris by
recommending seated lumbar lordosis to be less than the standing lordosis. Reasons

stated were the inappropriate distributions of support force and discomfort. However,

Reed’s study differed in terms of numerical data suggesting a vertical position of the
lumbar support apex at about 152 mm above the sitter’s hip joint centers. Horizontal
prominence was found to lie between 0 and 25 mm according to subject preferences with
an average prominence of 1 1 mm. Reed’s work was carried out in the vehicle seating
configuration only.

Faiks and Reinecke20 defined the function of the backrest to “stabilize the torso’s
posture, support spinal curvature and reduce vertical loading of the upper trunk to the
backrest thereby reducing the loading on the spine.” They found that backrest inclination
helped reduce spinal loading by as much as 31%. Also, a change from an upright to a
reclined position results in an increase in both lumbar lordosis and thoracic kyphosis.
However, the path and rate of motion of the lumbar spine (L3) was found to be
independent of the path and rate of motion of the thoracic spine (T6) as shown in Figure
4. Both parameters were found to be related to pelvic rotation and changes in spinal
curvatures. Results from this study indicated that the magnitude of support at the lumbar
and thoracic regions were similar in an upright posture, values being 69.1 N average
lumbar force and 61.1 N average thoracic force. However, in a reclined posture, the rate
of force change for the thoracic region was much sharper than that for the lumbar region,
yielding 80.6 N average lumbar force and 108.7 N average thoracic force. This gave an
increase of 2.5 N of force at thoracic region for every degree of back inclination as
compared to a much smaller value of 0.6 N at the lumbar region. F aiks concluded that
these differences in force levels must be taken into consideration to ensure that the

backrest plays the dual role of supporting posture and allowing simultaneous natural

motion of the spine. This would require the backrest to include upper and lower support
mechanisms that could be independently adjusted (Figure 5).
Figure 4: Difference in movement patterns of the thoracic and lumbar regions of the

spine with variation in seated postures. T — Thoracic, L —- Lumbar. Figure
reproduced from Faiks and Reinecke”.

 

Figure 5: Test chair with independent thoracic and lumbar supports used in the
F aiks and Reinecke study. Figure reproduced from Faiks and Reinecke”.

 

 

Goossens and Snijders2| studied the influence of scapular support on the effects of
lumbar support. In this study, forces on shoulder and seat were measured separately while
those on the pelvis were calculated using static equilibrium equations. Seat back recline
angles were varied through a range of 0° to 17°. Free shoulder space was defined as “the
distance between the tangent to the lumbar support and the parallel tangent to the
scapular support.” Results from this study suggested that leaving no free shoulder space
resulted in highest back muscle activity while a free shoulder space of at least 6 cm not
only reduced back muscle activity significantly but also allowed for proper lumbar
support. A high and straight backrest was hence an inappropriate design as per the
recommendations from this study. These factors were taken into consideration while
designing the laboratory experimental seat for the current study.

Carcone and Keir22 conducted a study to examine the effects of backrest
configuration on seat pan and backrest pressure, spinal posture and comfort. The study
included subjects being tested in five backrest configurations: chair only, chair with
supplementary backrest and with each of three lumbar pads varying in thickness (Figure
6). The supplementary backrest used was a polyurethane frame with an outer foam layer
supplied with a removable lumbar pad attached by Velcro. Lumbar lordosis was greatest
with the large pad, but not the most preferred posture by the subjects. However, the
lumbar supports were positioned at the L3 level for all subjects without any allowable

movement of pads as per subject preference.

Figure 6: Supplementary backrest and lumbar pads. (a) Small pad, (b) medium pad,
and (c) large pad. Figure reproduced from Carcone and Keir”.

 

In a recent study by Bush and Hubbard”, distribution of normal and shear forces
exerted by the sitter on the seat and the variation in these forces with changes in seating
position were determined. Three inclination angles and four different levels of seat back
articulation were included in the experiments. Force transducers were placed behind the
thorax, pelvis and steering wheel and under the foot, thighs and buttocks. Twenty three
midsized male subjects were tested in these conditions. Results from this study drew
conclusions that with change in seat back inclination or change in torso articulation,
significant shifts in force distribution occur. Normal forces of 24.8 N and 31.3 N were
measured in the pelvic region at recline angles of 20° and 24° respectively with
corresponding normal force values of 184.3 N and 204.1 N in the thoracic region.
Though the pelvic support allowed articulation, it did not allow movement and
positioning as per subject preference.

In the current study, several parameters were taken into consideration which

makes it unique to those presented earlier. Subject controlled movements of lumbar

supports in both the vertical and horizontal directions were allowed. Three differently
contoured firm supports made of wood were used. The upper back support was
positioned at the T7 level for all subjects, allowing sufficient free space between the
upper and lower back supports. Four seat back recline angles, two seat pan recline angles
and three lower back support pads formed a matrix of trials to which 18 subjects
belonging to three different anthropometric groups were subjected. Vertical position and
horizontal prominence of lower back support pads along with forces exerted on both

lower and upper support pads were determined.

11

Overview of Research

The focus of this research was to test two independent design parameters of
length and prominence of lower back supports and how these affect dependent
parameters of body posture, support position, and support force levels of subjects from
three different anthropometric groups.

For this research, laboratory experiments were conducted in two phases:

The purpose of Phase 1 was to obtain the spinal curvature shapes of subjects from
a range of anthropometric groups. Subjects were tested in four postures: standing erect,
standing relaxed, seated erect and seated relaxed. These curvatures were then further
analyzed to obtain dimensions for the construction of three differently contoured lower
back support pads to be used in Phase 2.

The purpose of Phase 2 was to test 18 subjects from three different
anthropometric groups in office and vehicle seating environments to collect data
regarding subject-preferred positioning of lower back support and the forces exerted on
these supports at different seat back recline angles.

Over the course of the following sections, Phase 1 will first be discussed in its

entirety followed by Phase 2.

12

Subjects

For this phase, 1 1 subjects (six males and five females) were tested. They ranged
in height from 59 inches to 77 inches and weight from 92 pounds to 288 pounds. Table 1
lists the gender, height, weight and standing height details of all subjects. The purpose of
this testing phase was to obtain the spinal curvature shapes of subjects from a range of
anthropometrics to guide the development of three differently contoured lower back

support pads. Phase 1 testing for each subject lasted for approximately 30 minutes.

Phase 1

Table 1: Height and weight of each subject tested in Phase 1.

 

 

Subject Gender Height Weight Seated Height

ID
inches (cms) lbs (Newtons) inches (cms)

P02 M 68.5 (174.0) 171 (759) 35.0 (88.9)
P03 M 77.0 (195.6) 288 (1279) 39.0 (99.1)
P04 M 68.0 (172.7) 143 (635) 35.5 (90.2)
P05 M 68.5 (174.0) 168 (746) 35.0 (88.9)
P06 F 60.3 (153.0) 113 (502) 31.0 (78.7)
P07 F 64.5 (163.8) 122 (542) 35.0 (88.9)
P08 M 77.0 (195.6) 263 (1168) 39.0 (99.1)
P09 M 68.5 (174.0) 129 (573) 35.0 (88.9)
P10 F 59.0 (149.9) 92 (408) 30.5 (77.5)
P11 F 64.3 (163.2) 124 (551) 35.0 (88.9)
P12 F 68.5 (174.0) 165 (733) 37.0 (94.0)

Average 67.7 (171.8) 162 (718) 35.2 (89.4)
SD 5.7 (14.6) 62 (274) 2.7 (6.8)

 

13

 

Methods

All subjects testing was approved by the University Committee on Research
Involving Human Subject (UCRIHS). Before testing, the protocol was reviewed with the
subject and he/she was asked to voluntarily sign a consent form, IRB # 07—698, to grant
permission to be tested, interviewed and photographed. Once informed, each subject was
asked to wear a tight-fitting top such as an athletic top so that the spinal curvature
obtained would not be affected by movement of loose clothing. Also, tight clothing
helped in easy palpation of spinal vertebrae. Physical dimensions such as height, weight
and seated height were taken. A flexible curve (Figure 7) covered with white tape was

used to obtain the spinal curvatures.

Figure 7: Flexible curve

 

The twelfth thoracic (T12), five lumbar (L1, L2, L3, L4, L5) and the first sacral
(S l) vertebrae were palpated and their positions marked onto a tape attached to the
subject’s clothing. The flexible curve was then gently pressed along the subject’s back
(Figure 8) starting from the seventh cervical vertebra (C7) all the way down to the sacral
region. The palpated positions were then correspondingly marked onto the curve. This
protocol was followed for each posture described in Table 2. For the seated postures,
each subject was asked to be seated on a stool with an approximate 90° knee angle. The
flexible curve was then removed from the subject and traced on a large sheet of paper and

the various vertebral locations identified on the paper.

Table 2: Postures tested in Phase 1.

 

 

Posture Description
Standing Erect Maximum erect position
Standing Relaxed Comfortable but not slumped
Seated Erect Maximum erect position
Seated Relaxed Comfortable but not slumped

 

15

 

Figure 8: Subject being tested in Phase 1.

 

Data Analysis and Results

After the curve was traced on paper, vertebral landmark locations were identified

and pertinent measurements, described in Table 3 and shown in Figure 9, were made on

the trace. These data were used in the design and construction of three differently

contoured lower back support pads.

Table 3: Definitions of measurements obtained in Phase 1. Please refer to

Figure 9 for a diagrammatic sketch of these measurements.

 

Measurement
T12-SI

X-Y

Z-Y

A-B

Z-B

T12-Z

LZ-Q

Sl-Y

 

Description
Actual curvature length from T12 to S1.

Vertical length from point of maximum kyphosis (X) to
horizontal line passing through S 1.

Vertical length from T12 to 81 along line tangent to point of
maximum kyphosis.

Horizontal line indicating maximum lumbar lordosis regardless
of location.

Vertical length from Z to horizontal line A-B (distance between
T12 and horizontal plane of maximum lordosis).

Horizontal length from T12 to vertical line X-Y indiacting
lordosis / kyphosis at T12.

Horizontal length from L1 to vertical line X-Y indicating
lordosis / kyphosis at Ll.

Horizontal length from L2 to vertical line X-Y indicating
lordosis / kyphosis at L2.

Horizontal length from $1 to vertical line X-Y indicating
lordosis at 81.

 

17

 

Figure 9: [a] Initial trace of flexible curve.
[b] Measurements made on trace for design of lower back support pads.

 

 

la] [b]

C?\

l
l

T12 T12
L1 L1
1.2 1.2
1.3 A
1.4

‘\ .

 

 

 

 

 

 

I
-

 

./

 

 

’

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

,o *0

 

 

 

 

 

 

 

 

 

 

 

 

 

L5
SI

 

 

 

 

 

 

 

 

 

Sl

 

 

 

”“1

j

18

Curvature length T12—S1 was measured using a flexible measuring device. The
device was traced along the curvature starting from T12 down to SI and then straightened
to be measured with a scale. All other dimensions were measured using a regular scale.
Average values of the previously defined measurements for each of the four tested

postures were then calculated. Results are given in Table 4.

Table 4: Average values of defined measurements. All values are in mm.

 

Measurement Standing Standing Seated Seated
Erect Flexed Erect Flexed
T12-S] 188 197 221 227
Z-Y 182 184 207 223
A-B 44 40 27 39
Z-B l 12 122 152 213
T12-Z 22 17 9 3
Ll-P 29 24 14 8
L2-Q 35 3 1 18 13
Sl-Y 25 28 ’1 6 38

 

 

 

Next, three lower back support pads were designed around the average spinal
curvature data collected in Phase 1. Consideration of prominence and contact length were
deemed important factors. Pads 1 and 3 were constructed with similar lengths, while Pads
2 and 3 had similar levels of maximum prominence (Figure 10). To allow each pad to
have its own significant effect on seated postures, Pads 1 and 2 were made with the
maximum and minimum prominences obtained from Table 4 (dimension A-B, maximum
= 44.0 mm, minimum = 27 mm). On the other hand, since Pads 2 and 3 had similar
prominences, Pad 2 was made much smaller in length as compared to Pad 3.

In addition to the maximum and minimum prominences, dimensions from the

Standing Erect and Seated Erect columns of data (Table 4) were used to construct Pads 1

l9

and 3 respectively. Figure 10 ([a], [b] and [c]) demonstrates the design of Pads 1, 2 and 3
respectively. For Pads 1 and 3, the design sketch started with a vertical line of length Z-
Y. For Standing Erect posture, Z-Y = 182 mm while that for Seated Erect was 207 mm.
The larger of the two was chosen. Line A-B was then drawn perpendicular to Z-Y at a
distance Z-B from Z. The dimension Z-B was also taken from Table 4 where Z-B = 112
mm for Pad 1 (Standing Erect column) and Z-B = 152 mm for Pad 3 (Seated Erect
column). The length of line A-B equaled the desired prominence, that is, 44 mm for Pad
1 and 27 mm for Pad 3. Using a roller scale, lines T12-Z, Ll-P, L2-Q and Sl-Y were
drawn parallel to line A-B with points Z, P, Q and Y all lying on the vertical line Z-Y.
The dimensions of these lines were taken from their corresponding values in Table 4
under the Standing Erect and Seated Erect columns and have been shown individually for
each pad in Figure 10. Following this, a smooth curve was drawn through points T12, L1,
L2, A and S1. Finally, the upper and lower ends of the sketch were rounded off to form a
smooth connection between the curve and the vertical line Z-Y.

As mentioned previously, Pad 2 was constructed with a prominence similar to Pad
3 but much shorter in length. The length of Pad 2 was determined by taking
approximately 75 mm on either side of the apex line of Pad 3, staying within the lumbar

region.

20

Figure 10: Individual design sketches of each pad. All dimensions are in mm.
From left to right: [a] Pad 1, [b] Pad 2, [c] Pad 3. Dimensions for Pad 1 were
taken from the Standing Erect average data column while those for Pad 3 were
taken from the Seated Erect column (Table 4).

[c] Pad 3

 

 

 

 

 

 

 

 

 

21

Figures 11 and 12 are actual photographs of the three pads. All pads were made
from wood. The black lines on each of the three pads indicate the apex position.

Hence, for Phase 2 testing, it was now possible to compare subject preferences
between two pads of similar lengths (Pad 1 and Pad 3) and two pads of similar

prominence levels (Pad 2 and Pad 3).

Figure 11: From left to right — Pads 1, 2 and 3 respectively (front view)

 

 

Support
pad
attachment
to seat
back

 

 

 

 

22

Subjects

Phase 2

For Phase 2, a total of 18 subjects from three anthropometric groups - 50‘h

percentile males (n=10), 5’h percentile females (n=4) and 95th percentile males (n=4),

were tested. Classification of these anthropometric groups was based on height as defined

by the 1988 Anthropometric Survey of US Army Personnel Interim Report24. A deviation

of up to 1.5 inches on either side of the defined height was allowed while selecting

subjects for Phase 2. Table 5 gives the target height ranges of the three anthropometric

groups. These groups are standards for the automotive and office industries. Each of

these 18 subjects was tested in both vehicle and office environments.

Table 5: Classification of anthropometric groups according to height.

 

Anthropometric
Group

5‘" percentile females
50th percentile males
95th percentile males

 

Defined
Height24
inches (cm)

60.1 (152.8)
69.1 (175.5)
73.5 (186.7)

Allowed Height
Range
inches

58.5 - 61.5
67.5 - 70.5
72.0 - 75.0

 

 

23

The difference in the two environments lay in three areas: recline of seat back,

inclination of seat pan and inclination of footrest. These factors are described in Table 6.

Table 6: Factors differentiating the vehicle and office testing environments for

 

 

Phase 2.
Factor Office Vehicle
Recline Angle 10°, 15° (wrt* vertical plane) 20°, 24° (wrt* vertical plane)
Seat pan Flat wrt* horizontal plane Inclined at 140 wrt*
horizontal plane
Footrest inclination Subjects feet flat on footrest Subjects feet rested on a 61°
inclined support

 

 

*wrt = with respect to.

Each of the three back support pads designed as per the data gathered in Phase 1
testing, were tested with each subject at each of the four recline angles given above,
repeated twice for each posture making a total of 24 trials for each subject. The order of
the pads being tested was randomized and so was the order of the testing environment.
This ensured that the data collected was not affected by a fixed pattern of testing. Phase 2
testing for each subject lasted between 2 to 2.5 hours. The anthropometric data of all 18
subjects is given in Table 7. The average height of each anthropometric group almost
equals the defined height as per the 1988 Anthropometric Survey of US Army Personnel

Interim Report”.

24

Table 7: Subject anthropometry for Phase 2.

 

Subject ID Age Height
(years) inches (cms)

Weight
lbs (Newtons)

Seated Height
inches (ems)

5th percentile females

 

P2K 23 60.0 (152.4) 88 (391) 32.0 (81.3)
P2L 23 59.3 (150.5) 110 (488) 31.0 (78.7)
P2M 23 59.0 (149.9) 103 (457) 30.0 (76.2)
PZN 28 61.5 (156.2) 137 (608) 31.0 (78.7)
Average 24.3 60.0 (152.3) 110 (486) 31.0 (78.7)
so 2.5 1.1 (2.8) 21 (91) 0.8 (2.1)
50"I percentile males
P2A 23 68.5 (174.0) 178 (790) 34.0 (86.4)
P213 23 70.0 (177.8) 166 (735) 37.5 (95.3)
P2C 23 68.0 (172.7) 135 (597) 35.3 (89.5)
P21) 24 68.0 (172.7) 163 (724) 34.5 (87.6)
PZE 24 69.0 (175.3) 125 (555) 35.0 (88.9)
P2F 22 70.0 (177.8) 160 (708) 35.5 (90.2)
P2G 27 68.0 (172.7) 137 (608) 36.0 (91.4)
P2H 26 69.8 (177.2) 164 (730) 36.0 (91.4)
P21 26 68.0 (172.7) 169 (750) 35.0 (88.9)
P21 26 68.3 (173.4) 148 (657) 35.5 (90.2)
Average 24.4 68.8 (174.6) 154 (686) 35.4 (90.0)
so 1.7 0.9 (2.2) 17 (77) 1.0 (2.4)
95th percentile males
PZU 24 72.5 (184.2) 253 (1123) 40.0 (101.6)
NV 23 72.0 (182.9) 300 (1332) 38.5 (97.8)
PZW 21 72.8 (184.8) 162 (719) 39.5 (100.3)
P2X 25 74.8 (189.9) 182 (808) 39.3 (99.7)
Average 23.3 73.0 (185.4) 224 (996) 39.3 (99.9)
so 1.7 1.2 (3.1) 64 (283) 0.6 (1.6)

 

25

 

Equipment

Laboratory Experimental Seat

For this study, an experimental seat was designed and built to allow the lower
back support pads to move in vertical as well as fore-aft directions. These movements
were made possible by making use of two small screw motors attached to a solid steel
frame. One motor allowed vertical movement while the other enabled fore-aft motion of
the pads. Both motors were operated by an electrical switch which activated movements
in all four directions. The switch was controlled by the test subject. Power for the switch
was obtained from a 12 V battery.

The experimental seat was built using unistrut pieces for the chair and seat back
frame. There were only two supports along the seat back in contact with the subject, one
located at the thorax and the other being the lower back support pad. Rectangular wooden
pieces were used for the seat pan, thorax and lower back supports. Unlike the lower back
support pads, the seat pan and the thorax support were covered with a thin layer of foam-
backed fabric. The unistrut pieces had holes in them at regular intervals of 1 inch. These
holes allowed the height adjustment of the thorax support such that it was positioned near

the seventh thoracic vertebra for each test subject (Figure 13).

26

Figure 13: Front view of experimental seat showing upper (thorax) and lower back
supports.

  

 

Thoracic
suppon ‘

 

Lower
back
support

 

 

 

Due to the desire to mimic two different environments, the office and automotive,
certain features were adjusted or changed based on the environment. There were two seat
pans constructed, one for the office setting and the other to represent a vehicle seat. The
office seat pan was flat, lying along a horizontal line, while the vehicle pan was inclined
at angle of 14° with respect to the horizontal plane (Figure 14). This angle of 14° is a
common seat pan angle for vehicle seat testing. Both seat pans and the thoracic back
support were covered with a foam-backed fabric of approximately 15 mm in thickness

(13 mm of foam and 2 mm of fabric).

27

Figure 14: Seat pans used in Phase 2.
Top: Office seat pan, fiat along horizontal.
Bottom: Vehicle seat pan, inclined at 14° with respect to horizontal.

 

  
 

28

The entire steel structure for the seatback was placed in a sedan seat positioned

behind the experimental chair (Figure 15). This served two purposes. It provided a base

support for the steel structure which was a heavy piece of equipment. Also, the sedan seat

already had a built-in reclining mechanism. This mechanism was used to recline the

experimental chair by bolting the two together with wooden pieces. Also, the reclining

motion of the sedan seat could be locked at any desired recline angle.

Figure 15: Sedan seat positioned behind experimental chair.

 

Thorax support force

W transducer

 

 

 

   
   

Lower back support
force transducer

switch

29

Thorax
support

 

 

 

Lower
back
support

 

 

F orce Transducers

Two multi-channel force transducers (also called load cells) were used along with
the experimental chair. One was located behind the thoracic support and was kept fixed
while the other was located behind the lower back support pad (Figure 16) and moved
with the pad. These force transducers measured support forces in three directions Fx, Fy,
FZ and three moments Mx, My, Mz relative to the center of the force transducer. The two
force transducers together recorded the forces exerted by the subject in the upper as well
as lower back regions.

Each of the two force transducers had a capacity of 250 1b (1112 N). The force
plates were Advanced Mechanical Technology Inc. (AMTI) MC3A series plates. These
plates measured 3 inches in height, width and depth. The force transducers were used in
conjunction with AMTI amplifiers. The amplifiers were set to a gain of 1000 and a filter
of 10.5 Hz. Each force transducer came with factory measured sensitivities for each
channel. These sensitivities were incorporated into the calibration file (LabView 7.1) for

data processing.

Figure 16: Force transducer behind the adjustable lower back support.

 

30

Motion Measurement System

A Qualisys MacReflexTM motion measurement system”, consisting of a set of
five cameras, was used to record the three dimensional positions of retro-reflective
targets placed on the seat pan a swell as anatomical reference points of each subject. Data
were collected at 12 Hz over a period of 5 seconds. This system was calibrated every
time before testing a subject”. Infra-red light rings around the lens of each camera
enabled the camera to capture the three dimensional data of the targets in the laboratory
ambient light.

Targets were made oflightweight spherical balls and covered with 3M high gain,
7610 retro-reflective tape. This tape and the shape of the targets enhanced their visibility.
A flexible material was used as the base attachment for each target. This material was

taped onto the anatomical landmarks of each subject.

31

Methods

As with Phase 1, testing began with a detailed explanation of the procedures.
Consent forms were required to be signed by every participant granting the investigator
permission to test, interview and photograph him/her. Before starting off, questions
pertaining to the subject’s general lifestyle and which would be relevant to this research
study were asked. If the subjects noted they had experienced any back or neck pain that
day, they were excluded from testing. Female subjects who were pregnant were also
excluded from testing.

Once the lifestyle questionnaire was completed, physical dimensions such as
height, weight and seated height were taken. In addition, three pelvic dimensions

described in Table 8 were also measured with an anthropometer.

Table 8: Pelvic dimensions

 

Dimension Definition

Pelvic Width Measurement from ASIS to ASIS

Pelvic Height Vertical measurement from pubic symphysis to inter-ASIS line
Pelvic Depth Measurement from A818 to PSIS

 

 

 

The seventh thoracic vertebra (T7) was palpated and marked with tape. The
subject was asked to sit erect on a stool and the height of T7 above the stool pan surface
was measured. This was done to position the thoracic support at approximately the
subject’s T7 location on the experimental chair in the most upright position.

Following the anthropometric measurements, each subject was targeted with
light-weight, retro-reflective markers on the body bone landmarks listed in Table 9 and

shown in Figure 17.

32

Table 9: Target landmarks on subject body

 

 

C7:
T7:
T12:
L3:

MPSIS:
RASIS:
LASIS:

MS:
SN:
RT:
RK:
RLL:

Body Landmarks

Seventh cervical vertebra

Seventh thoracic vertebra

Twelfth thoracic vertebra

Third lumbar vertebra

Mid Posterior Superior Iliac Spine
Right Anterior Superior Iliac Spine
Left Anterior Superior Iliac Spine
Mid Stemum

Stemal Notch

Right Thigh

Right Knee

Right Lower Leg

 

33

 

Figure 17: Subject with targets attached to bony landmarks.
First row, from left to right — front view and back view.
Front view targets — sternal notch, mid sternum, RASIS and LASIS.
Back view targets —- C7, T7, T12, L3, MPSIS.
Second row — side view showing targets on right leg.

 

 

 

    
  

Right thigh
Right knee

Right
lower leg

 

 

 

 

34

Each of the anatomical landmarks was palpated, and those that were not covered
with any clothing were cleaned with an alcohol swab and a gauze pad to ensure that the
medical tape used to attach the targets would adhere to the skin. To identify seat pan
height, one target was also attached to the side surface of the experimental chair’s seat
pan.

With the subject targeted, a reference file was taken with the subject seated erect
in the experimental chair but not touching the seat back. This served as a baseline
measure and marked the heights of C7, T12, L3 and mid-PSIS relative to the seat pan.
This static reference file was captured over a period of 5 seconds using the Qualisys
MacReflexTM motion system software”. With this completed, targets on T7, T12, L3 and
mid-PSIS were removed.

Next the subject was asked to sit all the way back into the experimental chair with
his/her buttocks first touching a foam-covered, removable rectangular board (Figure 18)
and then his/her back leaned against the thoracic support. The use of this board was to
ensure that each of the subjects was seated with his/her buttocks in the same plane as the

thoracic support. The board was then gently removed.

35

Figure 18: Use of pelvic support to ensure all subjects are seated upright.

 

Pelvic support (removed
after subject was seated)

 

 

At this stage, the lumbar support was not in contact with the subject’s back and
was at approximately midway between the thoracic support and the seat pan. Depending
on whether the subject was being tested in the vehicle or office environment, he/she was
provided with the appropriate footrest. For the office setting, the subject was allowed to
adjust the height as well as fore-aft position of the footrest as per their comfort
requirements. However, for the vehicle setting, only fore-aft movement of footrest was
allowed with no height adjustment permitted. This is because with most vehicle seats
only a fore-aft movement is possible while almost every office seat allows for height
adjustment as well. With the subject seated this 'way, the investigator gave a brief
demonstration of the possible movements of the lumbar support pad by using the electric
switch. The subject was then asked to use the switch himself/herself and position the pad

where they felt comfortable. The lumbar pads were not covered with any fabric or foam.

36

This was to ensure that the true shape of each pad was reflected in the final posture
chosen by the subject.

Each subject usually took approximately a minute to adjust the pad to their
desired position. They were allowed to make as many pad movements as needed and in
any order, that is, there was no restriction on first having a vertical and then fore-aft
motion or vice-versa. With the pad positioned, the subject was asked to keep his/her
hands by his/her side and remain still for two minutes. For the first minute, no action was
performed by the investigator to allow the subject to settle into the chair. During the
second minute, the subject’s position was captured by the motion measurement system
software simultaneously with force readings being recorded using LabView software.
The subject was then asked to get up from the experimental seat and the investigator then
measured the vertical and fore-aft position of the support pad using an L-shaped scale.
One arm of this scale gave the fore-aft measurement while the other gave the vertical
reading by coinciding with another scale planted vertically along the seat back. A spirit-
level was attached to the L-shaped scale to ensure that the reading was taken with the
scale perfectly horizontal. This completed one trial. Each trial lasted for approximately
four to five minutes.

As mentioned previously, each of the three support pads was tested twice at each
of the four recline angles of 10°, 15°, 20° and 24". These recline angles were measured
with an inclinometer and the order of the pads was randomized. Phase 2 testing for each
subject lasted for approximately two hours (Figure 19). During the entire testing period,
the subject’s attention was diverted from the test procedures by having a movie playing

on a laptop placed a few feet in front of him/her. Care was taken to keep the laptop at the

37

subject’s eye-level to prevent any sort of neck stiffness by the end of the testing

procedure.

Figure 19: Subject being tested in Phase 2.
Top: Vehicle seating, Bottom: Office seating.

 

 

 

38

Data Analyses Methods

Data obtained from Phase 2 has been broadly classified into three major
categories for analysis — body angles, lower back support pad positions and force data
analysis. Accordingly, the analysis methods for each of these three categories are

described in this section.

Body Angles

To calculate angles of different body parts in different seated postures, co-
ordinate data of the retro-reflective targets attached to the subject's body were required to
be captured. This system was calibrated every time before testing a subject following the
instructions given in the system's user manual”. The motion system software was used
to gather, track, label, and export the three dimensional coordinates of all targets.

Four body angles were calculated for each subject using the data capture by the
motion measurement system. These are the thorax angle, the pelvic angle, the Body
Recline Angle (BRA) and the knee angle. Table 10 gives the definitions of each of these

three angles.

39

Table 10: Definitions of body angles.

 

Angle

Definition

 

Body Recline
Angle (BRA)

Angle between the vector from mid-ASIS location to the sternal notch
and the lab vertical in the sagittal planez.

 

Thorax Angle

Angle between the vector from the mid-stemum to the sternal notch and
the lab vertical in the sagittal planez.

 

Angle between the vector from the sitter’s HJC to the right ASIS and the

 

 

Pelv1c Angle lab horizontalz.
Knee An le Angle between the two vectors, one from the knee target to the thigh
g target and the other from the knee target to the lower leg targetz.

 

 

40

 

Body Recline Angle (BRA)
Based on the definition given in Table 10, Body Recline Angle (Figure 20) was
computed using the following equationzz
Equation 1: Computation of Body Recline Angle
Body Recline Angle = arcsin (By)
where By = y-component of unit vector from mid ASIS location to sternal notch; y axis

pointing anteriorly with respect- to the subject.

Figure 20: Body Recline Angle (BRA).

 

Zaxis

 

 

 

 

  
  
  

BRA

 

 

 

 

Stemal
notch target

 

 

 

 

ASIS targets

 

 

 

41

Thorax Angle
Based on the definition given in Table 10, thorax angle (Figure 21) was computed
using the following equationzz
Equation 2: Computation of thorax angle.
Thorax angle = arcsin (Ty)
where Ty = y-component of unit vector from mid-sternum to sternal notch; y axis

pointing anteriorly with respect to the subject.

Figure 21: Thorax angle.

 

Zaxis

 

 

 

 

Thorax
angle

 

 

 

 

Stemal notch

 

 

 

  
 

 

Mid sternum

 

 

 

42

Pelvic Angle

To calculate the pelvic angle, it was first necessary to compute the Hip Joint
Center (HJC) of each subject. This was done using the method described in a research
paper by Bush and Gutowskizb. Initially, the HI C of each subject was computed in the
reference file position. For this, each subject was asked to sit in an erect posture with
their knees positioned a comfortable distance apart. Using the three dimensional
coordinates of the right ASIS, left ASIS and mid-PSIS captured by the motion analysis
cameras, the Seidel method27 was used to get the corresponding x, y and z coordinates of
the H] C. Seidel determined the following percentages to locate the HJC relative to the
respective ASIS: 14% pelvic width (PW) medially, 34% pelvic depth (PD) posteriorly
and 79% pelvic height (PH) inferiorly.

With the computed initially accurate HJC location, two assumptions were
considered. The distance between the HI C and the lateral epicondyle knee target, and the
distance from the HI C to the right ASIS target would be assumed constant since both the
pelvis and femur were considered rigid bodies. Using coordinate data from the reference
files, the lengths of two vectors were computed: [1] from HJC to right knee (Lfemm) and
[2] from H] C to right ASIS (ch105). Now, with the subject seated as per the experiment
trial conditions of seat back recline and back support, it was required to compute the H] C
for each of those postures. This required solving equations that defined two spheres (as
shown in Figure 22) with constant radii equal to the computed length of the HJC to the
right ASIS and the HJC to the right knee. The x, y and z coordinates of the right ASIS
and the right knee were measured from target data. The medio-lateral position, or the x

coordinate of the H] C, was chosen as fixed position relative to the right ASIS and based

43

on pelvic width. This reduced the equations to the intersection of 2 circles. The z
coordinate of the H] C was then evaluated. The z coordinate had two possible solutions,
however one solution was located superiorly to the ASIS position and was discarded.

Next the y coordinate was calculated.

Equation 3: Computation of HJC using the Bush-Gutowski method“.

2 2 2 _ 2
(XHJc - xrightASlS) + (YHJC — YrightASlS) + (ZHJC - ZrightASlS) — Lpelvis

2 2 2 _ 2
(XHJC “ XriglitKnee) + (YHIC " YrightKnee) + (ZHJC — ZrightKnee) _ I-4femur

Figure 22: Determination of HJC of seated subject using the Bush-Gutowski
method“.

 

 

 

 

 

ASIS

 

 

 

dl‘----~‘
‘

 

 

 

 

 

 

 

I”pelvis

 

 

 

 

/ Knee

 

   

 

Mid PSIS

 

 

 

 

 

 

 

 

1 :-

, .

‘ _r

3 \ ; I
.' u. .

HJC - ~ - -n'
' ------ "
; 1
o

 

 

 

44

Knee Angle

The knee angle (Figure 23) was calculated by taking the dot product between two
vectors, one from the right knee target (A) to the right thigh target (B) and the other from
the right knee target to the right lower leg target (C). Hence, we have the following

equations:

Equation 4: Calculation of knee angle.
A=ali+agj+a3k, B=bli+b2j+b3k, C=cli+czj+c3k
DZA—B=d11+d3j+d3k, EZC—B=€|l+€1i+€3l(

D-E = IDl * IEI * cosine(0)

where 0 = angle between the two vectors (that is, knee angle)
D-E = (d1 *el) + (d2*e2) + (d3*e3)

IDI = ((112 + (122 + d32)l/2, IEI : (612 + 622 + 632)“2

Figure 23: Knee angle.

 

  
 

 

Knee target

 

 

 

 

 

 

“/4“ Lower leg

/ target

 

 

 

 

 

 

 

45

Lower Back Support Pad Position

There was a regular scale calibrated in millimeters attached to the seat back of the
experimental seat to determine the pad apex height above the seat pan. After each trial,
the subject was asked to step down from the chair and the height of the apex position line
on the lower back support pad was marked off using this scale. This height was
calculated at the same recline angle as the seat back. The fore-aft prominence of the
support pad was measured using an L—shaped scale. One arm of this scale helped to get
the fore—aft prominence, while the other assisted in ensuring accurate leveling

measurement for height above seat pan (Figure 24).

Figure 24: Measurement of subject-selected position of lower back support
using L-scale.

 

46

Force Data

Two force transducers used in Phase 2 testing, one for the upper back (thoracic)
support and the other for the lower back support. The thoracic support was positioned at
the seventh thoracic vertebra (T7) for all subjects while the lower back support was
moveable and was positioned by each subject individually as per their desired comfort.

Each of the two force transducers was mounted such that the X axis pointed
inferiorly, the Y axis pointed left lateral and the Z axis pointed normal to the surface of
the force plate. An initial reference file was taken with the experimental seat unloaded
and upright seat back condition. This was done for each of the three lower back support
pads. LabView 7.1 software was used to collect the F,, F y, and F2 force data values in this
condition for both the transducers. Since these force values were in the upright seat back
condition (0° recline with respect to vertical), it was required for them to be converted to
values corresponding to each of the 4 recline angles, 10°, 15°, 20° and 24°, being tested
in Phase 2 (Figure 25). For this a transformation matrix was used which yielded

- 2
equations as shown below .

47

Figure 25: Conversion of reference force data from reference upright position to test
recline position.

 

 

 

 

 

v
.3”

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fz'

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fx'

 

 

 

Equation 5: Equations for conversion of reference force data from reference upright
position to test recline position.

 

Fx' = (Fx*cose) - (Fz*sin0)

Fy' = Fy
Fz' = (Fx*sin0) + (Fz'cose)

0 = 10°, 15°, 20°, 24°

 

 

 

The transformed values were then either subtracted from or added to the force

data values collected during the test trials for each recline angle.

48

Statistical Data Analysis

Data obtained from this research were broadly classified into three categories for
analyses: body angles, back support pad positions and force data on both thoracic and
lower back supports.

A One Way Repeated Measures Analysis Of Variance (RM ANOVA) statistical
test was performed to compare:

1.) The effects of each pad on thorax, body recline, pelvic and knee angles of all
subjects (n = 18).

2.) The respective pad positions in terms of apex height above seat pan and apex
fore-aft prominence at each of the four recline angles tested taking all subjects into
consideration (n = 18).

3.) The normal, vertical shear and lateral shear forces exerted on both the thoracic
and lower back supports for all subjects (n = 18).

For each of the three categories of comparisons mentioned above, a Mann-
Whitney Rank Sum statistical test was also performed to compare results between the
three anthropometric subject groups tested in Phase 2. Since these comparisons involved
two different subject groups along with variation in number of subjects in each group, a
Mann- Whitney Rank Sum test was considered more stringent than a paired t-test. The
level of statistical significance was set at p=0.05 for all analyses. Wherever statistical
significance was reached, a Tukey post hoc analysis was performed to determine

differences between individual groups.

49

Data Results

Body Angles
Body Recline Angle (BRA)

Tables 11 and 12 provide the BRA of all 18 subjects. Table 11 lists data
corresponding to the office seating recline angles while Table 12 provides similar data for
the vehicle seating recline angles. Angles achieved by subjects tested with all three pads
have been given at each recline angle.

The BRA is a measure to compare the angle of the torso to that of the seat back.
In most cases we observe the average BRA values given in Tables 11 and 12 are a few
degrees more than the seat back recline angle. This shows that even though appropriate
steps are taken (use of rectangular board) to ensure that the subjects sit erect in the
experimental seat, they do tend to slip once the seat back recline angles are changed. This
could be due to the material properties of the fabric covering the thorax support and the
seat pan. Another likely reason could be the positioning of the lower back support

causing a force to be applied onto the lower back region of the subject.

50

Table 11: Body Recline Angles of all 18 subjects in the office seating test
environment. All values are in degrees. Negative sign indicates rearward of vertical.
SD = Standard Deviation.

 

Subject ID 10° 15°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -I4.l -l3.1 -l4.7 -19.0 -18.0 -18.8
P23 -5.4 -6.1 —7.3 -l2.3 -l 1.1 -12.3
P2C —8.0 -9.1 -8.1 -9.1 -9.0 -l3.3
P2D -14.9 -12.3 -l3.7 -15.3 -l3.3 ~15.2
P2E -9.6 -6.1 -6.0 —l4.5 ~12.9 -1 1.0
P2F -9.3 -4.5 -6.4 -l4.8 -6.2 —10.l
PZG —ll.0 -7.9 —8.7 -15.5 -15.6 -15.3
P2H -l7.7 -12.7 -l3.5 -21.2 -l6.2 -18.8
P2I -l7.2 -15.3 -15.0 -22.2 -22.9 -22.0
P2J -ll.2 -ll.7 -ll.7 -12.7 -ll.7 -12.0
Avg -1 1.8 -9.9 -10.5 -15.7 -l3.7 -14.9
SD 4.0 3.6 3.6 4.1 4.8 3.9

5th percentile

females
P2K -15.0 -l4.l -IS.2 -20.7 -l7.9 ~18.7
P2L -15.5 -12.3 —9.4 -22.0 -18.7 —l6.6
P2M -15.4 -l3.9 -12.6 -20.6 -l7.3 -l9.5
P2N -23.7 -I9.2 -16.5 -24.7 -22.3 -21.2
Avg -l7.4 -14.9 -13.4 -22.0 -l9.1 -19.0
SD 4.2 3.0 3.1 1.9 2.2 1.9

95th percentile

males
P2U -15.2 -l4.7 -l3.6 -18.l -l7.1 -18.0
P2V -l7.7 -l9.8 —l9.6 -23.9 -22.7 -24.8
P2W -l 1.8 -lO.5 -l3.5 -l7.3 -l4.9 -16.0
P2X -ll.3 -12.6 -lO.7 -12.3 -l3.8 -ll.1
Avg -14.0 -l4.4 -l4.3 -l7.9 -17.1 -17.5
SD 3.0 4.0 3.8 4.8 4.0 5.7
Total Avg —l3.6 —12.0 ~12.0 -17.6 —15.7 -'16.4
SD 4.3 4.2 3.8 4.5 4.6 4.2

 

51

Table 12: Body Recline Angles of all 18 subjects in the vehicle seating test
environment. All values are in degrees. Negative sign indicates rearward of vertical.
SD = Standard Deviation.

 

Subject ID 20° 24°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -22.5 -21.1 -22.2 -27.9 -29.3 -26.1
PZB -l4.5 -l4.4 -l7.l -22.2 -l7.6 -20.0
P2C -l3.3 -12.l -I3.0 -2l.l -17.4 ~18.1
P2D -20.7 -l9.5 -15.1 24.3 -20.6 -l9.7
P2E -17.9 -l3.2 -l7.5 -23.5 -l9.5 -2l.9
P2F -l9.7 -l8.0 -l6.2 -25.4 -22.3 -23.6
P2G -15.9 -l9.4 -l7.2 -24.9 -24.3 -24.0
P2H -22.5 -17.6 -l8.4 -26.5 -22.3 -23.9
P21 -24.7 -24.6 -23.4 -28.2 -28.1 -30.4
P2J -l8.4 -18.6 -22.0 -22.4 -22.7 -22.2
Avg -19.0 -17.9 -18.2 -24.6 -22.4 -23.0
SD 3.7 3.8 3.3 2.4 4.0 3.5
5th percentile
females
P2K -22.1 -21.5 -l8.4 -28.4 —25.6 -27.6
P2L -23.4 -23.6 -23.6 -28.3 -28.5 -28.4
P2M -22.7 -l9.3 -20.8 -26.0 -22.0 -22.8
P2N -20.6 -18.7 -15.6 -25.4 -22.4 -20.5
Avg -22.2 -20.8 -l9.6 -27.0 -24.6 -24.8
SD 1.2 2.2 3.4 1.6 3.0 3.8
95th percentile
males
P2U -20.6 -18.7 -21.3 -25.0 -24.6 -27.9
P2V -30.2 -30.2 -32.2 ~35.0 -35.3 -36.9
P2W -19.2 -20.5 -20.7 —23.9 -25.3 -24.0
P2X -22.7 -20.3 -19.7 -24.6 -26.3 -23.7
Avg -23.2 -22.4 -23.5 -27.1 -27.9 —28.1
SD 4.9 5.2 5.8 5.3 5.0 6.2
Total Avg -20.6 -19.5 -19.7 -25.7 -24.1 -24.5
SD 3.9 4.2 4.3 3.2 4.4 4.5

 

52

Table 13 summarizes the results of the statistical tests performed on the data

presented in Tables 1 l and 12. The bolded p-values indicate significant differences.

Table 13: Summary of p-values of statistical tests performed for the comparison of
the effect of each pad on Body Recline Angles at each seat back recline angle. Values
in bold indicate significance (n = 18).

 

Pad 1 v Pad 2
Pad 2 v Pad 3
Pad 1v Pad 3

 

Recline Angles
10° 15° 20°
0.013 0.002 0.409
1.000 0.338 0.904
0.014 0.063 0.492

24°

0.007
0.673
0.057

 

 

From Tables I l and 12, the Total Average values indicate the maximum BRA

was being produced by the subjects when they interacted with Pad 1 as compared to the

other two pads. Statistical results from Table 13 indicate the Pad 1 results vary

significantly when compared with both Pads 2 and 3. Even in the cases where no

statistical significance is observed in comparisons involving Pad 1 (that is, when

comparing Pad 1 with Pad 3 at 15° and 240 recline angles), the p-values are only slightly

greater (0.063 and 0.057 respectively) than the maximum p-value (0.05) defined for

achieving significance.

Tables 14 and 15 provide a summary of the statistical p-values computed from the

comparisons made between each anthropometric group using each lower back support

pad at all recline angles. Table 14 provides data corresponding to the office seating

recline angles while Table 15 provides similar data for the vehicle seating recline angles.

53

Table 14: Summary of p-values from statistical tests to compare BRA of each
anthropometric group individually for office seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.040 0.032 0.181 0.013 0.055 0.071
SF v LM 0.343 0.855 0.718 0.160 0.430 0.629
MM v LM 0.356 0.063 0.098 0.392 0.227 0.340

 

 

Table 15: Summary of p-values from statistical tests to compare BRA of each
anthropometric group individually for vehicle seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4).

 

 

Anthropometric 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.125 0.178 0.498 0.095 0.341 0.406
SF v LM 0.712 0.584 0.296 0.972 0.309 0.397
MM v LM 0.107 0.090 0.052 0.235 0.051 0.069

 

 

From Tables 14 and 15 we observe that even though there are only three cases
where significant differences are computed (MM v SF in office seating, Table 14),
however there are several p-values being only slightly greater than 0.05. This is
especially observed in comparisons involving the 5‘h percentile females (SF)
anthropometric group. Such Observances are made when comparing SF with MM in the
office seating tests; however, in the vehicle seating tests, it is the comparisons of SF with

the MM anthropometric group that show similar trends.

54

Thorax Angle

Tables 16 and 17 provide the thorax angles of all 18 subjects. Table 16 lists data
corresponding to the office seating recline angles while Table 17 provides similar data for

the vehicle seating recline angles. Angles achieved by subjects tested with all three pads

have been given at each recline angle.

55

Table 16: Thorax angles of all 18 subjects in the office seating test environment. All
values are in degrees. Negative sign indicates rearward of vertical. SD = Standard
Deviation.

 

Subject ID 10° 15°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -30.4 -27.6 -28.6 -33.2 -32.4 -32.9
PZB -15.9 -l6.6 -I9.I -l9.4 —20.7 —20.9
P2C -20.1 -24.5 -23.4 -25.5 -23.7 -29.2
P2D -l6.2 -l7.9 -19.3 -20.0 —20.8 -23.4
P2E -2l.2 -20.6 ~18.6 -23.2 -26.1 -22.8
P2F -22.3 -22.1 -24.1 -28.4 -24.2 -26.3
P2G -23.9 -l9.l -21.0 -27.5 —25.1 -26.8
PZH -34.7 -32.0 -31.4 -37.7 -33.0 -35.9
P21 -30.0 -31.9 -32.3 —35.0 -35.7 —36.6
P2J -32.1 -34.2 -32.9 -32.9 -33.7 -31.4
Avg -24.7 -24.6 -25.1 -28.3 -27 .5 -28.6
SD 6.7 6.4 5.8 6.3 5.6 5.5
5th percentile
females
P2K -36.5 -34.5 -34.1 -40.6 -34.7 —35.8
P2L -33.1 —33.5 -32.9 -33.3 —32.6 -36.3
P2M -45.0 -42.0 -41.6 -47.0 -43.9 -46.0
P2N -49.4 —41.8 —41.8 -49.5 —49.3 —47.4
Avg -41.0 -38.0 -37.6 -42.6 -40.1 -41.4
SD 7.5 4.6 4.7 7.2 7.8 6.2
95th percentile
males
P2U -40.0 -37.6 -35.3 -4l.l -36.7 -37.2
P2V —42.1 -44.3 -41 .1 -46.8 -43.4 -45.0
P2W -23.9 -22.1 -24.4 -28.2 -27.0 -25.6
P2X -27.4 -30.3 -28.2 -28.1 -3 1.5 -28.6
Avg -33.3 -33.6 -32.2 -36.0 -34.6 -34.1
SD 9.0 9.5 7.4 9.4 7.0 8.8
Total Avg -30.2 -29.6 -29.5 -33.2 -3 1.9 —32.7
SD 9.8 8.7 7.7 9.1 8.1 8.0

 

56

Table 17: Thorax angles of all 18 subjects in the vehicle seating test environment.
All values are in degrees. Negative sign indicates rearward of vertical. SD =
Standard Deviation.

 

Subject ID 20° 24°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -35.1 -33.6 —36.1 -39.0 -40.3 -37.9
PZB -25.9 -26.0 -28.0 -32.0 -27.7 28.6
P2C -24.8 -26.1 -25.0 -3 1.6 —29.2 -29.6
PZD -26.0 -27.0 -30.0 -29.8 -28.2 -26.0
P2E -34.9 -31.9 -34.1 40.0 -35.2 —37.6
P2F -40.4 -36.5 -35.9 —43.4 -39.8 -42.3
P2G -24.7 -24.9 -24.5 -3 l .8 -32.5 -3 l .6
P2H —40.4 -35.9 -40.2 ~41 .6 —25.4 -39.8
P21 -37.6 41.4 -38.0 -41.1 -4l.l -40.7
P2J —41.3 -39.8 -42.5 42.4 —42.0 -42.7
Avg -33.1 -32.3 -33.4 ~37.3 -34.1 -35.7
SD 7.0 6.1 6.3 5.3 6.3 6.2
5th percentile
kmflw
P2K -40.9 -38.2 -36.0 -46.9 —41.9 45.3
P2L —40.5 -4l.l -42.5 -42.2 -42.3 -40.0
P2M ~52.2 -50.2 -50.2 —55.0 -52.3 -51.5
P2N -50.0 -51.1 -55.4 ~54.1 -57.1 -52.8
Avg -45.9 -45.1 -46.0 —49.6 -48.4 -47 .4
SD 6.0 6.5 8.5 6.1 7.5 5.9
95th percentile
males
P2U —49.8 —41.3 -44.4 -44.5 -42.2 -46.3
P2V -51.6 -51.9 -52.6 -55.6 -55.0 -56.8
P2W -30.3 -3 1.0 -30.9 -33.2 -35.3 -33.7
P2X -38.7 -38.5 -34.6 -38.8 -42.7 -39.5
Avg -42.6 -40.7 -40.6 -43.0 -43.8 -44.1
SD 10.0 8.7 9.8 9.5 8.2 9.9
Total Avg -38.1 -37.0 -37.8 -4l.3 —39.5 -40.2
SD 9.2 8.5 8.9 8.0 9.1 8.5

 

57

Table 18 summarizes the results of the statistical tests performed on the data

presented in Tables 16 and 17. The bolded p-values indicate significant differences.

Table 18: Summary of p-values of statistical tests performed for the comparison of
the effect of each Pad on thorax angles at each seat back recline angle. Values in
bold indicate significance (n = 18).

 

 

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.836 0.660 0.726 0.506
Pad 2 v Pad 3 0.960 0.780 0.783 0.814
Pad 1 v Pad 3 0.792 0.858 0.939 0.683

 

The Total Average values from Tables 16 and 17 indicate a steady increase thorax
angles with increase in seat back recline angle. However, no statistical significance is
seen for any of the comparisons listed in Table 18.

Tables 19 and 20 provide a summary of the statistical p-values computed by
comparing each anthropometric group using each lower back support pad. Comparisons
have been made at all four recline angles. Table 19 provides data corresponding to the

office seating recline angles while Table 20 provides similar data for the vehicle seating.

58

Table 19: Summary of p-values from statistical tests to compare thorax angles of

each anthropometric group individually for office seating. Values in bold indicate

significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.002 0.003 0.002 0.003 0.005 0.003
SF v LM 0.241 0.440 0.271 0.312 0.339 0.224
MM v LM 0.070 0.062 0.074 0.094 0.069 0.178

 

 

Table 20: Summary of p-values from statistical tests to compare thorax angles of
each anthropometric group individually for vehicle seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5’” percentile females (n=4),
LM = 95'“ percentile males (n=4).

 

Anthropometric 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.008 0.004 0.010 0.003 0.004 0.007
SF v LM 0.593 0.439 0.438 0.294 0.440 0.586
MM v LM 0.064 0.060 0.123 0.168 0.035 0.075

 

 

 

Results from Tables 19 and 20 indicate significant differences in comparisons
involving the 50m percentile males (Mid Males, MM) anthropometric group. In
comparisons between the MM and SF (Small Females, 5‘h percentile) anthropometric
groups, p-values are well below the 0.05 mark in both office and vehicle seating tests;
while, in comparisons between the MM and LM (Large Males, 95th percentile) groups,
there are several cases of p-values being only slightly greater than the 0.05 mark for
significance. Numerical data from Tables 16 and 17 indicate that thorax angle values for
the MM group are much lower than those compared to the SF and LM anthropometric

groups.

59

Pelvic Angle

Tables 21 and 22 provide the thorax angles of all 18 subjects. Table 21 lists data
corresponding to the office seating recline angles while Table 22 provides similar data for
the vehicle seating recline angles. Angles achieved by subjects tested with all 3 pads have

been given at each recline angle.

60

Table 21: Pelvic angles of all 18 subjects in the office seating test environment. All
values are in degrees. Negative sign indicates anterior relative to horizontal. SD =
Standard Deviation.

 

Subject ID 10° 15°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

males
P2A -6l.6 -70.8 -78.3 -65.0 -74.2 -83.5
P2B -54.2 -55.3 -51.2 -48.7 -55.1 -52.7
P2C -48.2 -40.2 -56.6 -38.8 -6l.9 ~45.7
P2D -l 7.7 -25.4 -l6.3 -l7.l -40.1 -32.9
P2E -63.3 -52.3 -54.9 -50.0 -57.4 -55.6
P2F -l7.9 -30.4 -35.0 -35.5 -40.3 -39.4
P2G —46.7 —45.1 —49.0 —46.8 -49.6 -56.3
P2H -46.6 -47.0 -52.4 -53.6 -53.4 486
P21 -22.3 -28.8 -36.4 -48.4 47.0 —58.7
P2J -28.9 -25.3 -35.2 -30.9 -37.4 -41.0
Avg -40.7 -42.1 -46.5 -43.5 -51.7 -51.4
SD 17.6 15.0 16.7 13.4 11.3 14.0

5th percentile
females
P2K -74.8 -73.1 -78.3 -73.6 -8l.2 -79.8
P2L -21.6 -37.4 -37.8 -29.8 -32.8 444.7
P2M -50.3 -57.9 -54.2 -48.8 -59.2 -60.4
P2N -58.2 -63.5 -56.4 -39.3 -69.1 -66.5
Avg —51.2 -58.0 -56.7 -47.8 -60.6 -62.9
SD 22.2 15.1 16.6 18.8 20.6 14.6
95th percentile

males
P2U -60.6 -62.0 -59.5 -62.9 -57.8 -60.7
P2V -33.7 -34.3 -42.6 48.3 -47.1 —49.8
P2W -79.3 -72.7 -77.3 -82.8 520.6 -79.1
P2X -34.5 -44.8 -49.3 -35.3 -22.8 -30.6
Avg -52.0 -53.4 -57.2 -57.3 -52.1 -55.0
SD 22.0 17.2 15.1 20.4 24.0 20.3
Total Avg -45.6 -48.1 -51.1 -47.5 -53.7 -54.8
SD 19.2 16.2 16.3 16.2 16.1 15.3

 

 

 

61

Table 22: Pelvic angles of all 18 subjects in the vehicle seating test environment. All
values are in degrees. Negative sign indicates anterior relative to horizontal. SD =
Standard Deviation.

 

Subject ID 20° 24°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -79.4 -73.1 -8 l .8 -7l .6 -70.8 -80.6
PZB -49.6 -47.5 -50. I —53.3 -56.2 -49.9
P2C -48.4 -56.6 -51.8 -55.9 -54.3 -58.6
PZD -38.7 -45.9 -33.1 —30.5 —38.6 -23.3
P2E —46.4 ~51 .3 -33.6 —53.4 -44.0 -3 1.5
P2F -42.1 -42.5 —44.9 —44.5 -56.4 -51.4
P2G -6l .3 -63.4 -56.8 -65.4 -56.5 -63.4
P2H -59.2 -51.6 —43.4 -45.8 -39.7 -57.9
P21 -39.8 -32.3 -52.1 -58.4 -46.7 -54.9
P2] -45.3 —49.6 -42.0 -44.3 -53.2 -53.0
Avg -51.0 -51.4 -49.0 -52.3 -51.6 -52.4
SD 12.5 11.2 13.9 11.7 9.7 15.9

5th percentile
females
P2K -84.2 -77.6 -86.3 -76.9 -78.2 -77.3
P2L —42.9 -51.9 -63.2 -59.5 —47.8 -52.1
P2M ~54.9 -57.7 -58.9 -53.8 -57.7 -57.7
P2N -73.8 -63.1 -67.7 -73.9 —68.6 -72.8
Avg -64.0 -62.6 -69.0 -66.0 -63.1 -65.0
SD 18.6 11.0 12.1 11.1 13.2 12.0
95th percentile

males
P2U -57.0 -50.8 -57.1 -63.2 -60.7 -65.0
P2V -6l .6 -64.7 -69.0 —71.8 -74.2 -69.4
P2W -83.8 -79.5 -81.0 -77.7 -72.6 -74.2
P2X -40.8 -23.6 -35.1 -34.7 -34.9 -29.1
Avg -60.8 -54.6 -60.5 -61.8 —60.6 -59.4
SD 17.7 23.8 19.6 19.1 18.2 20.6
Total Avg -56.1 -54.6 -56.0 -57.5 -56.2 -56.8
SD 15.3 14.4 16.4 14.0 12.9 16.2

 

62

Table 23 summarizes the results of the statistical tests performed on the data
presented in Tables 21 and 22. The bolded p-values indicate significant differences. No

numerical pattern or statistical trend is observed from results provided in Tables 21, 22

and 23.

Table 23: Summary of p-values of statistical tests performed for the comparison of
the effect of each pad on pelvic angles at each seat back recline angle. Values in bold
indicate significance.

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.304 0.258 0.768 0.773
Pad 2 v Pad 3 0.192 0.842 0.788 0.901
Pad 1 v Pad 3 0.007 0.178 0.989 0.891

 

 

 

Statistical p-values computed by comparing each anthropometric group using
each lower back support pad at all 4 recline angles have been provided in Tables 24 and
25. Table 24 provides data corresponding to the office seating recline angles while Table

25 provides similar data for the vehicle seating recline angles.

63

Table 24: Summary of p-values from statistical tests to compare pelvic angles of
each anthropometric group individually for office seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),

LM = 95th percentile males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.366 0.098 0.325 0.628 0.309 0.197
SF v LM 0.961 0.706 0.966 0.521 0.610 0.555
MM v LM 0.330 0.239 0.293 0.155 0.963 0.706

 

 

Table 25: Summary of p-values from statistical tests to compare pelvic angles of
each anthropometric group individually for vehicle seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4).

 

Anthropometric 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.151 0.1 16 0.067 0.069 0.095 0.185
SF v LM 0.814 0.568 0.489 0.718 0.833 0.657
MM v LM 0.260 0.725 0.23] 0.269 0.243 0.289

 

 

 

Results from Tables 24 and 25 indicate no significant results under all conditions
of recline. This goes to show that variation in subject anthropometry does not

significantly vary the pelvic angles achieved.

64

Knee Angle

Tables 26 and 27 provide the knee angles of all 18 subjects. Table 26 lists data
corresponding to the office seating recline angles while Table 27 provides similar data for
the vehicle seating recline angles. Angles achieved by subjects tested with all three pads

have been given at each recline angle

65

Table 26: Knee angles of all 18 subjects in the office seating test environment. All
values are in degrees. SD = Standard Deviation.

 

 

 

Subject ID 10° 15°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
50th percentile
males
P2A 120.2 124.0 125.9 123.8 127.2 130.1
P2B 132.6 131.6 133.5 135.1 135.0 131.7
P2C 133.3 131.4 135.1 133.1 133.9 138.6
P2D 128.9 129.6 124.5 129.8 131.6 126.9
P2E 120.7 118.4 119.8 124.1 122.1 124.7
P2F 125.5 128.6 125.7 127.4 128.7 128.8
P2G 120.9 125.1 123.1 126.8 124.5 126.8
P2H 135.7 137.2 140.5 138.6 142.4 137.2
P21 121.8 121.6 121.4 120.6 122.2 121.4
P2J 140.4 126.5 133.9 130.9 128.5 142.8
Avg 128.0 127.4 128.3 129.0 129.6 130.9
SD 7.2 5.5 6.9 5.6 6.3 6.7
5th percentile
females
P2K 135.2 138.8 133.4 130.3 144.9 139.5
P2L 145.1 134.7 l3l.4 140.6 138.8 129.0
P2M 122.1 123.7 124.0 123.4 126.0 125.9
PZN 127.5 144.4 122.0 118.2 138.9 131.4
Avg 132.5 135.4 127.7 128.1 137.2 131.5
SD 10.0 8.8 5.6 9.7 8.0 5.8
95th percentile
males
P2U 132.5 134.1 128.5 132.1 129.7 131.6
P2V 124.7 122.3 120.0 129.4 121.9 123.3
P2W 127.7 119.2 115.8 124.1 123.4 117.1
P2X 122.4 122.1 122.4 122.3 124.4 126.4
Avg 126.8 124.4 121.7 127.0 124.9 124.6
SD 4.4 6.6 5.3 4.5 3.4 6.0
Total Avg 128.7 128.5 126.7 128.4 130.2 129.6
SD 7.3 7.3 6.6 6.1 7.3 6.6

 

66

Table 27: Knee angles of all 18 subjects in the vehicle seating test environment. All
values are in degrees. SD = Standard Deviation.

 

 

Subject 1D 20° 24°
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
50th percentile
males
PZA 150.3 155.0 154.5 155.3 156.9 157.4
PZB 159.2 159.5 156.5 160.9 161.8 160.1
P2C 161.5 161.4 162.4 162.7 162.6 163.0
P2D 150.8 148.6 153.5 152.9 151.4 150.9
P2E 145.2 149.4 143.2 147.1 150.3 148.6
P2F 148.5 149.6 150.4 151.6 152.1 154.9
PZG 146.9 146.1 145.9 148.1 148.8 146.3
PZH 166.6 165.9 166.3 167.6 167.8 165.9
P21 135.4 137.1 141.8 139.5 142.1 135.8
P2J 148.4 148.4 148.4 149.0 150.4 148.3
Avg 151.3 152.1 152.3 153.4 154.4 153.1
SD 9.0 8.4 8.0 8.4 7.7 9.0
5th percentile
females
P2K 151.0 153.0 151.0 152.8 152.5 152.0
P2L 150.7 151.6 151.3 152.0 150.6 150.4
P2M 147.2 145.6 146.4 150.8 148.9 152.3
P2N 146.4 142.5 139.1 148.3 146.4 143.6
Avg 148.8 148.2 147.0 151.0 149.6 149.6
SD 2.4 4.9 5.7 2.0 2.6 4.1
95th percentile
males
P2U 154.0 154.3 153.3 154.1 154.4 153.7
P2V 154.7 155.6 154.4 155.7 155.6 156.2
P2W 149.2 149.6 151.2 153.2 154.2 154.4
P2X 147.8 147.4 148.4 147.9 148.1 150.9
Avg 151.4 151.7 151.8 152.7 153.1 153.8
SD 3.4 3.9 2.6 3.4 3.4 2.2
Total Avg 150.8 151.1 151.0 152.7 153.0 152.5
SD 6.9 6.9 6.8 6.4 6.2 7.0

 

 

67

Table 28 summarizes the results of the statistical tests performed on the data

presented in Tables 26 and 27. The bolded p-values indicate significant differences.

Table 28: Summary of p-values of statistical tests performed for the comparison of
the effect of each Pad on knee angles at each seat back recline angle. Values in bold

indicate significance.

 

Pad 1 v Pad 2
Pad 2 v Pad 3
Pad 1v Pad3

 

Recline Angles
10° 15° 20°
0.929 0.411 0.870
0.441 0.796 0.950
0.390 0.559 0.764

24°

0.887
0.799
0.906

 

 

The Total Average values at the bottom of Table 26 indicate similar results for the

two office seating recline angles of 10° and 15°. Likewise, the Total Average values from

Table 27 (vehicle seating) also show similarity. There is however an appreciable

difference in knee angle values between the office and vehicle seating environments,

vehicle seating resulting in much larger angles. No statistical significance is observed in

any of the comparisons provided in Table 28.

Tables 29 and 30 provide a summary of the statistical p-values computed from the

comparisons made between each anthropometric group using each lower back support

pad at all recline angles. Table 29 provides data corresponding to the office seating

recline angles while Table 30 provides similar data for the vehicle seating recline angles.

68

Table 29: Summary of p-values from statistical tests to compare knee angles of each
anthropometric group individually for office seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95th percentile males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.364 0.058 0.872 0.829 0.084 0.889
SF v LM 0.340 0.092 0.168 0.837 0.059 0.154
MM v LM 0.770 0.400 0.110 0.529 0.186 0.131

 

 

Table 30: Summary of p-values from statistical tests to compare knee angles of each
anthropometric group individually for vehicle seating. Values in bold indicate
significance. MM = 50th percentile males (n=10), SF = 5th percentile females (n=4),
LM = 95"1 percentile males (n=4).

 

 

Anthropometric . 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.608 0.407 0.251 0.575 0.255 0.471
SF v LM 0.259 0.302 0.171 0.405 0.153 0.118
MM v LM 0.976 0.935 0.913 0.869 0.748 0.995

 

 

Results from Tables 29 and 30 indicate no significant results under all conditions
of recline. This shows that variation in subject anthropometry does not significantly vary
the knee angles achieved although knee angles in the vehicle seating environment are

much greater than those in the office seating environment.

69

Lower Back Support Pad Position
Height

Tables 31 and 32 provide the numerical data values of the apex height of each pad
above the seat pan for all 18 subjects. Averages have been calculated for each
anthropometric group individually as well as for all subjects together. Table 31 lists data
corresponding to the two office seating recline angles of 10° and 15° while Table 32 lists
similar data for the vehicle seating recline angles of 20° and 24°. The vertical height of
L3 above the seat pan has also been listed for each subject in both Tables. Figure 26

shows the measurement of pad apex height along the plane of the seat back.

Figure 26: Method of measurement of lower back support pad apex height above
seat pan.

 

Seat back

 

 

 

 

Supp ort pad apex height
position

 

 

 

   

 

Seat pan

 

 

 

./

 

A.

Pad apex height
above seat pan

 

 

 

 

 

 

 

 

70

Table 31: Numerical data values of support pad apex height above seat pan for
office seating. All values are in mm.

 

 

Subject 10°

ID Pad 1 Pad 2

50th percentile males

P2A 205 196
PZB 120 1 12
P2C 121 127
P2D 178 165
P2E 178 206
P2F 207 200
P2G 185 190
P2H 161 159
P21 123 120
PZJ 182 188
Avg 166 166
5th percentile females
P2K 205 202
P2L 162 149
P2M 177 169
P2N 158 189
Avg 175 177
95th percentile males

P2U 190 186
P2V 207 204
P2W 195 203
P2X 223 245
Avg 204 209
Total 176 178
Avg

SD 31 34

Pad 3

197
117
133
150
181
201
180
150
134
173

161
173
149
180
168
167
162
176
174
217

182

167

25

Pad 1

184
155
174
150

165
175
194
189
213

193

169

35

15°
Pad 2

180
155
158
183

169
170
196
207
220

198

181

35

Pad 3

206
100
181
158
188
224
162
144
67
183

161
176
143
147
142
152
149
160
185
177

168

160

36

Height

of L3

above
seat nan

176
231
197
168
170
172
228
221
225
189

198

183
182
154
182

176
257
250
239
187

233

Seated
Height

864
953
895
876
889
902
914
914
889
902

900

813
787
762
787

1016
978
1003
997

999

 

71

 

Table 32: Numerical data values of support pad apex height above seat pan for
vehicle seating. All values are in mm.

 

 

Subject 20°
ID Pad 1 Pad 2
50th percentile males
P2A 180 213
P2B 125 120
P2C 133 163
P2D 177 154
P2E 197 211
P2F 185 176
P2G 189 199
P2H 147 179
P21 154 155
P2J 193 194
Avg 168 176
5th percentile females
P21( 182 148
P2L 151 133
P2M 157 178
P2N 194 205
Avg 171 166
95th percentile males
P2U 181 186
P2V 223 215
P2W 186 189
P2X 231 245
Avg 205 209
Total 177 181
Avg
SD 28 32

Pad 3

194
71

165
135
192
163
180
161
136
182

158

181

141
174

142
139
160
163
199

165

156

36

Pad 1

199
93
95
171
210
228
190
131
157
189

166
150
135
165
197
162
184
203
180
225

198

172

39

24°
Pad 2

221
109
115
171
214
126
206
161
137
198

166
138
131
169
218
164
181
212
182
242

204

174

41

Pad 3

174
73 -
139
163
194
183
168
156
94
165

124
96

139
169

132
168
154
158
200

170

151

35

Vertical
height of
L3 above
seat pan

176
231
197
168
170
172
228
221
225
189

198

183
182
154
182

176
257
250
239
187

233

Seated
Height

864
953
895
876
889
902
914
914
889
902

900

813
787
762
787

787
1016
978
1003
997

999

 

72

 

Table 33 provides the numerical data values of support pad apex height above
seat pan for the office seating recline angles in terms of percentage of Seated Height (SH)
for each subject. Table 34 presents similar data corresponding to the vehicle seating
recline angles.

Average percentages from both Tables 33 and 34 indicate a narrow range of
results, the maximum percentage being 22% and minimum being 17% in both Tables.
This indicates that even with variation in seat back recline angles, subjects are able to
maintain a relatively constant relationship in terms of the position on the lower back
support pads with respect to the subject’s seated height. Figure 27 shows the

measurement of Seated Height pictorially.

Figure 27: Equivalence of Seated Height (SH) in erect and inclined seated

 

 

 

 

 

 

 

 

 

 

 

conditions.
”it” (\
Seated

Height *1
‘1 Seated
\ Height

‘ .

1
1_

 

73

Table 33: Support pad apex height expressed in terms of subject’s Seated Height
(SH) for office seating. SH is measured in millimeters. All other values are in

percentage. SD = Standard Deviation.

 

 

Subject
ID

50th
percentile
males
P2A
P2B
P2C
P2D
P2E
P2F
PZG
P2H
P21
P21

Avg
SD

5th
percentile
females
P2K
P2L
P2M
P2N

Avg
SD

95th
percentile
males
P2U
PZV
P2W
P2X

Avg
SD

Seated
Height
(SH)

864
953
895
876
889
902
914
914
889
902

900
24

813
787
762
787

787
21

1016
978
1003
997

999
1 6

10°
Pad] Pad2 Pad3 Pad]
24 23 23 21
13 12 12 9
14 14 15 16
20 19 17 20
20 23 20 20
23 22 22 25
20 21 20 21
18 17 16 15
14 13 15 12
20 21 19 21
18 19 18 18
4 4 3 5
25 25 21 23
21 l9 19 20
23 22 24 23
20 24 21 19
22 22 21 21
2 3 2 2
19 18 16 17
21 21 18 20
19 20 17 19
22 25 22 21
20 21 18 19
2 3 2 2

15°
Pad 2

27
12

20
23
27
20
19
12
21

22
20
21

23

17
20
21
22

Pad 3

24
10

18
21
25
18
16

20

22
18
19
18

15
16
18
18

 

74

 

Table 34: Support pad apex height expressed in terms of subject’s Seated Height
(SH) for vehicle seating. SH is measured in millimeters. All other values are in
percentage. SD = Standard Deviation.

 

 

Subject Seated 20° 24°
ID Height Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
(SH)
50th
percentile
males
P2A 864 21 25 22 23 26 20
P2B 953 13 13 7 10 . 11 8
P2C 895 15 18 18 1 1 13 15
P2D 876 20 18 15 20 20 19
P2E 889 22 24 22 24 24 22
P2F 902 21 20 18 25 14 20
P2G 914 21 22 20 21 22 18
P2H 914 16 20 18 14 18 17
P21 889 17 17 15 18 15 1 1
P2J 902 21 21 20 21 22 18
Avg 900 19 20 18 19 18 17
SD 24 3 4 4 5 5 4
5th
percentile
females
P2K 813 22 18 22 18 17 15
P2L 787 19 17 9 17 17 12
P2M 762 21 23 19 22 22 18
P2N 787 25 26 22 25 28 21
Avg 787 22 21 18 21 21 17
SD 21 2 4 6 4 5 4
95th
percentile
males
P2U 1016 18 18 14 18 18 16
P2V 978 23 22 16 21 22 16
P2W 1003 18 19 16 18 18 16
P2X 997 23 25 20 23 24 20
Avg 999 21 21 17 20 20 17
SD 16 3 3 3 2 3 2

 

75

 

Table 35 summarizes the results of the statistical tests performed on the data

presented in Tables 31 and 32. The bolded p-values indicate significance.

Table 35: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex heights above seat pan (n=18). Values in bold
indicate significance.

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.859 0.027 0.339 0.120
Pad 2 v Pad 3 0.007 < 0.00] < 0.001 0.003
Pad 1 v Pad 3 0.025 0.127 0.006 0.006

 

 

 

From Tables 31, 32 and 35 we observe that on average the apex location of Pads 1
and 2 are at nearly the same height above the seat pan at all recline angles, except for the
50‘h percentile anthropometric group at a 15° recline angle.

Comparisons between each anthropometric group with each lower back support
pad at all four recline angles were carried out and the statistical p-value results have been
provided in Tables 36 and 37. Table 36 provides data corresponding to the office seating
recline angles while Table 37 provides similar data corresponding to the vehicle seating

recline angles. The bolded p-values indicate significant differences.

76

Table 36: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex heights above seat pan for each anthropometric
group considered individually (office seating). Values in bold indicate significance.
MM = 50th percentile males (n=10), SF = 5th percentile females (n=4), LM = 95th
percentile males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.613 0.583 0.943 0.839 0.414 0.715
SF v LM 0.072 0.108 0.323 0.053 0.063 0.219
MM v LM 0.055 0.048 0.232 0.184 0.414 0.800

 

 

Table 37: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex heights above seat pan for each anthropometric
group considered individually (vehicle seating). Values in bold indicate significance.
MM = 50th percentile males (n=10), SF = 5t percentile females (n=4), LM = 95th
percentile males (n=4).

 

 

Anthropometric 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.841 0.568 0.514 0.860 0.943 0.403
SF v LM 0.080 0.089 0.434 0.074 0.152 0.085
MM v LM 0.032 0.082 0.723 0.224 0.127 0.377

 

 

There is only one case of significant result observed in each of the two Tables 36
and 37 indicating that in general, variation in subject anthropometry does not
significantly affect the position of the lower back support pads in terms of height above

the seat pan.

77

F ore-aft Prominence

Tables 38 and 39 provide fore-aft data of the apex of each pad with respect to the
seat back for all 18 subjects. Averages have been calculated for each anthropometric
group individually as well as for all subjects together. Table 38 lists data corresponding
to the two office seating recline angles of 100 and 150 while Table 39 lists similar data for
the vehicle seating recline angles of 200 and 24°. Positive values indicate apex
prominence in front of the plane of the seat back while negative values indicate position

of pad rearward of the seat back plane.

78

Table 38: F ore-aft prominences with respect to seat back of each pad for all 18
subjects in office seating. All values are in mm. Negative sign indicates the apex of
the pad was positioned rearward of the plane formed by the seat back frame.

 

Subject 10° 15°
[D Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
50th percentile males
P2A 4 7 2 14 5 4
P2B 24 24 18 30 25 15
P2C 17 15 11 17 1 1 14
P2D 10 6 13 9 4 5
P2E 3 -4 -4 1 -5 -7
P2F 5 -6 -6 1 -13 -12
PZG 15 8 5 6 9 9
PZH 3 -5 -5 6 -8 -5
P21 19 14 14 18 18 18
P21 13 11 8 1 1 12 3
Avg 11 7 6 11 6 4
5th percentile females
P2K 14 13 l 1 8 4 5
PZL 8 1 2 5 -3 -7
PZM 12 9 2 1 1 4 6
PZN 12 7 13 16 5 19
Avg 11 7 7 10 3 6
95th percentile males
P2U 10 14 9 9 9 1 1
P2V 16 19 18 16 17 19
P2W 12 10 12 9 8 10
P2X 16 15 13 9 1 0
Avg 13 14 13 10 8 10
Total 12 9 7 11 6 6
Avg
SD 6 8 7 7 9 9

 

 

 

79

Table 39: F ore-aft prominences with respect to seat back of each pad for all 18
subjects in vehicle seating. All values are in mm. Negative sign indicates the apex of
the pad was positioned rearward of the plane formed by the seat back frame.

 

 

Subject 20° 24°
ID Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
50th percentile males
P2A 2 3 5 3 6
P2B 19 4 26 28 22 23
P2C 16 6 -1 21 12 3
P2D 3 1 0 5 -1 -4
P2E -1 -10 -3 -4 -7 -6
P2F -2 -6 -10 —4 -3 —6
P2G 3 5 5 5 12 8
PZH 6 -10 —10 3 -8 -10
P21 11 13 6 10 8 12
PM 5 5 7 1 1 5 6
Avg 7 1 2 8 4 3
5th percentile females
9 5 -3 12 2 8
P2L 5 3 9 10 5 3
P2M 1 1 1 3 10 5 1
P2N 19 10 1 21 8 2
Avg 11 4 2 13 5 3
95th percentile males
1 5 8 5 8
P2V 17 15 15 18 18 22
P2W 4 1 5 7 6 4
P2X 11 3 4 15 16 3
Avg 10 5 7 12 11 9
Total 8 3 3 10 6 4
Avg
SD 6 7 8 8 8 8

 

 

80

Table 40 summarizes the results of the statistical tests performed on the data
presented in Tables 38 and 39. The bolded p-values indicate significant differences.
Table 40: Summary of p-values of statistical tests performed for the comparison of

lower back support pads' apex fore-aft position relative to plane of seat back. Values
in bold indicate significance.

 

 

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.009 < 0.001 < 0.001 0.012
Pad 2 v Pad 3 0.364 0.914 0.672 0.510
Pad 1 v Pad 3 < 0.001 0.002 0.011 < 0.001

 

From Table 40 we observe that Pad 1 has significantly different results when
compared to Pads 2 and 3. Tables 38 and 39 indicate that the preferred apex position of
Pad 1 is at a greater distance in front of the seat back plane as compared to the preferred
positions of Pads 2 and 3.

Statistical p-values computed by comparing each anthropometric group at all
recline angles with each lower back support pad have been provided in Tables 41 and 42.
Table 41 provides data corresponding to the office seating recline angles while Table 42
provides similar data corresponding to the vehicle seating recline angles. The bolded p-

values indicate significant differences.

81

Table 41: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex fore-aft prominence positions relative to the plane of
the seat back for each anthropometric group considered individually (office
seating). Values in bold indicate significance. MM = 50th percentile males (n=10), SF
= 5th percentile females (n=4), LM = 95'" percentile males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 1.000 0.925 0.772 0.789 0.602 0.826
SF v LM 0.346 0.065 0.134 0.686 0.148 0.543
MM v LM 0.586 0.168 0.129 0.908 0.651 0.339

 

 

Table 42: Summary of p-values of statistical tests performed for the comparison of
lower back support pads' apex fore-aft prominence positions relative to the plane of
the seat back for each anthropometric group considered individually (vehicle
seating). Values in bold indicate significance. MM = 50th percentile males (n=10), SF
= 5th percentile females (n=4), LM = 95th percentile males (n=4).

 

Anthropometric 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.283 0.366 0.971 0.351 0.887 0.953
SF v LM 0.812 0.951 0.235 0.750 0.200 0.263
MM v LM 0.396 0.372 0.385 0.475 0.210 0.314

 

 

 

Results from Tables 41 and 42 show no significant differences indicating that
variation in subject anthropometry does not significantly affect the position of the lower
back support pads in terms of fore-aft prominence with respect to the plane of the seat

back.

82

Forces
Reference File

Table 43 presents the force reference file data for the upright seat back position
(0° with respect to vertical) and then individually for each of the three lower back support
pads. These data represent the measurement when no load was placed on the force
transducers. Thus, these data were rotated to the correct recline angle and subtracted from

each file.

Table 43: Reference file force data values. Negative sign indicates direction of
force: inferiorly for F x, left lateral for Fy and normal into the pad for F2.

 

Upright Lower Back Thoracic
Fx Fy Fz Fx Fy F7.
Pad 1 —0.3 -3.0 -6.0 -0.9 -1.7 -4.7
Pad 2 2.9 —3.1 -6.0 -0.9 -1.7 -4.6
Pad 3 1.9 ~3.1 -6.1 —0.9 -1.7 -4.6
Pad 1 Lower Back Thoracic
Fx' Fy' Fz' Fx' Fy' Fz'
10° 0.7 -3.0 -6.0 0.0 -1.7 4.8
15° 1.3 —3.0 -5.9 0.4 -1.7 -4.8
20° 1.8 -3.0 -5.8 0.8 -1.7 -4.7
24° 2.2 -3.0 -5.6 1.1 -1.7 -4.7
Pad 2 Lower Back Thoracic
Fx' Fy' Fz' Fx‘ Fy' Fz'
10° 3.9 -3.1 -5.4 -0.1 -1.7 —4.7
15° 4.4 -3.1 -5.0 0.3 —1.7 -4.7
20° 4.8 -3.1 -4.6 0.7 -l.7 -4.7
24° 5.1 -3.1 -4.2 1.0 -l.7 -4.6
Pad 3 Lower Back Thoracic
Fx' Fy' Fz' Fx' Fy' Fz'
10° 2.9 -3.1 —5.6 -0.1 -1.7 -4.7
15° 3.4 —3.1 -5.4 0.3 -1.7 -4.7
20° 3.8 -3.1 -5.1 0.7 -1.7 -4.6
24° 4.2 -3.1 -4.8 1.1 -1.7 —4.6

 

 

 

83

Normal Forces

Tables 44 and 45 provide the numerical normal force (F Z) data values exerted on
the thorax support in the office and vehicle seating recline angles respectively. Tables 46
and 47 present similar data corresponding to the lower back support pads.

Results from these 4 Tables 44, 45, 46 and 47 indicate greater forces being
excited on both the thoracic and lower back supports in the vehicle seating environment
as compared to the office seating. This indicates a correlation between recline angles and

support forces.

84

Table 44: Normal forces (F l) exerted on the thorax support at 10° and 15° recline
angles (office seating). All forces are in Newtons. Negative sign indicates direction of
force — into the thorax support for normal forces. SD = Standard Deviation.

 

Subject ID 10° recline 15° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -48.9 -51.2 -57.5 -80.4 -65.0 -61.1
P2B —46.7 -52.0 -38.5 -70.2 -70.0 -63.8
P2C -54.2 -67.1 -53.3 -60.9 -60.7 -62.9
P2D -62.8 -55.5 -50.5 -61.7 -64.9 -52.9
P2E —51.8 44.9 -46.8 -66.1 -63.0 -60.7
P217 495 —48.7 -62.7 -61.7 -61.9 -64.8
P2G -53.3 -52.4 -51.6 -74.5 —69.8 -67.5
P2H -58.9 -62.7 -62.0 -79.1 -71.2 836
P2] -67.9 -61.6 -40.9 -73.7 -86.4 -72.8
P2J —40.1 —48.7 -48.3 -41.9 -47.6 -42.9
Avg -53.4 -54.5 -51.2 -67.0 -66.1 -63.3
SD 8.1 7.1 8.1 11.3 9.8 10.8
5th percentile
females
P2K -38.6 -37.1 -38.0 —49.4 -42.3 -40.5
P2L —40.1 —44.6 -27.3 -52.6 -59.8 -52.2
P2M -26.5 -31.1 -32.5 —38.1 -41.6 -43.2
P2N -66.5 -61.4 -37.4 -63.1 -58.5 -45.7
Avg -42.9 -43.5 -33.8 -50.8 -50.5 -45.4
SD 16.8 13.1 5.0 10.3 9.9 5.0
95th percentile
males
P2U -90.6 -88.1 -76.2 —105.0 -95.9 —82.1
P2V -78.4 -91.5 -84.7 -113.5 -117.6 -103.8
P2W -56.2 -55.6 -65.4 —78.3 -65.5 -57.1
P2X -53.2 -46.5 -50.5 -53.2 -69.8 -48.1
Avg -69.6 -70.4 -69.2 -87.5 -87 .2 -72.8
SD 17.9 22.7 14.8 27.4 24.3 25.2
Total Avg -54.7 -55.6 -51.3 -68.0 -67.3 -61.4
SD 15.1 15.3 15.0 19.5 18.3 16.5

 

85

Table 45: Normal forces (Fl) exerted on the thorax support at 20° and 24° recline
angles (office seating). All forces are in Newtons. Negative sign indicates direction of
force — into the thorax support for normal forces. SD = Standard Deviation.

 

Subject ID 20° recline 24° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -117.8 -117.5 -104.7 ~118.3 -121.9 -100.2
PZB -127.2 -126.7 -128.9 -142.1 —144.3 -134.9
P2C -98.0 -107.3 -94.6 -121.7 -118.9 -109.3
P2D —117.7 -117.5 —92.3 -136.0 -123.5 -107.6
P2E —100.7 -109.2 -110.8 -115.6 -124.0 -120.3
PZF -163.9 -143.8 -151.4 -158.4 -161.4 -154.1
P2G -121.3 -125.5 -117.5 -137.0 -126.9 -127.1
PZH -106.0 -104.8 -99.2 -124.1 —123.6 —123.4
P21 -107.5 -119.1 -113.1 -131.8 -138.0 —121.6
P2J -96.8 -114.2 -105.4 —102.2 -122.8 -103.8
Avg -115.7 -118.6 -111.8 -128.7 -l30.5 -120.2
SD 19.9 11.4 17.7 15.8 13.4 16.2
5th percentile
females
P2K -67.0 -71.1 -55.5 -80.4 -80.4 ~78.2
P2L -72.2 -78.5 -79.5 -80.8 -83.9 -81.8
P2M -77.0 -65.2 -72.8 -76.2 -66.9 -65.4
P2N -98.2 -100.3 -86.3 -88.7 —106.2 -81.2
Avg -78.6 -78.8 -73.5 -81.5 -84.3 -76.7
SD 13.7 15.3 13.2 5.2 16.3 7.7
95th percentile
males
P2U -175.0 -213.7 -211.1 —219.6 -236.0 -192.4
P2V -209.3 -209.2 -204.2 ~232.1 -230.4 -196.9
P2W -133.9 -140.8 -130.3 -128.3 -146.9 -144.7
P2X -121.7 -121.1 -123.4 -115.3 -131.0 -137.6
Avg -160.0 -171.2 -167.2 -173.8 -186.1 -167.9
SD 40.0 47.2 46.8 60.5 54.9 31.1
Total Avg -117.3 -121.4 -115.6 -128.2 -132.6 -121.2
SD 36.1 39.0 40.4 42.2 43.5 36.1

 

86

Table 46: Normal forces (Fl) exerted on each lower back support pad at 10° and 15°
recline angles (office seating). All forces are in N ewtons. Negative sign indicates
direction of force — into the pad for normal forces. SD = Standard Deviation.

 

Subject ID 10° recline 15° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

501h percentile

 

 

males
P2A -66.3 68.9 -70.3 -64.2 -74.3 -81.0
P28 -69.8 -46.2 -80.5 -69.5 -57.0 —63. 1
P2C -50.1 -31.3 -42.3 —39.1 -41.5 —51.5
P2D -49.6 -38.3 -58.1 -52.3 -40.4 -61.5
P2E -49.4 -34.9 -40.2 -43.0 —35.2 -36.3
P2F -31.8 -16.0 -l4.5 -40.7 -14.9 -18.5
P2G -48.4 -33.3 —40.1 -30.7 -29.4 -31.9
P2H -77.7 -54.2 -52.5 —68.1 -65.4 -49.9
P21 -91.7 -89.3 -94.4 —81.2 -81.6 -82.3
P2] -53.1 -37.3 -40.8 -56.7 -33.3 -56.0
Avg -58.8 -45.0 -53.4 -54.6 -47 .3 -53.2
SD 17.4 21.1 23.3 16.2 21.4 20.4
5th percentile
females
P2K -33.9 -32.2 -36.4 -34.6 -37.9 -43.8
P2L —45.8 -36.7 -44.4 -42.3 -26.6 -25.6
P2M -48.5 -32.3 -34.3 -47.6 -31.5 -40.8
P2N -56.6 -52.7 -53.7 -57.6 -68.2 -71.8
Avg -46.2 -38.5 -42.2 -45.5 -4l.0 -45.5
SD 9.4 9.7 8.8 9.7 18.7 19.3
95th percentile
males
P2U -58.3 62.4 -70.5 -56.0 -73.0 -94.2
P2V -75.1 -79.3 -98.2 -80.2 -74.0 -1 18.1
P2W -48.9 -44.4 —46.2 -65.6 -47.0 -56.2
P2X -96.2 -66.7 —101.5 -112.6 -59.4 -114.9
Avg -69.6 -63.2 -79.1 -78.6 -63.4 -95.8
SD 20.8 14.4 26.0 24.8 12.8 28.5
Total Avg -58.4 -47.6 -56.6 -57.9 -49.5 -61.0
SD 17.8 19.2 24.4 20.2 20.0 28.4

 

87

Table 47: Normal forces (Fz) exerted on each lower back support pad at 20° and 24°
recline angles (vehicle seating). All forces are in Newtons. Negative sign indicates
direction of force — into the pad for normal forces. SD = Standard Deviation.

 

Subject ID 20° recline 24° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -120.7 -118.5 -152.4 -131.3 -124.7 -162.1
P2B -113.8 -114.6 -104.1 -120.7 -96.6 -110.1
P2C -75.2 -56.0 -79.3 -69.5 —62.7 -72.0
P2D -79.4 -64.1 -101.9 -71.3 -70.6 -96.3
PZE -74.4 —49.5 -57.7 -57.3 —42.2 —60.1
P2F -34.2 -56.5 -51.7 -60.9 —57.3 -72.1
P2G —46.0 -42.5 -56.5 —45.4 —58.1 -58.2
P2H -140.6 -120.8 -124.1 -131.9 -126.2 -114.6
P21 -151.4 -122.7 -129.5 -128.3 -132.1 -145.0
PZJ -109.9 -72.2 -85.9 -110.3 —65.5 -94.6
Avg -94.5 -8l.7 -94.3 -92.7 -83.6 -98.5
SD 39.0 33.2 34.2 34.8 33.4 35.1
5th percentile
females
P2K -59.3 -52.1 -74.2 -52.1 -54.5 -60.4
P2L —73.6 -58.4 -50.6 -71.1 -58.7 -57.4
PZM -74.9 -61.3 -57.9 -69.9 69.8 —72.5
P2N -81.0 -61.9 -70.9 -74.3 -71.6 88.4
Avg -72.2 -58.4 -63.4 -66.8 -63.6 -69.7
SD 9.2 4.5 11.1 10.0 8.4 14.1
95th percentile
males
P2U -116.5 -79.5 -93.6 —109.1 -74.2 —171.3
P2V -170.7 -158.5 -190.1 -152.2 -152.3 -l98.8
P2W -100.8 -92.7 -93.7 -130.3 -89.2 -97.3
P2X -169.6 -146.6 -170.5 -181.3 -154.9 -169.3
Avg -139.4 ~119.3 -137.0 -143.2 -117.7 -159.2
SD 36.1 39.0 50.6 30.9 42.0 43.4
Total Avg -99.5 -84.9 -96.9 -98.2 -86.7 -105.6
SD 40.2 36.1 41.7 39.4 35.6 45.0

 

88

Tables 48 and 49 provide the normal forces exerted on the thorax support
expressed in terms of percentage of Body Weight (BW) for all subjects. Table 48
provides data corresponding to the office seating recline angles while Table 49 provides
similar data corresponding to the vehicle seating recline angles.

Likewise, Tables 50 and 51 provide the normal forces exerted on the lower back
support pads expressed in terms of percentage of Body Weight (BW) for all subjects.
Table 50 provides data corresponding to the office seating recline angles while Table 51
provides similar data corresponding to the vehicle seating recline angles.

In all four Tables 48, 49, 50 and 51, a narrow percentage range was observed
although numerical percentage values are greater for the vehicle seating as compared to

the office seating.

89

Table 48: Normal forces (Fl) exerted on thorax support expressed in terms of
percentage of Body Weight (BW) for office seating recline angles. Body Weight is in
Newtons. All other values are in percentage. SD = Standard Deviation.

 

 

Subject Body 10° 15°
ID Weight Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
(BW)
50th
percentile
males
P2A 790 6 6 7 10 8 8
P28 735 6 7 5 10 10 9
P2C 597 9 11 9 10 10 l 1
P2D 724 9 8 7 9 9 7
P2E 555 9 8 8 12 11 1 1
PZF 708 7 7 9 9 9 9
P2G 608 9 9 8 17 1 1 11
PZH 730 8 9 8 1 1 10 1 1
P21 750 9 8 5 10 12 10
P2J 657 6 7 7 6 7 7
Avg 686 8 8 8 10 10 9
SD 77 l 1 1 2 1 2
5th
percentile
females
P2K 391 10 9 10 13 1 1 10
P2L 488 8 9 6 1 1 12 1 1
P2M 457 6 7 7 8 9
P2N 608 1 1 10 6 10 10 8
Avg 486 9 9 7 11 10 10
SD 91 2 1 2 2 1 1
95th
percentile
males
P2U 1 123 8 8 7 9 9 7
P2V 1332 6 7 6 9 9 8
P2W 719 8 8 9 1 1 9 8
P2X 808 7 6 6 7 9 6
Avg 996 7 7 7 9 9 7
SD 283 1 1 1 2 0 1

 

 

90

Table 49: Normal forces (Fl) exerted on thorax support expressed in terms of
percentage of Body Weight (BW) for vehicle seating recline angles. Body Weight is
in Newtons. All other values are in percentage. SD = Standard Deviation.

 

 

Subject Body 20° 24°
ID Weight Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
(BW)
50th
percentile
males
P2A 790 15 15 13 15 15 13
P28 735 17 17 18 19 20 18
P2C 597 16 18 16 20 20 18
P2D 724 16 16 13 19 17 15
PZE 555 18 20 20 21 22 22
P2F 708 23 20 21 22 23 22
P2G 608 20 21 19 23 21 21
P2H 730 15 14 14 17 17 17
P21 750 14 16 15 18 18 16
P2J 657 15 17 16 16 19 16
Avg 686 17 17 16 19 19 18
SD 77 3 2 3 3 2 3
5th
percentile
females
P2K 391 17 18 14 21 21 20
P2L 488 15 16 16 17 17 17
P2M 457 17 14 16 17 15 14
P2N 608 16 16 14 15 17 13
Avg 486 16 16 15 17 17 16
SD 91 l 2 1 3 2 3
95th
percentile
males
P2U 1123 16 19 19 20 21 17
P2V 1332 16 16 15 17 17 15
P2W 719 19 20 18 18 20 20
P2X 808 15 15 15 14 16 17
Avg 996 16 17 17 17 19 17
SD 283 2 2 2 2 2 2

 

 

91

Table 50: Normal forces (F2) exerted on lower back support expressed in terms of
percentage of Body Weight (BW) for office seating recline angles. Body Weight is in
Newtons. All other values are in percentage. SD = Standard Deviation.

 

 

Subject Body 10° 15°
ID Weight Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
(BW)
50th
percentile
males
P2A 790 8 9 9 8 9 10
P28 735 10 6 1 l 9 8 9
P2C 597 8 5 7 7 7 9
P2D 724 7 5 8 7 6 8
P2E 555 9 6 7 8 6 7
PZF 708 4 2 2 6 2 3
P2G 608 8 5 7 5 5 5
P21] 730 1 1 7 7 9 9 7
P21 750 12 12 13 1 1 1 1 1 1
P2J 657 8 6 6 9 5 9
Avg 686 9 6 8 8 7 8
SD 77 2 3 3 2 3 2
5th
percentile
females
P2K 391 9 8 9 9 10 11
P2L 488 9 8 9 9 5 5
P2M 457 l 1 7 7 10 7 9
P2N 608 9 9 9 9 11 12
Avg 486 9 8 9 9 8 9
SD 91 1 1 1 1 3 3
95th
percentile
males
P2U 1123 5 6 6 5 7 8
P2V 1332 6 6 7 6 6 9
P2W 719 7 6 6 9 7 8
P2X 808 12 8 13 14 7 14
Avg 996 7 6 8 9 6 10
SD 283 3 1 4 1 3

 

 

92

Table 51: Normal forces (Fl) exerted on lower back support expressed in terms of
percentage of Body Weight (BW) for vehicle seating recline angles. Body Weight is
in Newtons. All other values are in percentage. SD = Standard Deviation.

 

 

Subject Body 20° 24°
Weight Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
(BW)
50th
percentile
males
P2A 790 15 15 19 17 16 21
P28 735 15 16 14 16 13 15
P2C 597 13 9 13 12 10 12
P2D 724 11 9 14 10 10 13
P2E 555 13 9 10 10 8 11
PZF 708 5 8 7 9 8 10
P2G 608 8 7 9 7 10 10
P21-l 730 19 17 17 18 17 16
P21 750 20 16 17 17 18 19
P2J 657 17 11 13 17 10 14
Avg 686 14 12 14 13 12 14
SD 77 5 4 4 4 4 4
5th
percentile
females
P2K 391 15 13 19 13 14 15
P2L 488 15 12 10 15 12 12
P2M 457 16 13 13 15 15 16
P2N 608 13 10 12 12 12 15
Avg 486 15 12 13 l4 13 14
SD 91 1 2 4 l 2 2
95th
percentile
males
P2U 1 123 10 7 8 10 7 15
P2V 1332 13 12 14 11 11 15
P2W 719 14 13 13 18 12 14
P2X 808 21 18 21 22 19 21
Avg 996 15 13 14 15 12 16
SD 283 5 5 5 6 5 3

 

 

93

Table 52 summarizes the results of the statistical tests performed for the
comparison of normal forces exerted on the thorax support under the effect of each lower
back support pad taking all subjects into consideration (n=18). The bolded p-values

indicate significant differences.

Table 52: Summary of p-values of statistical tests performed for the comparison of
normal forces exerted on thorax support at all 4 recline angles. Values in bold
indicate significance (n = 18).

 

 

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.555 0.941 0.167 0.325
Pad 2 v Pad 3 0.107 0.016 0.311 0.002
Pad 1 v Pad 3 0.258 0.007 0.592 0.061

 

Table 53 summarizes the results of the statistical tests performed for the
comparison of normal forces exerted on each of the lower back support pad under all
conditions of recline for all subjects together (n=18). The bolded p-values indicate

significant differences.

Table 53: Summary of p-values of statistical tests performed for the comparison of
normal forces exerted on each lower back support pad at all 4 recline angles. Values
in bold indicate significance (n = 18).

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 < 0.001 0.095 0.002 0.085
Pad 2 v Pad 3 0.004 0.016 0.002 < 0.001
Pad 1 v Pad 3 0.770 0.718 0.547 0.203

 

 

 

94

From Tables 46, 47 and 53, we observe that normal force values exerted upon Pad
2 are significantly lower than those exerted on Pad 3 under all conditions of recline.
However, when comparing Pad 2 with Pad 1, this observation holds true only at two out
of the four recline angles tested. There is no significant difference in normal force values
exerted on Pads 1 and 3 under all conditions of recline.

Tables 54 and 55 provide a summary of the statistical p-values computed from the
comparisons made between each anthropometric group for normal forces exerted on
thorax support. Each lower back support pad has been considered at all four recline
angles. Table 54 provides data corresponding to the office seating recline angles while

Table 55 provides similar data corresponding to the vehicle seating recline angles.

95

Table 54: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on thorax support, each anthropometric being
considered individually (office seating). Values in bold indicate significance. MM =
50th percentile males (n=10), SF = 5th percentile females (n=4), LM = 95th percentile
males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.132 0.063 0.002 0.030 0.021 0.009
SF v LM 0.073 0.086 0.004 0.046 0.032 0.057
MM v LM 0.104 0.288 0.011 0.229 0.089 0.832

 

 

Table 55: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on thorax support, each anthropometric being
considered individually (vehicle seating). Values in bold indicate significance. MM =
50th percentile males (n=10), SF = 5th percentile females (n=4), LM = 95th percentile
males (n=4).

 

 

 

Anthropometric 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.005 < 0.001 0.002 < 0.001 0.006 < 0.001
SF v LM 0.008 0.029 0.029 0.029 0.029 0.029
MM v LM 0.015 0.028 0.020 0.029 0.028 0.013

 

96

Similarly, Tables 56 and 57 provide a summary of the statistical p-values
computed from the comparisons made between each anthropometric group for normal
forces exerted on each lower back support pad. Comparisons have been made at all four
recline angles. Table 56 provides data corresponding to the office seating recline angles
while Table 57 provides similar data corresponding to the vehicle seating.

Although there are a few cases of significant results, there is no statistical trend

observed in either of the two Tables 56 and 57.

97

Table 56: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on lower back support pads, each anthropometric being
considered individually (office seating). Values in bold indicate significance. MM =
50th percentile males (n=10), SF = 5th percentile females (n=4), LM = 95th percentile
males (n=4).

 

 

Anthropometric 10° 15°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.203 0.572 0.378 0.323 0.620 0.530
SF v LM 0.086 0.030 0.036 0.047 0.096 0.026
MM v LM 0.337 0.142 0.095 0.057 0.192 0.008

 

 

Table 57: Summary of p-values of statistical tests performed for the comparison of
normal force values exerted on lower back support pads, each anthropometric being
considered individually (vehicle seating). Values in bold indicate significance. MM =

50th percentile males (n=10), SF = 5‘" percentile females (n=4), LM = 95th percentile

males (n=4).

 

 

Anthropometric 20° 24°
groups Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3
MM v SF 0.289 0.437 0.109 0.437 0.270 0.145
SF v LM 0.029 0.029 0.029 0.030 0.029 0.008
MM v LM 0.071 0.092 0.089 0.057 0.133 0.018

 

98

 

Tables 58 and 59 provide the pressure values exerted on each pad for all the three
anthropometric groups individually. Table 58 lists data corresponding to the office
seating recline angles while Table 59 provides similar data corresponding to the vehicle

seating recline angles.

99

Table 58: Average pressure values exerted on each Pad by each anthropometric
group for office seating. 50th M = 50th percentile males, 5th F = 5th percentile females,
95th M = 95th percentile males.

 

 

Recline Anthropometric Force Pad Surface Pressure

Angle Group (N) Area (m2) (N/mz)

Pad 1
10° 50‘“ M -58.8 0.035 4679.6
10° 5‘“ F -46.2 0.035 4319.8
10° 95‘“ M -69.6 0.035 4988.3
15° 50‘“ M -54.6 0.035 4559.4
15° 5'“ F 45.5 0.035 4300.4
15° 95‘“ M -78.6 0.035 -2246.0
Avg Pressure = -1682.3

Pad 2
10° 50‘“ M -450 0.029 4 550.6
10° 5‘“ F -38.5 0.029 4326.6
10° 95‘“ M -63.2 0.029 -2178.6
15° 50‘“ M -473 0.029 4630.8
15° 5‘“ F 41.0 0.029 4415.4
15° 95‘“ M -63.4 0.029 -2185.2
Avg Pressure = -l714.6

Pad 3
10° 50'“ M 53.4 0.036 4482.2
10° 5““ F -422 0.036 4172.0
10° 95‘“ M -791 0.036 -2196.6
15° 50‘“ M -532 0.036 4477.8
15° 5““ F -455 0.036 4263.5
150 95‘“ M -95.8 0.036 -2662.2
Avg Pressure = -1709.0

 

100

 

Table 59: Average pressure values exerted on each Pad by each anthropometric
group for vehicle seating. 50th M = 50th percentile males, 5th F = 5th percentile
females, 95th M = 95t percentile males.

 

 

Recline Anthropometric Force Pad Surface Pressure
Angle Group (N) Area (m2) (N/mz)
Pad 1
20° 50‘“ M -945 0.035 -27014
20° 5‘“ F -722 0.035 -2062.4
20° 95'“ M 439.4 0.035 -3983.1
24° 50““ M -927 0.035 -2648.1
24° 5‘“ F -66.8 0.035 4909.2
24° 95‘“ M 443.2 0.035 4092.4
Avg Pressure = -2899.4
Pad 2
20° 50““ M -81.7 0.029 -2818.6
20° 5‘“ F -58.4 0.029 20147
20° 95'“ M 4 19.3 0.029 4114.4
24° 50‘“ M -83.6 0.029 -2882.9
24° 5‘“ F -63.6 0.029 -21945
24° 95‘“ M 4 17.7 0.029 4057.1
Avg Pressure = -3013.7
Pad 3
20° 50‘“ M -943 0.036 -2619.2
20° 5‘“ F -63.4 0.036 -176l.2
20° 95‘“ M 437.0 0.036 -3804.4
24° 50‘“ M -98.5 0.036 -2736.4
24° 5‘“ F -69.7 0.036 4935.3
24° 95““ M 4 59.2 0.036 4421.0
AgPressure = -2879.6

 

101

 

Vertical Shear Forces
Tables 60 and 61 provide the numerical vertical shear force (F x) data values
exerted on the thorax support in the office and vehicle seating recline angles respectively.

Tables 62 and 63 present similar data corresponding to the lower back support pads.

102

Table 60: Vertical shear forces (Fx) exerted on the thorax support at 10° and 15°
recline angles (office seating). All forces are in Newtons. The negative sign indicates
an inferiorly directed force — inferiorly for Vertical Shear forces. SD = Standard
Deviation.

 

Subject ID 10° recline 15° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -7.2 -2.9 -3.2 2.6 2.0 0.3
PZB -18.0 ~15.5 -11.4 —11.1 -13.1 -5.5
P2C -6.0 -8.9 -8.9 -10.6 -13.4 -14.8
P2D -8.0 -7.4 -9.5 -7.9 -8.3 -5.4
P2E -4.3 —1.6 -4.7 -2.6 -5.3 -1.9
P2F -l8.7 -17.3 -16.8 -15.7 -11.5 -18.2
PZG —10.0 -8.8 -7.3 -8.6 —4.9 —5.4
P2H -10.5 -4.1 -7.7 —13.7 -2.5 -5.0
P21 -13.6 -l3.2 -6.5 -3.3 -13.7 -15.4
P2J -11.2 -9.4 -10.1 -7.9 -11.5 49
Avg -10.7 -8.9 -8.6 -7.9 -8.2 -7.6
SD 4.8 5.2 3.8 5.5 5.4 6.2
5th percentile
females
P2K -4.2 -4.4 -3.8 —4.1 -1.1 -2.3
P2L —7.6 -8.8 -2.9 —14.9 -6.3 -1.0
P2M -9.4 -5.8 -6.0 -7.3 -8.6 -6.4
P2N 0.3 1.6 1.2 -1.2 0.6 09
Avg -5.2 -4.3 -2.9 -6.9 -3.9 -2.7
SD 4.2 4.4 3.0 5.9 4.3 2.6
95th percentile
males
P2U -36.7 -38.6 -27.6 -37.9 ~28.3 -25.7
P2V -25.2 -18.1 -19.1 —34.9 -14.9 -30.5
P2W -33.8 -24.6 -28.4 -36.3 -31.6 -25.6
P2X -19.2 -23.1 -15.1 -11.2 -22.8 -10.4
Avg -28.7 -26.1 -22.6 -30.1 -24.4 -23.0
SD 8.0 8.8 6.5 12.7 7.3 8.8
Total Avg -13.5 -11.7 -10.4 -12.6 -10.8 -9.9
SD 10.1 9.9 8.2 12.0 9.3 9.5

 

103

Table 61: Vertical shear forces (F x) exerted on the thorax support at 20° and 24°
recline angles (vehicle seating). All forces are in Newtons. The negative sign
indicates an inferiorly directed force — inferiorly for Vertical Shear forces. SD =
Standard Deviation.

 

Subject ID 20° recline 24° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -12.5 -7.1 -5.9 —5.5 -4.0 -3.6
P2B -19.9 -22.3 -21.7 -21.8 -2.8 -18.2
P2C -18.1 -18.5 -10.6 -2l.2 -17.4 -7.7
P2D -26.9 —23.3 -17.4 -18.7 -25.5 -16.6
P2E -16.2 —4.7 -11.8 -13.5 -3.6 -5.5
P2F -43.0 -31.8 —32.4 —3 1.2 -30.4 -36.4
P2G -13.0 -16.2 -9.2 -17.9 -14.4 -13.7
P2H -9.1 1.7 4.0 -17.7 -0.9 -5.1
P2] -40.8 -30.1 -26.1 —24.4 —39.6 -25.3
PM -27.7 —26.1 -19.8 -24.2 -24.1 —19.4
Avg -22.7 -17.9 -15.1 -19.6 -16.3 -15.2
SD 11.7 11.2 10.6 6.9 13.4 10.4
5th percentile
females
P2K -11.3 —4.7 -6.8 -8.3 -l .1 -6.5
P2L -20.3 -20.8 -l3.4 -20.3 -15.3 -13.4
PZM -15.0 -10.6 -11.6 -10.6 -11.6 -7.3
P2N -1.5 -7.0 7.0 -1.8 1.9 4.6
Avg -12.0 -10.8 -6.2 -10.2 -6.5 -5.7
SD 7.9 7.1 9.2 7.7 8.2 7.5
95th percentile
males
P2U -21.7 -34.8 -62.5 -34.2 -51.2 -61.8
P2V -55.4 -90.6 -111.7 -81.4 -105.9 -137.8
P2W -51.7 —53.9 —50.6 -56.0 -69.2 -55.2
P2X -41.7 -54.9 -37.9 -38.2 -58.7 -46.9
Avg -42.6 -58.6 -65.6 -52.5 -71.3 -75.4
SD 15.1 23.3 32.3 21.5 24.2 42.0
Total Avg -24.8 -25.3 -24.3 -24.8 -26.3 -26.4
SD 15.5 22.7 28.1 19.1 28.9 33.5

 

104

Table 62: Vertical shear forces (F ") exerted on lower back support pads at 10° and
15° recline angles (office seating). All forces are in Newtons. The negative sign
indicates an inferiorly directed force — inferiorly for Vertical Shear forces. SD =
Standard Deviation.

 

Subject ID 10° recline 15o recline
Pad 1 Pad 2 Pad 3 Pad ] Pad 2 Pad 3

 

 

50th percentile
males
P2A -19.7 -21.4 -18.5 -23.1 -19.4 -21.0
PZB -12.3 -21.8 -27.6 -20.1 -15.5 -15.9
PZC -18.7 -15.2 -14.7 —15.5 -16.8 -15.5
P2D -12.4 -15.9 -14.2 -13.2 -17.5 -16.9
P2E —14.7 —11.1 -10.8 -14.0 -9.3 —12.6
P2F -12.5 —8.0 —5.9 -10.8 -7.1 -7.5
PZG -10.9 -11.1 -14.0 -6.8 -11.7 —12.7
P2H -23.9 -17.6 -15.6 -26.1 -18.5 -18.8
P21 -23.9 -16.9 -25.6 -28.3 -29.9 -13.6
PZJ —14.2 -15.9 -11.4 -14.9 -7.3 -17.1
Avg -16.3 -15.5 -15.8 -l7.3 -15.3 -15.2
SD 4.9 4.4 6.6 6.9 6.9 3.8
5th percentile
females
P2K -6.6 -5.1 -7.8 -6.9 -5.9 -7.0
P2L -3.5 -3.9 -4.5 -2.6 -0.3 -1.6
P2M -4.4 -5.9 -6.2 -6.1 4.0 -1.6
PZN -24.4 -17.6 -14.5 -25.0 -22.9 -24.3
Avg -9.7 -8.1 -8.2 -10.1 -6.3 -8.6
SD 9.8 6.4 4.4 10.1 11.8 10.7
95th percentile
males
P2U -14.5 -8.8 ~2.1 -12.6 —5.6 -18.4
P2V 0.4 -8.0 -6.1 -16.4 -16.2 4.6
P2W —6.8 -5.5 -8.1 -8.1 -5.1 -7.6
P2X 1.] -0.2 -5.1 2.0 2.4 -5.3
Avg -4.9 -5.6 -5.3 -8.8 -6.1 -6.7
SD 7.3 3.9 2.5 7.9 7.7 9.4
Total Avg -12.3 -11.7 -11.8 -13.8 -11.2 -11.8
SD 7.9 6.4 7.1 8.4 9.0 7.7

 

105

Table 63: Vertical shear forces (F x) exerted on lower back support pads at 20° and
24° recline angles (vehicle seating). All forces are in Newtons. The negative sign
indicates an inferiorly directed force — inferiorly for Vertical Shear forces. SD =

Standard Deviation.

 

Subject 1D 20° recline 24° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -22.5 -16.0 -25.0 -15.2 -17.0 -26.4
PZB —18.4 -29.7 -36.9 -27.0 -28.4 -27.0
PZC -19.9 -17.1 -15.9 -25.4 -23.0 -18.5
P20 -11.7 -24.5 -21.3 —11.6 -7.1 -12.5
P2E -9.2 —9.5 -l4.7 —6.8 -8.4 -12.2
P2F -6.8 -8.8 ~13.7 -4.7 -9.8 ~10.2
P2G —10.5 -13.5 ~15.0 -11.5 -11.2 -9.1
P2H -32.1 -20.9 -21.7 -29.6 -19.0 -20.1
P21 -14.1 -18.7 -19.9 -16.6 -2.5 -27.8
P2J -7.5 -8.4 -20.1 ~14.9 -9.8 —30.2
Avg -15.3 -16.7 -20.4 -l6.3 -l3.6 -l9.4
SD 8.0 7.0 6.9 8.5 8.0 8.1
5th percentile
females
P2K -6.5 -7.0 -4.8 -8.5 -5.4 —9.9
P2L -1.5 4.6 -4.4 11.3 3.2 -7.0
P2M -3.6 2.4 -2.4 -2.4 0.8 1.0
P2N -17.8 -9.3 -7.7 -18.3 —11.7 —16.7
Avg -7.3 -2.3 -4.8 -4.4 -3.3 -8.2
SD 7.3 6.9 2.2 12.4 6.7 7.3
95th percentile
males
P2U -54.0 -5.2 -13.2 -12.9 5.6 -24.5
P2V -23.3 -23.0 -20.9 —27.7 —17.3 -30.1
P2W -5.9 -6.2 -13.1 -6.0 —4.5 -6.0
P2X 11.6 24.7 -28.9 13.4 18.3 2.2
Avg -17.9 -2.4 -19.0 -8.3 0.5 -14.6
SD 28.0 19.9 7.5 17.0 15.1 15.2
Total Avg -14.1 -10.3 ~16.6 -11.9 -8.2 -15.8
SD 14.0 12.6 8.8 12.0 11.1 10.3

 

106

Table 64 summarizes the results of the statistical tests performed for the
comparison of vertical shear forces exerted on the thorax support under all conditions of

recline for all subjects (n=18). The bolded p-values indicate significant differences.

Table 64: Summary of p-values of statistical tests performed for the comparison of
vertical shear forces exerted on thorax support at all 4 recline angles. Values in bold
indicate significance (n = 18).

 

 

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.103 0.343 0.841 0.614
Pad 2 v Pad 3 0.302 0.543 0.212 0.968
Pad 1 v Pad 3 0.003 0.090 0.034 0.304

 

Likewise, Table 65 summarizes the results of the statistical tests performed for the
comparison of vertical shear forces exerted on each lower back support pad under all
conditions of recline for all subjects (n=18). The bolded p-values indicate significant

differences.

Table 65: Summary of p-values of statistical tests performed for the comparison of
vertical shear forces exerted on each lower back support pad at all 4 recline angles.
Values in bold indicate significance (n = 18).

 

 

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.563 0.017 0.243 0.145
Pad 2 v Pad 3 0.867 0.099 0.012 0.001
Pad 1 v Pad 3 0.746 0.247 0.501 0.120

 

107

Lateral Shear Forces
Tables 66 and 67 provide the numerical lateral shear force (F y) data values exerted
on the thorax support in the office and vehicle seating recline angles respectively. Tables

68 and 69 present similar data corresponding to the lower back support pads.

108

Table 66: Lateral shear forces (Fy) exerted on the thorax support at 10° and 15°
recline angles (office seating). All forces are in Newtons. A negative sign indicates
that the force is directed laterally toward the left of the subject. SD = Standard
Deviation.

 

Subject ID 10° recline 15° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A -1.7 -3.1 -2.6 -6.1 -5.3 -5.0
P2B 3.9 0.3 1.9 2.1 2.3 1.1
P2C -0.9 -2.8 -1.3 0.2 -0.9 -1.1
P2D -1.0 1.3 0.5 0.8 -0.8 1.0
P2E -0.3 -0.5 -0.4 0.2 -0.5 -0.7
P2F 0.0 0.1 1.0 -0.1 1.4 -0.9
PZG -1.2 -1.4 -1.8 0.2 0.0 —0.2
P2H 1.4 0.4 1.1 2.4 1.7 1.3
P21 -2.0 -5.2 -1.0 —0.9 -4.5 3.1
P2J -0.7 -0.4 -1.5 —2.9 -0.8 -3.0
Avg -0.2 -l.1 -0.4 -0.4 -0.7 -0.4
SD 1.7 2.0 1.5 2.5 2.5 2.3

5th percentile
females
P2K -1.7 -1.4 -1.0 -1.5 -1.7 -1.1
P2L -4.4 -3.0 -1.2 —4.8 -4.5 -2.4
P2M -1.5 -l.2 -1.5 -2.2 -1.4 -1.7
PZN -1.5 -0.8 -0.6 -1.3 -2.2 -0.6
Avg -2.3 -1.6 -1.1 -2.5 -2.5 -l.4
SD 1.4 1.0 0.4 1.6 1.4 0.8
95th percentile

males
P2U -6.0 -1.9 -2.3 -2.6 -0.5 1.6
P2V 0.8 -0.4 -4.5 -1.1 -2.4 -5.4
P2W 1.3 0.9 -0.9 0.8 1.7 0.0
P2X -6.6 —4.8 -3.3 -5.2 -5.4 -6.5
Avg —2.6 -1.6 -2.7 -2.0 -1.7 -2.6
SD 4.2 2.5 1.5 2.5 3.0 4.0
Total Avg -1.2 -1.3 -1.1 -1.2 -1.3 -1.1
SD 2.5 1.9 1.6 2.4 2.4 2.6

 

109

Table 67 : Lateral shear forces (F y) exerted on the thorax support at 20° and 24°
recline angles (vehicle seating). All forces are in Newtons. A negative sign indicates
that the force is directed laterally toward the left of the subject. SD = Standard
Deviation.

 

Subject ID 20° recline 24° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

males
P2A -7.2 -4.4 -5.4 -4.7 -5.2 -5.7
P2B -2.5 2.4 —3.1 0.0 -1.2 1.1
P2C 1.9 1.1 -0.1 -0.6 1.7 -1.2
P2D -0.5 -0.1 -0.2 -2.9 -1.7 -1.4
P2E 1.1 2.8 0.1 1.3 1.0 -0.2
P2F 3.7 -1.1 1.2 0.7 1.0 -0.6
P2G 0.5 -2.4 -1.0 1.5 0.5 0.3
P2H 1.0 -0.6 0.1 1.5 0.0 3.3
P21 -5.2 —3.9 -2.7 —1.2 -9.7 -5.6
P2J -1.1 -0.8 -0.5 -1.8 -1.8 -0.5
Avg -0.8 -0.7 -1.2 -0.6 —1.5 -1.0
SD 3.3 2.4 2.0 2.1 3.5 2.8
5th percentile
females
P2K -0.5 -0.8 -0.6 0.4 -0.2 -0.4
P2L -0.8 -3.4 —4.7 -2.9 -0.7 -2.9
P2M -6.5 —5.3 -4.4 -4.0 -4.7 -5.9
P2N —3.0 -4.8 -1.0 -2.8 —2.3 05
Avg -2.7 -3.6 -2.7 -2.4 -2.0 -2.4
SD 2.8 2.0 2.2 1.9 2.1 2.6
95th percentile
males
P2U -4.1 -8.6 -11.3 -9.2 -11.3 —12.6
P2V -4.5 -6.4 -5.7 -0.6 -8.0 -6.3
P2W -2.3 -3.1 -0.6 -3.5 -0.1 -0.7
P2X -6.9 -4.2 -4.4 -7.3 -5.3 -4.1
Avg -4.5 -5.6 -5.5 -5.1 —6.2 -5.9
SD 1.9 2.4 4.4 3.9 4.8 5.0
Total Avg -2.0 -2.4 -2.5 -2.0 -2.7 -2.4
SD 3.2 3.0 3.1 3.0 3.9 3.7

 

 

 

110

Table 68: Lateral shear forces (F y) exerted on lower back support pads at 10° and
15° recline angles (office seating). All forces are in Newtons. A negative sign
indicates that the force is directed laterally toward the left of the subject. SD =
Standard Deviation.

 

Subject ID 10° recline 15° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

 

 

males
P2A 2.7 -0.9 —1.0 0.9 1.5 0.3
P2B -1.6 -0.2 -5.9 -4.7 1.6 -2.5
P2C 4.0 2.8 2.0 1.7 1.6 0.7
P2D 1.9 1.0 0.5 1.0 2.9 1.2
P2E -0.9 1.0 0.3 -1.2 1.0 -1.4
P2F 1.8 2.7 2.9 0.7 1.0 1.5
P2G 1.2 1.4 -0.5 1.1 2.5 0.7
P2H -1.2 0.4 0.3 0.8 1.0 0.4
P21 2.2 2.2 -1.2 5.0 0.5 2.8
P2J 2.2 -0.4 0.6 1.4 1.5 1.2
Avg 1.2 1.0 -0.2 0.7 1.5 0.5
SD 1.8 1.3 2.4 2.4 0.7 1.5

5th percentile
kmflm
P2K 0.3 -2.1 -1.1 -1.3 0.8 0.4
P2L -3.5 -2.8 -0.5 -2.8 -2.0 0.7
P2M -2.9 -l .6 -3.0 -3.3 -3.6 -3.4
P2N -4.5 -2.9 -2.4 -3.6 -3.2 -5.4
Avg -2.8 -2.4 -1.7 -2.8 -2.0 -1.9
SD 1.8 0.6 1.2 1.1 2.0 3.0
95th percentile

males
P2U -3.2 -1.6 -0.9 -0.1 -0.5 2.8
P2V -2.4 -15.6 -7.8 -5.8 -12.1 -4.3
P2W -2.2 -l.6 -0.6 -2.4 —2.3 -2.7
P2X -6.6 -4.0 -8.3 -6.6 -3.7 —6.4
Avg -3.6 -5.7 -4.4 -3.7 —4.6 -2.7
SD 2.1 6.7 4.2 3.0 5.1 3.9
Total Avg -0.7 -1.2 -1.5 -1.1 -0.6 -0.7
S‘D 2.9 4.1 3.1 3.0 3.5 2.8

 

111

Table 69: Lateral shear forces (Fy) exerted on lower back support pads at 20° and
24° recline angles (vehicle seating). All forces are in Newtons. A negative sign
indicates that the force is directed laterally toward the left of the subject. SD =
Standard Deviation.

 

Subject ID 20° recline 24° recline
Pad 1 Pad 2 Pad 3 Pad 1 Pad 2 Pad 3

50th percentile

males
P2A 9.4 3.2 3.4 6.4 3.4 3.9
P28 1.2 -0.4 -1.7 -0.4 0.5 -0.9
P2C 1.9 2.8 1.3 2.7 1.4 1.0
P2D 2.8 3.0 2.4 1.9 1.1 —1.1
P2E 2.2 1.7 0.3 3.3 2.3 -0.9
P2F 2.7 2.9 0.8 0.5 2.9 3.3
P2G —0.1 -0.9 0.2 -0.1 1.4 -2.3
P2H -0.1 0.1 2.5 1.6 -0.4 -0.8
P21 -0.9 1.6 -1.7 2.2 2.8 3.1
P2] 1.0 0.2 0.4 2.6 0.3 -0.3
Avg 2.0 1.4 0.8 2.1 1.6 0.5
SD 2.9 1.6 1.7 2.0 1.3 2.2

5th percentile
females
P2K -1.7 0.9 -2.6 -0.8 0.3 -0.8
P2L -3.5 -4.0 -0.2 -2.6 -3.7 -1.6
P2M 3.0 -1.9 -1.8 2.9 -1.5 0.0
P2N -2.6 -3.2 —4.2 -3.0 -2.9 -3.2
Avg -1.2 -2.1 -2.2 -0.9 -2.0 -1.4
SD 2.9 2.2 1.7 2.7 1.7 1.4
95th percentile

males
P2U 5.1 -1.0 -2.5 -0.7 -2.2 -0.6
P2V -4.1 -0.9 -6.1 ~5.9 -3.1 2.2
P2W 1.4 -0.5 -0.7 1.4 -0.7 0.7
P2X -4.4 —1.7 -4.0 -4.1 -1.6 -6.0
Avg -0.5 -1.0 -3.3 -2.3 -1.9 -0.9
SD 4.6 0.5 2.3 3.3 1.0 3.6
Total Avg 0.7 0.1 -0.8 0.4 0.0 -0.2
SD 3.4 2.1 2.5 3.0 2.2 2.4

 

 

 

112

Table 70 summarizes the results of the statistical tests performed for the
comparison of lateral shear forces exerted on the thorax support under all conditions of

recline for all subjects (n=18). The bolded p-values indicate significant differences.

Table 70: Summary of p-values of statistical tests performed for the comparison of
lateral shear forces exerted on thorax support at all 4 recline angles. Values in bold
indicate significance (n = 18).

 

 

 

Recline Angles
10° 15° 20° 24°
Pad 1 v Pad 2 0.823 0.766 0.547 0.644
Pad 2 v Pad 3 0.548 0.749 0.940 0.621
Pad 1 v Pad 3 0.771 0.862 0.498 0.465

 

Similarly, Table 71 provides a summary of the statistical p-values computed from
the comparison of lateral shear forces exerted on each lower back support pad under all
conditions of recline for all subjects (n=18). The bolded p-values indicate significant

differences.

Table 71: Summary of p-values of statistical tests performed for the comparison of
lateral shear forces exerted on each lower back support pad at all 4 recline angles.
Values in bold indicate significance (n = 18).

 

Recline Angles
100 15° 20° 24°
Pad 1 v Pad 2 0.782 0.108 0.349 0.390
Pad 2 v Pad 3 0.702 0.872 0.092 0.645
Pad 1 v Pad 3 0.222 0.382 0.027 0.321

 

 

 

113

Force Data Summary

Tables 72 and 73 summarize the average force values (normal, vertical shear and
lateral shear) exerted on the thoracic and lower back support pads respectively. From
both, Tables 72 and 73, we observe that the vertical and lateral shear force values are
much smaller than the normal forces, lateral shear being close to zero. These observations

are made under all conditions of recline.

Table 72: Summary of average forces exerted on thorax support taking all subjects
into consideration. All force values are in N ewtons. Negative sign indicates direction
of force: inferiorly for vertical shear, left lateral for lateral shear and into the pad
for normal forces. VS = Vertical Shear, LS = Lateral Shear.

 

Redme Pad 1 Pad 2 Pad 3
Angle

Normal VS LS Normal VS LS Normal VS LS

(N) (N) (N) (N) (N) (N) (N) (N) (N)

10° -54.7 -13.5 -1.2 -55.6 -11.7 ~1.3 -51.3 -10.4 -1.0
15° -68.0 -12.8 -0.5 -67.3 -11.0 -0.6 -61.4 -10.1 04
Avg -61.4 -13.2 -0.9 -61.5 -11.4 -1.0 -56.4 -10.3 -0.7
20° -117.3 -25.1 -l.3 9121.4 -25.7 -1.7 -115.6 -24.7 -1.7
24° -128.2 -25.3 -1.2 -132.6 -26.8 -1.9 -121.2 -26.9 -1.7
Avg -122.8 -25.2 -l.3 -127.0 -26.3 -l.8 -118.4 -25.8 -1.7

 

 

 

114

Table 73: Summary of average forces exerted on lower back support taking all
subjects into consideration. All force values are in Newtons. Negative sign indicates
direction of force: inferiorly for vertical shear, left lateral for lateral shear and into

the pad for normal forces. VS = Vertical Shear, LS = Lateral Shear.

 

 

Recline

Pad 1 Pad 2 Pad 3
Angle

Normal VS LS Normal VS LS Normal VS LS

(N) (N) (N) (N) (N) (N) (N) (N) (N)

10° -58.4 -12.6 0.6 -47.6 -13.4 0.1 -56.6 -13.1 01
15° -57.9 -14.3 0.3 -49.5 -13.2 0.7 -61.0 -13.3 0.6
Avg -58.2 -13.5 0.5 -48.6 -l3.3 0.4 -58.8 -13.2 0.3
20° -99.5 -l4.9 2.1 514.9 -12.5 1.5 -96.9 -18.3 0.6
24° -98.2 -12.9 1.8 -86.7 -10.5 1.4 -105.6 -17.7 1.1

Avg -98.9 -l3.9 1.9 -85.8 -11.5 1.4 -101.3 -18.0 0.9

 

115

 

Discussion

Body Angles

Pad 1 was shown to produce maximum body recline angles as compared to Pad 2
and Pad 3 under all conditions of seat back recline, causing a greater rearward recline of
the subject’s torso with respect to the vertical plane. This was due to the greater
prominence of Pad 1 resulting in subjects positioning Pad 1 relatively forward with
respect to seat back plane as compared to the other two pads. Statistical analysis showed
that greater prominence in the lower back support pad contour resulted in higher values
of body recline angles. Generally, the BRA values were observed to be greater than their
corresponding seat back recline angles which may be due to the forward motion of the
lower back support pads causing subject’s lower back and pelvic region to be pushed
ahead resulting in slippage with respect to seat back.

A steady increase in thorax angle (that is, subjects reclined further rearward) was
observed with an increase in seat back recline angle. Variation in lower back support pad
contour did not significantly change the thorax angle values. The thorax angles obtained
in the current study were consistent with those reported from Bush2 at comparable recline

angles of 20° and 24° (Table 74).

Table 74: Comparison of thorax angles at 20° and 24° seat back recline angles.
Values correspond to the 50th percentile male anthropometric group. All values are
in degrees.

 

 

Recline Rampurawala Bush
Angle

20° 32.9 37.7

24° 36. 1 41 .5

 

 

116

Numerical data from Tables 16 and 17 indicated a steady decrease in thorax angle values
starting with the li ght-weight, shorter 5‘h percentile female anthropometric group and
moving towards the taller mid-males group. Beyond this, there is a steady increase in
thorax angles with increase in the subjects’ heights (95th percentile males). One
possibility for this trend could be the fact that both the extreme anthropometric groups,
5th percentile females and 95th percentile males, comprised of only four subjects each
while the 50th percentile group had 10 subjects. Hence, a comparison between the two
extreme anthropometric groups did not yield statistically significant results, while
comparisons involving the mid-males group (MM) did yield either significant or nearly
significant results (Tables 19 and 20).

Although there was no statistical trend seen in the comparison of pelvic angles at
the four seat back recline angles tested, the average pelvic angle values for the vehicle
seating were slightly greater than those of the office seating results (Tables 21 and 22).
This was due to the fact that an increase in recline angle as well as an inclined seat pan
allowed more rearward rotation of the pelvis resulting in a corresponding increase in
pelvic angles.

The average knee angle values for the vehicle seating were much greater than
office seating knee angles. This was once again due to the inclined footrest in
combination with the angled seat pan used in vehicle seating and also the fact that the
footrest itself was at a greater height above the ground as compared to the footrest used in
the office seating test environment. No statistically significant differences in knee angle

values were observed with variation in lower back support pad contour.

117

A comparison of knee angles between Bush’s study2 and the current research is
presented in Table 75. These knee angle values were measured at 20° and 24° seat back
recline. Results from this study were observed to be greater than the Bush study. Subjects
in the Bush study were asked to hold on to a steering wheel which may have made them
sit relatively more upright than subjects tested in the current study wherein no steering

wheel was used. As a result, the knee flexion may have reduced in the Bush study.

Table 75: Comparison of knee angles at 20° and 24° seat back recline angles. Values
correspond to the 50th percentile male anthropometric group. All values are in

 

degrees.
Recline Rampurawala Bush
Angle
20° 151 .9 136.7
24° 153.6 134.0

 

 

 

118

Lower Back Support Pad Position
Height

Even though Pad 1 was greater in length than Pad 2, the preferred heights of the
apexes above seat pan for both pads was almost the same except for the 150 recline angle
of the 50th percentile anthropometry. This was attributed to the fact that Pad 1 had a more
prominent contour as compared to Pad 2, due to which, the upper and lower ends of Pad
1 may not have come into significant contact with the subject's back resulting in Pad 1
and Pad 2 having similar effects. Also, it may be that in these preferred pad positions,
subjects’ liked the force supporting their lower backs.

Pad 3, however, with a thickness of 27 mm at apex, had a relatively flatter contour
as compared to Pad 1 whose thickness at apex was 44 mm, their lengths being almost the
same. Hence, subjects' backs were expected to have contact over a larger surface area of
Pad 3 without a feeling of discomfort. Subjects' preferred to lower the position of Pad 3 at
approximately the location of L5 and have the entire pad supporting the lumbar and
pelvic regions.

The apex location of Pad 3 is significantly lower than that of Pad 1 and Pad 2 with
respect to seat pan at all recline angles, except for the 50th percentile anthropometric
group at a 15° recline angle.

Under all conditions of recline, the apex location of all pads was below the

average anatomical location of L3 for all 3 anthropometric groups.

The diversion in results under the “50‘h percentile anthropometric group at 15°

recline angle” condition could be due to the Subject PZB. This subject preferred to

position all pads at a much lower position (average apex height above seat pan = 103

119

mm) as compared to all other nine subjects (average apex height above seat pan = 172
mm) from the same anthropometric group under all conditions of recline.

When the pad apex height above seat pan was expressed as a percentage of
subject’s Seated Height (Tables 33 and 34), a narrow range of results, 17% to 22% of
Seated Height, was observed. This indicated that even though there was a large variation
in subjects’ seated heights (Minimum: 762 mm, Maximum: 1016 mm), the position of the
lower back support pads remained relatively constant in terms of their individual seated
heights. The narrow percentage range suggested a relationship between the lower back

support pads height and the subject’s Seated Height.

120

F ore-aft Prominence

The results for fore-aft prominence positions of all pads indicated that under all
test conditions Pad 1 had the foremost position. Pad 1 had a much more prominent
contour (thickness = 44 mm) as compared to the other two pads (thickness = 27 mm).
Even in the most rearward position, the outer front surface of Pad I lay approximately 4
mm in front of the plane of the seat back. Subjects were asked whether they preferred Pad
1 to go further rearward, and most answered in the affirmative. Pad 2 and Pad 3 were
similar to one another in terms of prominence and showed similar results in terms of fore-
aft positioning.

One must note that the foremost positioning of Pad 1 does not necessarily mean
that it resulted in an increase in the contact area between the subject’s back and the pad
surface. Hence, even though there were differences observed in the fore-aft positioning of
Pad 1 and Pad 2, the lack of proper contact with Pad 1 may have resulted in its position
with respect to height above the seat pan being similar to that of Pad 2 as explained in the

previous section “Lower Back Support Pad Position — Height”.

121

Forces
Normal Forces

A study by F aiks28 measured normal forces necessary to lift a relaxed seated
person from a reclined position (20° rearward of vertical) to a vertical position. Twelve
men and women from a wide range of anthropometric groups were tested in four office
seats. Faiks did not account for, or address, torso articulation. Hence forces from the
F aiks study were averaged along the seat back at the 200 recline position for comparison.
The total normal load along the seat back at a 20° recline measured by Faiks was 227 N.
In a study23 by Bush and Hubbard, the total normal load produced by a sample of Mid
Males (50’h percentile) was 209 N at the same recline angle of 20°. The sum of thoracic
and lower back normal forces measured in the current study was calculated to be 206 N at
a 20° seat back recline, taking only the 50th percentile males anthropometric group of
subjects into consideration (n = 10). Hence, a similarity in results was observed amongst
the three studies.

However, if we consider the thoracic and lower back forces individually at this
recline angle, there exists a difference in values between the Bush study23 (182.1 N
thoracic force) and the current one (115.3 N thoracic force). Reasons could be the fact
that for the Bush study, the thoracic support was positioned at the T9 level as compared
to the T7 level for the current study. Also, the pelvic support used in the Bush study was
fixed below the location of L5, though it allowed articulation of the lower back region.
The lower back support in the current study was movable and was positioned individually
by each subject as per their comfort needs. The variation in lower back support shape

may also have had an effect on the variation in results. Also, the average weight of

122

subjects tested in Bush’s study was 170 lbs as compared to the 154 lbs average weight of
subjects belonging to the 50th percentile males anthropometric group tested in the current
study,

When evaluating the level of support a pad provides, another aspect worth
considering was the pressure. The average normal force values exerted on the lower back
support pads can be attributed to the surface area factor of each of those pads. Pressure is

related to force and surface area by the following relation:

Equation 6: Relation between pressure, force and surface area.

Pressure = Force / Area

Pads 2 and 3 have the same width; however, Pad 2 is much smaller in length as
compared to Pad 3. Hence, the surface area of Pad 2 that interfaces with the subject’s
back was less than that compared to Pad 3. By lowering the normal force exerted on Pad
2, subjects maintained relatively constant pressure values under all conditions. Pad 3
having a comparatively greater length, and hence more surface area in contact with
subject’s back, resulted in greater force values being exerted on it, keeping pressure
relatively constant as indicated by the relative similarity in average pressure values given
in Tables 58 and 59.

Pad 1 and Pad 3 have no significant difference in normal force values being
exerted on them. This is because both these pads have almost the same surface area being
exposed to the subjects’ back. In the statistical analysis part of the “Height” section, it

was mentioned that the highly prominent curvature of Pad 1 prevents its upper and lower

123

ends from completely coming into contact with the subject’s back. One may argue that if
this was the case, how was it that the forces exerted on Pad 1 and Pad 3, which had
similar lengths, were not significantly different in order to keep pressure relatively
constant? The answer to this could be that the prominent contour of Pad 1 affected its
position relative to the seat pan in a manner that enabled the subject to exert
approximately the same amount of pressure on it as that exerted on a similar-sized Pad 3.

Normal forces exerted on the lower back support pads and thorax support
expressed in terms of percentage of subject’s body weight (% BW) yielded a narrow
percentage range under all conditions of recline. This reaffirmed the fact that with an
increase in seat back recline angle there was a shift in body weight onto the seat back.
This shift in body weight was proportional to the subject’s anthropometric weight as
indicated by the narrow percentage ranges.

Normal forces exerted on the lower back support pads by the 95th percentile male
anthropometric group (Large Males, LM) yielded either significant or nearly significant
statistical results when compared with normal forces exerted by the Small Females (SF)
and Mid Males (MM) anthropometric groups. These results were observed in both the
office and vehicle seating environments (Tables 56 and 57). However, significant
differences were not found between the SF and MM groups. This may be a function of
overall weight. From Table 7, the average anthropometric weights of the SF, MM and
LM groups were 1 10 lbs, 154 lbs and 224 lbs respectively. Hence, the difference in
average weight between the SF and MM groups was 44 lbs and that between the MM and

LM groups was 70 lbs. These numbers indicated that an increase in the sitter’s

124

anthropometric weight by a value greater than 44 lb but less than 70 lb may cause a

statistically significant change in normal forces exerted on the lower back support pad.

125

Vertical Shear Forces

Even though no statistical trend was observed with regard to the exertion of
vertical shear forces by subjects on the thorax and lower back support pads, it was
interesting to note that in the case of thorax support, the vertical shear forces increased
with increase in subject’s weight. The 95"1 percentile males exerted the maximum vertical
shear forces onto the thorax support under all conditions of recline while the 5th
percentile females exerted the minimum forces under similar conditions.

However, in the case of vertical shear forces on the lower back support pads, such
a relationship between subject weight and exerted force did not hold true. From Tables 62
and 63 we observed that subjects from the 50th percentile male anthropometric group
exerted maximum vertical shear forces in both the office and vehicle seating test
environments.

These observations indicated that it was the position of the support on the seat

back that determined the value of the vertical shear forces and not the weight of the sitter.
Lateral Shear Forces

Lateral shear force values were observed to be close to zero irrespective of subject

anthropometry or recline angle. Also, no statistical trends were observed.

126

Conclusions

There are several factors that govern levels of seated comfort. These include:
user’s anthropometry (height, weight, girth etc.), design of seat (seat pan, seat back
supports, fabric cover etc.), seating environment (office, vehicle etc.), duration of being
seated, and nature of work done while seated (typing, driving, watching a movie) etc.

Most North American companies position the apex of a lumbar support
mechanism around the approximate region of the lumbar lordosis (L3)”. However, Asian
companies prefer to lower the location of lumbar support apex to accommodate for pelvic
support”. Data from this research provides insight into subject’s preference of support
and location for lower back support pads. This research suggests several parameters (as
described below) for the improved design of lower back supports for both vehicle seat
and office chair manufacturers.

The focus of the current research was to study the effects of three lower back
support pads, varying in length and prominence, on subjects belonging to three different
anthropometric groups over a range of seated postures. Data were analyzed in terms of
support position, body posture and support force levels. Subjects were given complete
control over the positioning of the support pads in a manner they deemed comfortable.
Further, the test seats did not have a fixed contour, so the results of these tests were not
influenced by seat contour. Contour can influence the allowable postures, thus affecting
contact of lower back region. For example, a forward sloping contour in the shoulder

region would prohibit a taller individual from rotating shoulders rearward, not allowing

127

for a lordotic curvature. Following are the major conclusions drawn from the results

obtained in this study.

Lower Back Support Pad Position

1. The apex of Pad 3 was positioned lower (around the L5 region) as compared to Pad 1
and Pad 2. This was attributed to the fact that Pad 3 had relatively longer length
extending from upper lumbar to pelvic region, enabling subjects to choose a lower
preferred apex position. The preferred apexes of all pads however were measured to be
below the approximate location of L3.

2. Pad apex height above seat pan expressed as a percentage of subject's seated height
resulted in a narrow percentage range, 17% to 22% of Seated Height. These data
indicated that with an increase in seated height, the lower back support pad was raised
higher above the seat pan proportional to the occupant’s Seated Height.

3. The apex of Pad 1 was positioned significantly foreword with respect to the plane of
the seat back as compared to Pad 2 and Pad 3. This however can be attributed to the fact
that Pad 1 had a much greater prominence (thickness = 44 mm) than the other two pads
(thickness = 27 mm) as a result of which the outer surface of Pad 1 protruded beyond the
seat back plane even in the rearmost position unlike Pad 2 and Pad 3 which could be

positioned rearward of the seat back plane.

128

Forces

1. Pad 3 had the greatest normal forces exerted on it while the smaller length Pad 2 had
the least. The normal forces on Pad 2 were significantly lower than those on the other two
pads.

2. Pressures on the pads were computed using the forces and total pad surface area data.
Complete contact with the pad was assumed. Similarity in results indicated the ability of
subjects to maintain a relatively constant pressure on the three pads under all conditions
of recline, that is, with an increase in length (and hence contact surface area) of the
support pad, the forces on it increased in order to maintain a relatively constant force/area
(pressure) ratio.

3. Normal forces exerted on lower back support pads expressed as a percentage of
subject’s body weight (BW) yielded narrow ranges for both office (6% to 10% of BW)
and vehicle (12% to 16% of BW) seating environments. The increase in %BW seen from
office to vehicle seating tests is due to the relative increase in shift of body weight onto
the seat back caused by an increase in seat back recline angle.

4. The data suggest that the magnitude of vertical shear forces on the lower back support
pads depends on the position of these pads relative to the seat back and seat pan and not
on the subject’s weight. This is because it was the 50th percentile male group that exerted
the maximum vertical shear forces. In fact, in the vehicle seating, the average vertical
shear forces exerted by the light-weight 5’h percentile females were greater than the
forces exerted by the heavy-weight 95th percentile males.

5. As expected, due to the sagittal and symmetric nature of the tasks, lateral shear forces

were least dominant and close to zero in magnitude.

129

Body Angles

1. Body Recline Angle (BRA) varied directly with the foreword prominence of lower
back support, that is, greater the foreword position of the support pad with respect to the
plane of the seat back, greater were the body recline angle values.

2. Thorax angles increased with increase in seat back recline angle. However, the design
contour and positioning of lower back support pads had no significant effects on the
thorax angle values. The 95’h percentile female anthropometric group had the maximum
thorax angles while the 50‘h percentile males group exhibited the least thorax angle
values. Lower thorax angle values indicated a lesser recline with respect to the vertical.
3. Knee angles for the vehicle seating postures were significantly greater than those for
the office seating. However, little variation in knee angles was computed between the two
recline angles tested for each seating environment, office and vehicle. These results
indicated that variation in seat back recline angle had little or no effect on knee angles. It
is the raise in height of the vehicle seating footrest surface that caused a significant

increase in knee angle values coupled with the effect of an inclined seat pan.

130

13.14

Studies by Akerbloml0 and Andersson suggested that lower back supports
should be positioned at approximately the fifth and third lumbar vertebrae respectively.
Their results were limited by the fact that they used a single lower back support. In this
research, the usage of three different lower back supports varying in length and
prominence indicated that it is the size of the support that determines where the occupant
prefers to position it. Shorter length back support (Pad 2) was preferred to be positioned
at just below the L3 level while longer length support (Pad 3) was positioned just below
the location of L5, providing support to both the pelvic and lumbar regions. Andersson’s
studies involved pre-determined positions of back support in terms of fore-aft and height
above seat pan. Porter and Norris”, though allowed vertical height adjustment of back
supports, restricted horizontal prominence to distances of 0, 20 and 40 mm with respect
to the seat back. In the current research, all movements of the back support pads were
entirely controlled by the subjects and positioned as per their preference. All though
subject preferences were included in Reed’s study"), his work was only based on vehicle
seating test environment.

Support forces measured by F aiks and Reinecke20 indicated a sharper rise in force
change for the thoracic region (2.5 N force for every degree of backrest inclination) as
compared to the lumbar region (0.6 N force for every degree of backrest inclination).
Although a similar trend was observed in the current study, there was a difference in
numerical values. The force change for the thoracic region was measured to be 6.4 N for
every degree as compared to 3.9 N in the lumbar region.

In essence, the current research presents a simple though relatively complete

approach in determining what the occupant desires in terms of lower back supports. The

131

protocols followed in this research have covered some of the limitations posed in

previous studies and the results obtained indicated certain differences as discussed above.

Future Work

A study similar to the current one could be carried out with a larger and more
varied pool of subjects to get more valid statistical results. The inclusion of subjects from
varied age groups could be considered due to the significant effect of age on vertebral
disc anatomy. Also, lower back supports both with and without a fabric cover could be
used as part of the test protocol for comparison of resultant forces. A similar test protocol
could be carried out over longer duration experimental tests as compared to the short

duration tests included in Phase 2 of the current research.

132

l 0.

11.

12.

13.

Bibliography

Herman Miller Inc, Body Support in the Office: Sitting, Seating and Low
Back Pain, internal documents, Zeeland, Michigan, 2002

Bush TR, Posture and Force Measures of Mid-Sized Men in Seated Positions,
PhD Thesis, Michigan State University, East Lansing, Michigan, 2000

Matt G, A Patient's Guide to Lumbar Spine Anatomy, Spine Lumbar, 2002

Pope M, Andersson GB, F rymoyer F, Chaffin D, Occuptional Low Back
Pain: Assessment, Treatment and Prevention, New York, 1991

Dowell WR, Yuan Fei, Green B, Office Seating Behaviors, an Investigation of
Posture, Task and Job Type, Proceedings of the Human Factors and
Ergonomic Society 45tll Annual Meeting, Minneapolis, Minnesota, 2001

Kelsey J L, Pastides H, Bisbee GE et al., Musculoskeletal disorders: Their
frequency of occurrence and their impact on the population of the United
States, Journal of Community Health, Volume 14, New York, 1978

National Safety Council, Accidents facts for 1992, Chicago: National Safety
Council, 1992

Andersson GBJ, The epidemiology of spinal disorders: The adult spine,
Principles and Practices, Raven press, New York, 1991

Snook SH, Approaches to the control of back pain in industry, Spine: State
of the Art Reviews 2, Spine, 1987

Akerblom B, Standing and sitting posture with special reference to the
construction of chairs, Doctoral Dissertation, A.B. Nordiska Bokhandeln,
Karolinska lnsitutet, Stockholm, 1948

Keegan JJ, Alterations of the lumbar curve related to posture and seating,
Journal of bone and Joint Surgery, 35-A(3), 589-603, Needham,
Massachusetts, 1953

Keegan JJ, The medical problem of lumbar spine flattening in automobile
seats, SAE Technical Paper 838A, New York, Society of Automotive
Engineers, 1964

Andersson GBJ, Otengren R, Nachemson A, and Elfstrtim G, Lumbar disc
pressure and myoelectric back muscle activity during sitting: 1. Studies on an

133

14.

15.

1. 6.

17.

18.

19.

20.

21.

22.

23.

24.

experimental chair, Scandinavian Journal of Rehabilitation Medicine, 6(3),
104-114, 1974

Andersson GBJ and Otengren R, Lumbar disc pressure and myoelectric
back muscle activity during sitting: 11. Studies on an office chair,
Scandinavian Journal of Rehabilitation Medicine, 6(3), 115-121, 1974

Andersson GBJ and Otengren R, Lumbar disc pressure and myoelectric
back muscle activity during sitting: III. Studies on a wheelchair,
Scandinavian Journal of Rehabilitation Medicine, 6(3), 122-127, 1974

Andersson GBJ, Otengren R, N achemson A, and Elfstrtim G, Lumbar disc
pressure and myoelectric back muscle activity during sitting: IV. Studies on
a car driver’s seat, Scandinavian Journal of Rehabilitation Medicine, 6(3),

128-133, 1974

Andersson GBJ, Murphy R, Otengren R and N achemson A, The influence of
backrest inclination and lumbar support on lumbar lordosis, Spine, 4(1), 52-
58, 1979

Porter JM and Norris BJ, The effects of posture and seat design on lumbar
lordosis, Contemporary Ergonomics, New York, 191-196, 1987

Reed MP, Schneider LW and Eby B, The Effects of Lumbar Support
Prominence and Vertical Adj ustability on Driver Postures, University of
Michigan Transportation Research Institute, Ann Arbor, Michigan, 1995

F aiks F and Reinecke S, Supporting the lumbar and thoracic regions of the
back during sitting, Steelcase document, Grand Rapids, Michigan, 1998

Goossens RHM, Snijders CJ, Roelofs CY and van Buchem F, Free shoulder
space requirements in the design of high backrests, Ergonomics, Vol 46, N0
5, 518-530, Taylor and Francis Group, London, 2003

Carcone SM and Keir PJ, Effects of backrest design on biomechanics and
comfort during seated work, Applied Ergonomics, 38, 755-764, Elsevier,
Oxford, 2007

Bush TR and Hubbard RP, Support force measures of midsized men in
seated positions, Journal of Biomechanical Engineering, ASME, Vol. 129,
2007

Claire CG et al., 1988 Anthropometric Survey of US Army Personnel :
Summary Statistics Interim Report, Anthropology Research Project Inc,
Yellow Springs, Ohio, 1988

134

25.

26.

27.

28.

29.

Qualisys MacReflexTM Motion Measurement System User Manual, 1995

Bush TR and Gutowski PE, An approach for hip joint center calculation for
use in seated postures, Journal of Biomechanics 36, 1739-1743, Elsevier
Science Ltd, 2003

Seidel GK, Marchinda DM, Dijkers M, Soutas-Little RW, Hip joint center
location from palpable bony landmarks — a cadaver study, Journal of
Biomechanics 28, 995-998, Elsevier Science Ltd, 1995

F aiks F and Reinecke S, Investigation of Spinal Curvature while Changing
One’s Posture During Sitting, Contemporary Ergonomics, Taylor and

Francis Group, London, 1998

Openshaw S and Taylor E, Ergonomics and Design — A Reference Guide
from Allsteel Inc, Muscatine, Iowa, 2006

135

   

“1171117111711117117111111.1111: