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POSITION, FORCE, AND PRESSURE MEASURES OF THE
BODY IN VARIOUS CYCLING POSTURES

presented by

Chisom S. Wilson

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POSITION, FORCE, AND PRESSURE MEASURES OF
THE BODY IN VARIOUS CYCLING POSTURES

By

Chisom S. Wilson

A THESIS

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

MASTER OF SCIENCE

Department of Mechanical Engineering

2006

Abstract

POSITION, FORCE, AND PRESSURE MEASURES OF THE BODY IN VARIOUS
CYCLING POSTURES

By A
Chisom S. Wilson

Non-traumatic injuries speciﬁc to bicyclists may be linked to forces present at the
interfaces between the cycle and rider. These injuries include weakness and numbness of
the hands and wrists, soreness of the pelvis, skin problems in the groin, erectile
dysfunction and impotence.

The ﬁrst goal of this investigation was to measure the forces present at the
rider/cycle interfaces. Vertical and shear loads were measured for ten (10) subjects in a
common ﬁt position. The crank arm angles at which the maximum and minimum forces
occurred were also obtained using a motion analysis system, and regions of rider contact
with the seat were visualized with a pressure mapping system.

The second goal was to determine the effects of different hand positions on
measured interface forces. Vertical and shear loads were measured after moving the
handlebars 5cm closer to, then 5 cm further from the subject. A statistical analysis was
performed using the SAS Mixed procedure with a signiﬁcance level a = 0.05. Several
forces were signiﬁcantly affected by changing the cycle’s handlebar position.

Vertical loads were greater than shear loads, and in combination they may be
contributing factors in non-traumatic injuries at the groin and hands reported by

bicyclists.

Copyright by
Chisom S. Wilson

2006

Dedication

I would like to dedicate this thesis to my wife Jennifer, and to my family, Johnny,
Sandra, Chelsea, and Chesney Wilson. Your belief in me instilled the dedication and

conﬁdence necessary to complete this work.

iv

Acknowledgments

I would like to thank my advisor Dr. Tamara Reid Bush for her advice, ideas, and
patience throughout the development and completion of this investigation. I would also
like to thank my committee members Drs. Robert Hubbard and Dahsin Liu for their
support, input, and suggestions.

To Dr. Joseph Vorro, your clarifying of the anatomy of the human body was
immensely helpful.

Finally, I would like to thank Aaron Huber, Thomas Schneider, Cleveland
Thrasher, Nathan Remsberg, Jennifer Langridge, and Bethany Danielski. I would not

have gotten through this without all of your help.

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................... viii
LIST OF FIGURES ............................................................................................... xii
Introduction and Literature Review ........................................................................ l
Bicycling Related Injuries ................................................................................... 1
Engineering Perspective ...................................................................................... 4
Bicycling Posture ................................................................................................ 6
Scope of Research ............................................................................................... 8
Methods ................................................................................................................. 10
Test Equipment ................................................................................................. 10
Experimental Stationary Bicycle ................................................................... 10
Load Cells ..................................................................................................... 13
Motion Capture ............................................................................................. 14
Pressure System ............................................................................................. 16
Subject Recruitment and Selection ................................................................... 17
Testing ............................................................................................................... 19
Subject Targeting .......................................................................................... 19
Equipment Preparation .................................................................................. 24
Initial Device Setup ....................................................................................... 27
Test Descriptions ............................................................................................... 28
Measure of Ischial Tuberosities .................................................................... 28
Cycling Tests ................................................................................................. 28

vi

Analysis ................................................................................................................. 3 1

Results ................................................................................................................... 37
Pedal and Crank Tangent Forces ................................................................... 39

Seat Vertical Forces ...................................................................................... 49
Forward/Rearward Seat Forces ..................................................................... 56
Lateral Seat Forces ........................................................................................ 62

Seat Pressure Mapping .................................................................................. 67
Handlebar Vertical Forces ............................................................................. 69
Handlebar Forward/Rearward Forces ........................................................... 74
Handlebar Lateral Forces .............................................................................. 80
Signiﬁcant Effects due to Changes in Handlebar Position ............................... 86
Pedal Measures .............................................................................................. 86

Seat Measures ................................................................................................ 88
Handlebar Measures ...................................................................................... 93
Discussion and Conclusions .................................................................................. 97
Baseline Rider/Cycle Interface Seat and Handlebar Forces .............................. 97
Seat Forces .................................................................................................... 97
Handlebar Forces ......................................................................................... 101
Timing Angles ............................................................................................. 102
Signiﬁcant Effects from Changes to Handlebar Position ................................ 104
Pedal Data Comparisons ............................................................................. 106
References ........................................................................................................... l 10

vii

LIST OF TABLES

Table 1: Male Subject Anthropometry ............................................................................. 18
Table 2: Subject Targeting Table ..................................................................................... 21
Table 3: Average Pedal Force Component Tangent to Crank Arm Path .......................... 42

Table 4: Angle at which the Applied Maximum and Minimum Force Component Tangent

to the Left Crank Arm Path Occurred (Timing Angle) ............................................. 43
Table 5: Lateral (side to side) Right and Left Pedal Maximum Forces; ........................... 44
Table 6: Timing Angle of Maximum Lateral Pedal Force ................................................ 45
Table 7: Minimum Right and Left Pedal Lateral Forces; ................................................. 46
Table 8: Timing Angle of Minimum Lateral Pedal Forces ............................................... 47
Table 9: Range between Maximum and Minimum Lateral Pedal Forces ......................... 48
Table 10: Maximum Seat Vertical Force and Standard Deviation (SD) .......................... 50
Table 11: Timing Angles at which the Maximum Vertical Seat Forces Occurred .......... 50
Table 12: Minimum Seat Vertical Force and Standard Deviation (SD) ........................... 52
Table 13: Timing Angle of Minimum Seat Vertical Forces ............................................. 53
Table 14: Range between the Maximum and Minimum Vertical Seat Forces ................. 55

viii

Table 15:

Table 16:

Table 17:

Table 18:

Table 19:

Table 20:

Table 21:

Table 22:

Table 23:

Table 24:

Table 25:

Table 26:

Table 27:

Table 28:

Table 29:

Table 30:

Table 31:

Maximum Forward/Rearward (FR) Seat Force ............................................... 57
Maximum Forward/Rearward Seat Force Timing Angles ................................ 58
Minimum FR Seat Shear Forces; ..................................................................... 59
Range between the Maximum and Minimum FR Seat Forces ......................... 61
Maximum Lateral Seat Forces; ........................................................................ 65
Lateral Seat Force Timing Angles .................................................................... 66
Range of Maximum Lateral Seat Forces ........................................................... 66
Maximum Handlebar Vertical Force; .............................................................. 69
Timing Angle of the Maximum Vertical Handlebar Force ............................... 70
Minimum Handlebar Vertical Force ................................................................. 72
Timing Angle of the Minimum Vertical Handlebar Load ................................ 73
Range between the Maximum and Minimum Vertical Handlebar Forces ........ 74
Maximum FR Handlebar Forces ....................................................................... 75
Timing Angle of the Maximum FR Handlebar Force .............................. A ......... 76
Minimum FR Handlebar Forces; ...................................................................... 78
Minimum Handlebar FR Force Timing Angles ................................................ 79
Range between the Maximum and Minimum FR Handlebar Forces ................ 80

ix

Table 32: Maximum Lateral Handlebar Forces ................................................................ 81

Table 33: Maximum Handlebar Lateral Force Timing Angles ......................................... 82
Table 34: Minimum Lateral Handlebar Forces ................................................................. 83
Table 35: Minimum Lateral Handlebar Force Timing Angles ......................................... 84
Table 36: Range between the Magnitude of the Maximum and Minimum ...................... 85

Table 37: Mean Pedal Forces That Showed a Statistically Signiﬁcant Difference at ....... 87
Table 38: Probability of Zero Difference in Pedal Forces ................................................ 87

Table 39: Pedal Force Timing Angles That Showed a Statistically Signiﬁcant Difference
of P < 0.15 for at Least One Handlebar Position Change, i.e. Close-Far, Close-
Regular, or Far-Regular ............................................................................................. 87

Table 40: Probability of Zero Difference in Pedal Force Timing Angles ......................... 88
Table 41: Mean Seat Forces That Showed a Statistically Signiﬁcant Difference at ......... 89

Table 42: Mean Seat Forces in %BW that showed a Statistically Signiﬁcant Difference of
P< 0.15 for at Least One Handlebar Change, i.e. Close-Far, Close-Regular, or Far-
Regular ...................................................................................................................... 90

Table 43: Probability of Zero Difference in Seat Forces .................................................. 91

Table 44: Mean Seat Force Timing Angles That Showed a Statistically Signiﬁcant
Difference of P < 0.15 for at Least One Handlebar Position Change, i.e. Close-Far,
Close-Regular, or Far-Regular .................................................................................. 92

Table 45: Probability of Zero Difference in Seat Force Timing Angles ........................... 92

Table 46: Mean Handlebar Forces That Showed a Statistically Signiﬁcant Difference at
P<0.15 for at Least One Handlebar Position Change, .............................................. 93

Table 47: Mean Handlebar Forces in %BW that Showed a Statistically Signiﬁcant
Difference of P< 0.15 for at Least One Handlebar Change, i.e. Close-Far, Close-
Regular, or F ar-Regular ............................................................................................. 94

Table 48: Probability of Zero Difference in Handlebar Forces ........................................ 95

Table 49: Mean Handlebar Force Timing Angles That Showed a Statistically Signiﬁcant
Difference of P < 0.15 for at Least One Handlebar Position Change, i.e. Close-Far,
Close-Regular, or F ar-Regular .................................................................................. 96

Table 50: Probability of Zero Difference in Handlebar Force Timing Angles ................. 96

xi

LIST OF FIGURES

Figure 1: Cyclist Positioned to Obscure the Axle of the Front Wheel with the Top of the

Handlebars ................................................................................................................... 8
Figure 2: Stationary Cycling Apparatus ............................................................................ 10
Figure 3: Cycle crank arm and pedal surface .................................................................... 12

Figure 4: Anterior Target Locations

http://members.aol.com/Attic2 l/Anatomy/skeletonl .html (8/21/2006) ................... 22
Figure 5: Posterior Target Locations ................................................................................. 23
Figure 6: Left Pedal -- Spindle and Back Pedal Targets .................................................. 24
Figure 7: Cycle Seat and Load cell ................................................................................... 26
Figure 8: Cycle Seat Height Adjustment ........................................................................... 27
Figure 9: Laboratory (Global) Coordinate System; .......................................................... 31

Figure 10: Example of a Coordinate System Transformation from Unprimed to Primed
Coordinates ................................................................................................................ 32

Figure 11: Vector Describing the Left Pedal’s Surface Orientation that was Used to
Rotate the Left Pedal Forces into the Laboratory Coordinates; X’-axis into the paper

................................................................................................................................... 33
Figure 12: Deﬁnition of the Radial and Tangent Crank Arm Directions, as well as the

Crank Arm Angle as Viewed from the Left Side of the Cycle ................................. 35
Figure 13: Work and Power Done by Pedal Forces .......................................................... 39

xii

Figure 14: Proﬁle of the Left Pedal Force Tangent to the Crank Arm Path; Single trial,

single subject ............................................................................................................. 40
Figure 15: Positive and Negative Work on Pedal ............................................................. 40
Figure 16: Vertical Seat Force Proﬁle over Five Crank Arm Revolutions; ...................... 49
Figure 17: Maximum Vertical Seat Force Timing Angle Histogram ............................... 51
Figure 18: Minimum Seat Vertical Force Timing Angle Frequency ................................ 54

Figure 19: Forward/Rearward (FR) Seat Force Proﬁle over Five Subsequent Crank Arm

Revolutions; Single trial for one subject ................................................................... 56
Figure 20: Histogram of Minimum FR Seat Force Timing Angles .................................. 60
Figure 21: “Double Hump” Lateral Seat Force Proﬁle; ................................................... 63
Figure 22: "Single Hump" Lateral Seat Force Proﬁle; ...................................................... 64

Figure 23: Top View of Seat Pressure Maps; Regions of greatest contact (pressure > 3.1
N/cmz) at the maximum vertical seat force while the left leg was driving ............... 67

Figure 24: Seat Pressure Map; Timing of the maximum FR and lateral seat forces. Gre
regions indicated the greatest contact areas between the seat and rider (>3.1 N/cm )
................................................................................................................................... 68

Figure 25: Handlebar Vertical Force Proﬁle; Single subject ............................................ 71
Figure 26: Frequency of Right Maximum Vertical and FR Handlebar Timing Angles 77

Figure 27: Representative Crank Torque Proﬁle for One Crank Revolution in a Single
Subject; Smak et al. (1999), Figure 1(a) ................................................................. 108

xiii

Introduction and Literature Review

Bicycling Related Injuries

For millions of people worldwide bicycle riding is a popular activity, enjoyed as a
means of transportation, recreation, exercise, and sport. The health beneﬁts of physical
activity, including bicycling, have been well examined and documented. Moderate
physical activity may lead to a reduced risk of premature mortality, heart disease, and
diabetes (National Center for Health Statistics 2005).

Along with the health beneﬁts, risks associated with bicycling and include both
traumatic and non-traumatic injuries. Traumatic injuries to the head, skin, and limbs may
occur from accidents such as falling off the bicycle and collisions with other cyclists,
pedestrians, or motor vehicles. These injuries of bicyclists are typically treated through
clinically standard treatments of traumatic injuries, as described in trauma literature
(Mellion 1996).

Non-traumatic injuries associated with bicycling are also common and generally
more clinically challenging to diagnose. These may include skin imitation and various
musculoskeletal pains, with physicians attributing them to incorrect positioning, incorrect
mechanics, and/or overuse (Mellion 1996, Weiss 1994).

Assuming that incorrect mechanics plays a role in non-traumatic injury,
engineering research in bicycling biomechanics may help bridge the gap between simply
studying “what hurts and where” and correction of the mechanics as viewed from a
clinical standpoint. For example, biomechanics research has been helpful in elucidating

the knee joint loads generated while riding a bike (Gregersen and Hull 2003) and

revealing potential mechanics anomalies in those bicyclists experiencing overuse knee
injuries (Bailey et al. 2003).

Over the last several years there has been an increased interest in non-traumatic
cycling related injuries speciﬁc to the interfaces of the bicycle and rider. Weakness and
numbness in the hands and wrists, burning of the feet, soreness of the pelvis and ischial-
tuberosities (ITs), and skin problems of the groin that include bruising, chaﬁng, boils, or
ulceration (Weiss 1985, Andersen and Boviml997) have been reported in recreational
bicyclists. The development of perineal nodular indurations, or “accessory testicles,” in
the groin of elite and professional racing cyclists has also been reported (Vuong et al
1988, Kohler et al. 2000). Vuong et al. (1988) found these nodules to be pseudocysts that
formed along the medial (inner) side of the ischial tuberosities of the pelvis, and were
attributed to the repeated micro-trauma of the stretched fascia in the perineum during
cycling. Necrotic (dead) tissue was also found around the edges of these indurations. Of
all of the contact points, non-traumatic skin injuries at the rider/seat interface are the most
frequently reported and discussed (Weiss 1994, Mellion 1996).

These injuries indicate tissue degeneration through compression and shear loading
(stress), deformation (strain), and eventual breakdown during prolonged cycling activity.
Extrinsic factors including pressure (Kohler et al. 2000), shear, temperature, and moisture
(Weiss 1994) have been attributed to cause these injuries, and are similar to factors
thought responsible in the development of decubitous ulcers (also called “pressure”
sores) in the disabled (Hobson 1992, Edsberg et al. 1999, Bennet et al. 1979). Normal

forces have been shown to be primary in reducing arterial blood ﬂow to the skin of the

palm, but normal force magnitudes necessary to occlude blood ﬂow were halved when
combined with shear loading (Bennet et al. 1979).

Andersen and Bovim (1997) reported that 32 out of 160 ( 19%) respondent male
participants in a long distance (540km) bicycle tour experienced weakness in the hands,
while 67 (40%) reported numbness or “pins and needles” (paresthesias) in the hands and
wrists. During the same bicycle tour, 33 (21%) of the male respondents reported
numbness of the genitals, primarily on the penis. In an earlier and similar report by
Weiss (1985), 12 out of 113 (11%) male and female respondents reported speciﬁc groin
problems and of those, 81% reported numbness or paresthesias. Signiﬁcant hand
problems were also reported by about 10% of the survey respondents. From a study of
463 cyclists competing in at least one 320 km cycling event, Dettori et al. (2004) reported
groin numbness by 31% of their respondents.

Potentially a more serious groin injury, epidemiological surveys have reported
instances of male erectile dysfunction (ED) and impotence (inability to achieve an
erection) in men who ride bicycles. Andersen and Bovim (1997) found that 21 of their
160 respondents (13%) reported impotence, and Dettori et al. (2004) reported that 4.2%
of the respondents suffered ED at least one week aﬁer a long distance ride, while 1.8%
continued to suffer after at least one month. They found ED to be strongly associated
with groin numbness even though all were free of ED before the event. Groin numbness
and/or pain may or may not be present with ED and impotence.

The underlying mechanisms of male groin numbness and ED may be a
combination of nerve and blood ﬂow problems, as they are sometimes present together in

bundles. Nerve entrapment has been indicated as a possible culprit leading to decreased

sensitivity and a feeling of numbness in both the hands/wrists (Capitani and Beer 2002,
Richmond 1994) and genitalia (Andersen and Bovim 1997, Weiss 1994). Riding a
bicycle with traditional seat shapes have shown a reduction of the normal blood ﬂow
characteristics, and may have resulted from arterial occlusion during times of increased
pressure on the groin while on a bicycle seat (Lowe et al. 2004, Munarriz et a1. 2005,
Nayal et a1. 1999). As such, bicycle seat designs have been modiﬁed to include extra
padding, as well as cutout areas to reduce compression on the groin/perineum. Breda et
al. (2005) showed that cyclists using a speciﬁc cutout saddle (Selle SMP) maintained
higher levels of transcutaneous (on the surface of the skin) penile oxygen saturation
compared to those on a traditional seat, which was an indicator of increased blood flow.
Interestingly, these seat designs may not minimize the incidence of ED or
impotence. Cyclists using padded seats have reported more symptoms of irritation to the
buttocks (Weiss 1985). Also, Dettori et al. (2004) found that men riding cutout saddles,
which were designed to relieve pressure on the groin (and speciﬁcally the perineum),
showed a slightly higher risk for ED alone, as well as increased risk for the combination
of groin numbness and ED together. They also found a continued relationship between
cutouts and ED even when considering those that reported pre-ride numbness. Riding a
bicycle with the handlebars even with or higher than the seat also increased risk of ED,
possibly indicating that the higher riding position relieved the hands and loaded the

buttocks more.

Engineering Perspective

As with many seating related studies, from an engineering perspective bicycling

studies have typically used some measure of interface pressure to characterize loading at

4

the interfaces. Pressure data have been evaluated using peak and mean surface pressures
on different bicycle seats (Lowe et al. 2004) and in different hand positions (Bressel and
Cronin 2004). Shear loading has been mentioned as playing a possible role in skin
injuries (Hobson 1992, Edsberg et al.1999, Weiss, 1994) but quantitative data has rarely
been reported at the interface of the seat and rider, and to our knowledge not in the
context as a potential tissue injury mechanism for bicyclists.

It has been shown that skin tissue over bony prominences previously subjected to
pressure exhibits a subsequent change in its tensile mechanical properties (Edsberg et al.
1999) and it may be reasonable to assume a similar effect holds true for the skins shear
properties. Skin over bone has also shown a lower tolerance to locally applied pressure
in terms of reducing transcutaneous (on the surface of the skin) partial pressure oxygen
measurements (Sangeorzan et al. 1989), as tissue pressure levels below the skin
(subcutaneous) increased more rapidly than when skin is loaded over muscle.

Measurement of the interaction forces present at the interfaces of the bicycle and
rider are limited to three studies accessible to this author. Bolourchi and Hull (1985)
measured one force component at the seat, three at the pedals, and two at the handlebars
in three subjects. They noted that at the time they were unaware of any other data of this
kind, and indicated their research to be important in bicycle component design, as well as
furthering knowledge of the biomechanical analysis of the pedaling process by collecting
data across different pedaling frequency values. They reported “typical” data for one
subject only and calculated the forward/rearward shearing force from an energy balance
assuming symmetry from the right to leﬁ pedals and handlebars, but suggested this load

should be measured in any future work.

Stone and Hull (1995) reported three force components at the seat, two at the
handlebars, and three at the pedals, and attempted to ﬁnd a linear relationship between a
rider’s weight and the maximum rider induced interface loads, again in the interest of
frame and component design to obtain minimum weight and acceptable reliability. Five
subjects were tested on a bicycle that was adjusted closely to their individual setups.
Stone and Hull (1995) found a strong correlation between the in-plane seat loads
(forward/rearward and vertical) and body weight.

It is interesting that although the studies above reported that these load
components were important to frame and component design, equivalent forces must also

be resisted somewhere within a bicyclist’s body tissues.

Bicycling Posture

Much work has been done on the biomechanical aspects of cycling and
performance, especially with respect to “correct” positioning (posture) in terms of seat
height above the pedals, to gain maximum beneﬁt of the muscular power developed in
the lower limbs and back. Research has dealt with the effects on pedal loading resulting
from prolonged cycling (Sanderson and Black 2003), as well as the effects of seat height
on oxygen consumption (N ordeen-Snyder 1977). The power curve generated during a
cycle of each leg shows a region of both positive and negative contributions to the
average driving power produced (Neptune and Herzog 1999), and efﬁcient pedaling
cadence frequencies have been optimized with regards to energy consumed (Foss and
Hallen 2005).

There exist little more than suggestions on the “correct” reach or “posture length”

(de Vey Mestdagh 1998) ﬁ'om the seat to handlebars, and recommended methods are

6

based solely on anthropometrical relations. For example, one method suggests that when
placing the elbow at the tip of the seat, a correct reach to the handlebar will cause tip of
middle ﬁnger to bisect the center of lateral portion of the handlebar (Richmond 1994).
This method was the starting point of a qualitatively assessed comfort survey by
Christians and Bremmer (1998), and to our knowledge no quantitative data exist that
report handlebar and seat loading in various postures deﬁned by the reach from the seat
to handlebars. De Vey Mestdagh (1998) pointed out, “. .. no matter what cycling posture
is adopted, the upper body is used in an unusual manner.” He then presented tabular data
for “posture length” from the back of the seat to the handlebars based on a combination
of the arm and torso length. These recommendations appeared to be based on visual
observations of racing cyclists.

In commercially built bicycles, an appropriate frame size provides the rider with
approximately one to two inches of clearance from the crotch to the top of the frame
when straddling the bicycle in bare feet. Correct seat height above the pedals is then ﬁne
tuned with an adjustable seat post. The length of the frame is sealed with its height, so
adjustments in the reach to and height of the handlebars, relative to the seat, are provided
through different stem lengths (Mellion 1996). Setting the correct reach is important for
correct distribution of the body weight between the front and back wheels, and is
important for maneuvering (Phinney and Carpenter 1992).

One commonly used method in bicycle shops for attaining an initial seat to
handlebar length is to have the subject ﬁrst place their hands in the lowest (drop) section
of the handlebars, and in their line of sight through the top section of the handlebar the

axle of the front wheel should be obscured (Figure 1). Stems of different lengths are then

Figure l: Cyclist Positioned to Obscure the Axle of the Front
Wheel with the Top of the Handlebars

     
 

Line of sight
\

Top section of
handlebar

Axle of front
wheel

ﬁt to the frame to accomplish this task. This method for setting the “correct” reach to the
handlebars was also recommended by Phinney and Carpenter (1992).

Ashe et al. (2003) reported that body posture, and speciﬁcally reach, affected the
untrained cyclist’s performance measures of maximum oxygen uptake and mechanical
efficiency. A study of EMG activity (Bressel and Larson 2003) of the triceps brachii in
different handlebar positions showed signiﬁcant differences in muscle activation between
the top and drop handlebar positions, possibly indicating a shift in the force system
supported by the hands at the handlebars. Changes to the cycling posture affected
through changes in the reach from the seat to the handlebars may relieve some of the

reported non-traumatic injuries through a reduction in the forces.

Scope of Research

The ﬁrst goal of this investigation was to establish baseline interface force values

and crank arm angles when those forces occurred (timing angles) during the cycling

activity for cyclists ﬁt using an approach used in commercial environments to adjust the
handlebars to the correct reach from the seat. It is theorized that these forces may
contribute to the occurrence and severity of non-traumatic injuries commonly reported in
the groin and hands of bicyclists.

The second goal was to determine if changes in the seat to handlebar length would
affect the interface forces at the seat and handlebars. As there is only a limited range of
stem lengths available, adjustability of approximately 5cm in either direction of a factory-
installed stem are the maximum adjustment before necessitating a change in frame size.

The third goal was to make comparisons with pedal force data presented by other
authors. This would conﬁrm the validity of the methodology and test equipment used for
this work.

To our knowledge, this is the ﬁrst reported attempt to measure all interface loads
during bicycling in several postures induced by changing the distance from the

handlebars to the seat.

Methods

Test Equipment

Experimental Stationary Bicycle

A custom measurement device was developed and built by modiﬁcation of a
commercially available bicycle with a “mixte”, or women’s style frame design. The
bicycle was mounted into a Velodyne stationary cycling device to allow riding the

standard bicycle indoors (Figure 2). The front wheel was removed and the forks clamped

Figure 2: Stationary Cycling Apparatus

 

into the Velodyne, making it unnecessary for the rider to maintain his or her balance to
keep the bicycle upright. The Velodyne also clamped the axle of the rear wheel, and the
tire ran on a metal roller assembly attached through a shaft to an electronically braked
unit and a 20 lb. ﬂywheel. The ﬂywheel was used to simulate inertial characteristics
comparable to actual cycling on the road, and the tire was inﬂated to approximately 0.621
N/mm2 (90 PSI) for each test.

Mounting the bicycle into the Velodyne elevated its height approximately 15cm
(6 in.) above the laboratory ﬂoor. Although the complete device was stable once
assembled, the “mixte” bicycle frame was chosen as a safety precaution as it allowed
subjects the option of stepping through the frame rather than throwing the leg around the
back of the seat when mounting and dismounting the device. There were also added
beneﬁts as stepping through the frame reduced the risk of disrupting the connection
cables for the data acquisition equipment. Modiﬁcation of the bicycle did not change its
core functionality of transforming rotational motion from the legs of the rider into
translational motion of the rider and cycle.

To maintain adjustability for sized subjects, the device’s seat allowed vertical
movement to accommodate riders of different leg lengths, and the handlebars, or grips
were modiﬁed to separate the loadings of the left and right hands. Importantly, the
handlebars were modiﬁed to maintain a standard grip width of 42cm while they allowed
fore/aft and vertical adjustment to accommodate subjects with different stem length

and/or stem height requirements.

11

The bicycle’s crank arm (Figure 3 below) is the lever for the transferring the
applied driving force from the feet to the back wheel. In this case the original crank arms

were utilized, and had a length of approximately 165mm from spindle to pedal, which

Figure 3: Cycle crank arm and pedal surface

Pedal Surface ‘

CrankArm/'B. , .
\ "xii. ' , ,_.I
was slightly shorter than the 170 mm optimal crank length suggested for maximum

   

power output (Martin and Spirduso 2001 ). However, Martin and Spirduso (2001) found
only a 4% difference in maximum power output across a crank length range of 120 — 220
mm in trained cyclists, which suggested our selection of crank arm length was adequate
for this investigation.

The electronic display of the Velodyne provided continuous feedback to the
subject, allowing him to maintain constant power output during cycling, independent of
pedaling frequency (cadence), speed, and gear ratio. This feature was used during all tests

so that each subject would maintain a constant power output of 125 watts, and created a

standard for qualitative and quantitative data comparisons both within and between
subjects.

In conjunction with the Velodyne, a cycling computer (Cateye® Astrale 8) was
ﬁtted to the experimental cycle and indicated the subject’s pedaling frequency (cadence)
with a small magnet placed on the left crank arm and a magnetic pickup on the frame that

sends a pulse to the cycling computer with each crank rotation.

Load Cells

To measure the forces present at the cycle/rider interfaces, ﬁve multi-axis force
transducers (or load cells) were integrated into the bicycle between the ﬂame and seat,
ﬂame and handlebars, and ﬂame and pedals. In our experimental arrangement all forces
and moments that resulted ﬂom the interaction between the subject and cycle acted
through the load cells. Both pedals were instrumented independent of the other and
similarly, as stated previously, the handlebars were modiﬁed and instrumented in such a
way as to decouple the left and right sides. Each load cell was used to measure forces in
three directions, F x, F y, and F2, as well as three moments Mx, My, and M2. Unlike the
measured forces, which are only dependant on the direction of force application, the
measured moments are dependant on the direction of applied force relative to a reference
point; in this case the center of the force plate.

The load cells were Advanced Mechanical Technologies, Inc. (AMTI) MC3A
series which were based on strain gage technology. Minimized gage cross talk between
channels and thermal stability, through the use of four-arm bridges, are built into each

load cell. Two 1,112 N (2501b) capacity load cells were located under the handlebar

l3

grips, and 4,450 N (10001b) capacity load cells were located under the seat and both
pedals.

The load cells were mated with AMTI ampliﬁers and set to a gain of 1000. Each
ampliﬁer had a built-in ﬁlter for noise reduction, and all were set to 10.5 Hz for each test.
A calibration ﬁle was incorporated for data acquisition and used the dominant diagonal
calibration values provided by AMTI for each channel in the load cells. Although the
load cells are precision instruments and their calibration values were factory measured,
the load cell calibrations were checked once before and once after testing all subjects to
assure validity. The pedal and handlebar load cells were removed ﬂom the bicycle, and
known weights were applied in the vertical measurement direction. Known weights
ranging ﬂom 1 1 IN to 445N (251bf to lOOlbt) were applied to the pedal load cells, and
weights ranging ﬂom 22N to 89N (Slbf to 201bf) were applied to the handlebar load cells.
Due to the difﬁculty in attachment of the load cell under the seat, it was not removed for
calibration. Instead, a board was placed across the top surface of the seat before known
weights ranging ﬂom 222 N to 556N (50 lbf to 125 lbf) were applied. It was expected
that the largest reaction forces would occur in the vertical direction to counteract the body
force, and all ﬁve force plates showed accurate and repeatable calibration measurements

for each of four known weight values both before and after testing.

Motion Capture

A Qualisys motion measurement system was utilized to track the positions of
retro-reﬂective targets placed at key landmarks on both the subject’s body and the
experimental cycle. Five motion cameras positioned around the test area collected

motion data at their maximum ﬂequency of 60 Hz. Clusters of inﬂa-red (IR) light

14

emitting diodes (LEDs) surrounded each camera lens. Each camera’s image sensor
detected the reﬂected IR light ﬂom the retro-reﬂective targets and returned two-
dimensional position data. Three-dimensional position data was calculated through
proprietary Qualisys software that required each retro-reﬂective target be seen at all times
by at least two cameras. The use of IR reﬂection allowed for testing to be conducted
under regular laboratory lighting conditions.

Retro-reﬂective targets were made ﬂom lightweight wooden spheres with a
diameter of approximately 20mm attached to a ﬂexible base similar to vinyl. The base
was oblong in shape to provide a suitable surface for taping to the subject’s skin. The
spheres were completely covered with 3MTM high gain 7610 industrial grade reﬂective
sheeting that provided 700-900 times more luminescence compared with light reﬂection
ﬂom a white screen, even when viewed ﬂom signiﬁcant angles. The fully coated,
spherical shape of the targets helped maximize visibility in the various positions attained
throughout testing.

The motion system was calibrated just prior to each subject’s test, even when
testing more than one subject per day. The calibration structure had four retro-reﬂective
reference targets at known, ﬁxed positions on a ﬂame, as well as a wand of known length
with retro-reﬂective targets at both ends. The static structure set the global coordinate
system of the test area, while movement of the wand in the test space provided a method
for calibrating a region of the lab larger than the frame itself. Together they provide a
length scale for the tracking system. Linearization ﬁles provided by the manufacturer for
each camera lens were loaded into the collection software prior to each calibration, as

were the length parameters for the calibration structure and wand.

15

Pressure System

A Tekscan Body Pressure Measurement SystemTM (BPMS) was used primarily as
a qualitative tool to determine where regions of contact occurred at the seat/rider
interface. The BPMS collects interface pressure information with a pressure mat, a thin
printed circuit encased in a ﬂexible plastic backing material (~20”x17”x0.012”). The
sensor (Tekscan Model #5315) was made up of 2,016 “sensels” arranged in a matrix of
48 columns and 42 rows across the mat. Each “sensel” varied resistance with a change in
the average load applied across its surface and can detect pressures within a range of O -
0.0345 N/mm2 (0-5 PSI) when properly calibrated.

Calibration of the BPMS required ﬁrst that each pressure mat be conditioned, a
process of repeatedly loading and unloading the mat with even pressure distribution.
Using a rubber bladder device developed by Tekscan, the entire sensing area of the mat
was loaded evenly to approximately 0.0172 N/mm2 (2.5 PSI) and held for 30 seconds.
The pressure was then released and the mat was allowed enough time to return to its
initial state of near zero before another load/unload sequence. Two mats were used
during this investigation and ten conditioning sequences were performed for each mat
prior to its use.

Aﬁer conditioned, the pressure mat was equilibrated under constant pressure of
approximately 0.0172 N/mm2 (2.5 PSI) over its entire surface using the previously
described air bladder system. Equilibration effectively zeroes the pressure acquisition
system across every “sensel” in the sensor’s matrix. The equilibration ﬁle was then

loaded into the computer software prior to calibration.

l6

Calibration of the pressure system allowed for either a one point linear calibration
(assuming a zero load after equilibration) or a non-linear calibration using two data points
at different load levels. Tekscan recommended a calibration load of at least 80% of the
maximum load expected to be seen for a one-point calibration. The pressure mat was
placed on a hard surface (plywood) and 334 N (75 lbf) of dead weight were used to
directly load the measurement area for the ﬁrst data point. The hard surface was chosen
to minimize any surface deformation of the mat due to the load placement. The
maximum pressure saturation value was noted and next a 445 N (100 lbf) load was
applied for the second data point and the maximum pressure saturation value was again
noted. Although the pressure mat system was used primarily for qualitative analysis, the
calibration ﬁle resulting in the highest saturation pressure resolution was used to increase
the accuracy in pressure measurements. With a weight diameter of approximately 267
mm (10.5 inches), the loaded area of the mat was approximately 56,200 mm2 (87 inz) and

covered the area that would be loaded during testing.

Subject Recruitment and Selection

Results ﬂom this research may be applicable to any person who rides a bicycle
and as such, subjects were initially recruited ﬂom the general population as well as ﬂom
the avid cycling community for a pilot study. Potential subjects were brought into the
laboratory and asked several questions pertaining to their cycling activities. Examples
included age, number of years of cycling experience, most ﬂequent type of cycling
activity, and if they had recently experienced any type of internal (i.e. knee or groin)
injury. Potential subjects under the age of 18, those who were pregnant, and those

reporting an injury were dismissed as participants for this study (those who reported an

17

injury were not included because of the possibility of data variability due to such an
injury).

After initial screening of potential subjects, the testing protocol was discussed
with each qualiﬁed subject. If agreeable, he or she was asked to sign an approved
consent form (MSU CRIRB #05-456) to be interviewed, tested, and photographed. Three
males and one female subject participated in the pilot study, and within the male group
one subject was an avid cyclist while the other two were not. The female subject was an
experienced cyclist.

Data acquired ﬂom pilot testing indicated ﬂuid movement patterns and smooth
force curves for the avid cyclists of both genders. Also, a recent investigation by Bressel
and Cronin (2004) showed signiﬁcant differences in seat pressures between males and
females in several different cycling positions. From these observations we decided to
include only avid or recreational male cyclists as subjects for this investigation, and
recruitment was done through the placement of ﬂiers at several local bicycle shops. In
total 12 male cyclists participated as test subjects for this research. Due to complications

that arose in data collection with two of the subjects, data ﬂom ten were used in this

 

 

 

 

 

 

 

 

 

 

 

analysis.
Table 1: Male Sub' ect Anthropometry
Subject Height Weight Activity
cm (in) kg (lbf) Miles/Week
0 172.7 (68) 65.8 (145) 200
1 177.8 (70L 72.1 (159) 100
3 173.4 (68.25) 71.9 (158.4) 50
4 180.3 (71) 80.3 (177) 225
6 181.6 (71.5) 71.5 (157.6) 150
7 185.4 (73) 74.8 (164.8) 220
8 185.4 (73) 77.7 (171.2) 70
9 175.3 (69) 72.1 (159) 135
10 175.3 (69) 69.4 (153L 60

 

 

 

 

18

 

 

 

 

 

 

 

 

 

 

 

11 181.6 (71.5) 82.2 (181.2) 100
Max 185.4 (73) 82.2 (181.2) 225
Min 172.7 (68) 65.8 (145) 50
Ave 178.9 (70.4) 73.76 (162.6) 131
Std. Dev. 4.695 (1.848) 5.0221 (11.07) 65.9
Testing
Subject Targeting

Prior to a subject’s arrival in the lab, gauze and alcohol swabs were readied to

clean the subject’s skin. The retro-reﬂective targets were laid out and a hypoallergenic,

breathable medical tape used for ﬁxation to the skin was applied to the target base. The

adhesion between the target and its backing material was also checked to ensure dynamic

stability of the target during testing.

Once the subject was familiarized with the investigation and signed the consent

form, he was asked to change into tight-ﬁtting attire, including cycling shorts, a shirt, and

athletic shoes. Clip-in style bicycle shoes and pedals were not used for this study. Nine

of the ten subjects chose not to wear a shirt to improve the placement of back and chest

targets directly on the skin. The subjects were then weighed without shoes or socks, and

a measure of body fat was taken using the bioelectrical impedance method with a

Tanita® TBF-551 Body Fat scale. The scale passes a very low electrical signal through

the body and the subject’s body fat percentage is returned based on impedance ﬁgures

ﬂom the manufacturer’s calibration.

The subject’s inseam length was measured at this time without his shoes or socks.

With his back to the wall, the subject was asked to hold a thick ruler ﬁrmly into his

crotch. A bubble level was used to level the ruler with the ﬂoor and the inseam length

was measured ﬂom the lab ﬂoor to the top of the ruler.

19

 

Next, the subject was seated and asked to put on his socks and athletic shoes to
begin target placement. Targets were afﬁxed bilaterally at various locations including
bony prominences near the ends of the limbs. Table 2 contains a listing of targeted
locations on the body. Anatomic locations of target placements can be seen in Figure 4

and Figure 5.

20

Table 2: Subject TargetingTable

 

Stemal Notch

 

Mid-sternum

 

C7 (Spinous Process of the Seventh Cervical Vertebra)

 

T7 ( Spinous Process of the Seventh Thoracic Vertebra)

 

L5 (Spinous process of the Fifth Lumbar Vertebra)

 

Right and left side of head at approximate center of gravity (approximately over the
inferior aspect of the joint between the sphenoid and temporal bones and 1 cm above
the mid-line of the Frankfort plane)

 

Forehead

 

Right and left acromion process (shoulder)

 

Right and left anterior superior iliac spine (ASIS)

 

Right and left head of greater trochanter (Hip)

 

Right and leﬁ mid-thigh

 

Right and left lateral condyle (knee)

 

Right and leﬁ mid-shank

 

Right and left lateral malleolus (ankle)

 

Right and leﬁ heel

 

Right and left tip of second toe

 

Right and left lateral humeral epicondyle (elbow)

 

 

Right and left radial epicondyle (wrist)

 

21

 

Figure 4: Anterior Target Locations
h ://members.aol.com/Attic21/Anatom /skeleton1.html (8/21/2006)

 

Forehead

Stemal Notch m

   
  
 
    
   

Mid Stemum

 

 

ASIS

 

 

 

Right and Left Head

Acromium Process

Lateral Epicondyle

A/Head of Greater

‘ Trochanter

 

Radial Epicondyle

(R‘s.
( 1“.
. ‘1‘

 

Lateral Malleolus

../

 

  

22

Figure 5: Posterior Target Locations

www.biorelax.hit/byposterior spineﬂ'f (8/22/06)

Spinous
process of C7

, Spinous
process of T7

Spinous
process of C5

 

 

23

Once fully targeted, several basic anthropometric measures were taken. Link
length measurements of the arms and legs were taken on all subjects along the right side
of the body. The distance between the right and leﬁ acromium process was measured to
determine the approximate width of the shoulders. The width, depth, and height of the
pelvis were also measured.

Additionally, two targets were permanently afﬁxed to the experimental cycle at

the left pedal spindle and the back of the left pedal, Figure 6 below. The spindle target

Figure 6: Left Pedal — Spindle and Back
....1.’.sdal.TargetS.

    

Back Pedal

Leﬁ Spindle Target

Target

.__. ~—-——-v—~ :“
4 u ‘

was used to ascribe a reference ﬂame for various events that occur during a single pedal
stroke (0°-360°). As the pedal load cells are ﬂee to rotate about their spindles, the left-
spindle and leﬁ-back pedal targets were used to assign a local coordinate system during
data reduction for transformation of the local leﬁ pedal forces into global (laboratory)

forces. There were no other targets placed on the cycling device.

Equipment Preparation

Calibration of the pressure and camera system was done before each subject’s

testing sequence began. The motion cameras, load cell ampliﬁers, and all computer

24

systems (pressure, force, motion, and Velodyne) were turned on at least 15 minutes
before calibration began to ensure that all components were properly warmed up.
Calibration of the pressure system was typically accomplished prior to the subject arrival
in the lab and was carried out according to the previous description in the Test Equipment
section.

Before calibrating the motion system the cycle device was unplugged and
removed ﬂom the testing area, and care was taken to either cover or remove all reﬂective
objects ﬂom the ﬁeld of view of any camera. The motion calibration sequence was run
twice according to the manufacturer’s instructions to assure similar calibration values,
and was captured at the maximum ﬂame rate for the cameras (60 Hz) for ten seconds.
The second calibration ﬁle was loaded into the motion capture soﬁware in preparation to
begin testing.

After motion calibration, the cycle device was reintroduced into the test space.
The load cell cables were reattached, and the pressure mat was placed on the seat surface.
Each load cell’s ampliﬁer channels were balanced with the seat and handlebar mounts in
place. The pedals were held such that the pedaling surface was parallel to the ground so
that the only force acting on the transducer was ﬂom the aluminum pedal surface. Also,
the handlebar mounts and seat surface were leveled with a bubble level to replicate their
position during testing. An initial force ﬁle was taken at 60 Hz for two seconds. Since
these initial force data values were already present before any testing began, they were
subtracted off of all force ﬁles during later data reduction. With the seat’s load cell in a
ﬁxed position relative to the seat surface (Figure 7), the correct “zeros” could be

subtracted prior to transformation ﬂom local force coordinates into lab coordinates.

25

Figure 7: Cycle Seat and Load cell

 

26

Initial Device Setup

The cycling device’s seat height was initially set according to each subject’s seat
height on their own bicycle, and was measured from the center of the crank arm spindle

to the top of the seat surface directly above the center of the load cell. Small adjustments

Figure 8: Cycle Seat Height Adjustment

 

 

 

 

 

were made as requested to accommodate for small differences between the height of the
pedaling surface and spindle on the device as compared to the subject’s own bicycle
pedals. The handlebar tops were then set approximately level with the seat surface, and
the length ﬂom the seat to the handlebars was also adjusted to that of their own bicycle.
Setting the handlebar tops level with the seat is a recommended starting point for cycling
comfort (Mellion 1996), and is common in retail bicycle stores for initial ﬁt adjustments

on new bike purchases.

27

Test Descriptions

Measure of Ischial Tuberosities

A static pressure ﬁle was collected to approximate the width of the ischial
tuberosities (lTs), or sit bones, as this is a difﬁcult and sensitive area to accurately
measure with an anthropometer. The stiff wooden platform used during pressure
calibration and the calibrated pressure mats were left in the test area just prior to motion
calibration. The subject was asked to sit on the mat with their back perpendicular to the
platform, feet ﬂat on the ﬂoor, and forearms resting along the knees. In this upright
seated position it was relatively easy to discern the two highest areas of pressure
concentration and estimate the location of the ITs. The subject was asked to hold this
position and a pressure ﬁle was collected for ﬁve seconds at 60 Hz. No force or motion
data were collected concurrently with this test.

The pressure mat was replaced onto the top of the seat, and the wooden platform
was used to aid the subject in mounting the cycling device. The platform was

subsequently removed before all other testing.

Cycling Tests

With the seat height adjusted according to the subjects own bicycle (see
description of Initial Device Setup), the subject was asked to place his hands in the drop
section of the handlebars and indicate if a handlebar adjustment was required in the fore
and aft direction to obscure the axle of the Velodyne that clamped the ﬂont forks of the
cycle. Reach adjustments and checks were continued until the subject indicated he could

no longer see the ﬂont fork clamp in their line of sight through the top portion of the

28

handlebar. This was considered the Regular position and was the starting point for
testing.

The subject began to pedal the cycle and warmed up in the Regular position for
approximately 10 minutes with the external power output controlled at 100 watts, and a
subject regulated pedaling ﬂequency of 72-78 rotations per minute (RPM) via feedback
provided by the cycling computer. This warm-up period allowed the subject to become
familiar with the cycle set up, and gave them a feel for the desired pedaling ﬂequency for
each test.

After the warm-up period the external power output was increased on the
Velodyne to the desired testing value of 125 watts. The subject was then asked to
maintain a constant pedal ﬂequency in the range of 72-78 RPM, with a desired ﬂequency
of 75 RPM. After an adaptation period of two minutes at the new workload, ﬁve seconds
of motion, force, and pressure data was collected simultaneously at 60 Hz. Over the next
one and a half minutes, two additional ﬁve second trials were collected.

For the next set of tests, the subject was asked to stop pedaling and move the right
pedal and crank arm to the forward horizontal position. His foot was positioned such that
the ﬁrst metatarsal of the big toe lined up vertically over the spindle of the pedal and
using a commercially available bicycle foot strap was strapped down to the pedal surface.
The subject then rotated the left crank arm forward and the process was repeated for the
leﬁ foot.

The subject was asked to begin pedaling again, and the power was increased to

the desired 125 watts. Once the subject reached the desired steady state pedaling

29

ﬂequency (~75 RPM), he was given a two-minute adaptation period and three sets of
data were collected exactly as described above.

After accomplishing all pedaling tests in the Regular handlebar position, the
power output was incremented down to 0 watts as the subject stopped pedaling. The
handlebars were then moved closer to the seat by approximately 5 cm, deﬁned as the
Close position. The distance of 5 cm was chosen as it was expected that this would be on
the extreme short end of the range of stem lengths commercially available for purchase.
The testing procedure was repeated almost exactly as described for the Regular position,
with the only exception being the sequence of strapping the feet to the pedals. At the end
of the Regular position testing, the subject’s feet were left strapped onto the pedals.
These three sets of strapped data were collected ﬁrst in the Close position. The subject’s
feet were then un-strapped, and again three sets of data collected.

Once all tests were complete in the Close handlebar position, the subject was
asked to stop pedaling and the power output was incremented down to zero. The
handlebars were then moved 10 cm forward of the Close handlebar position, or 5 cm
forward of the initial Regular handlebar position, to the Far handlebar position. The
distance of 5 cm forward of Regular was chosen to approximate the extreme far end of
commercially available stem lengths that a person may select for personal use. Once
adjusted to the Far position, testing was carried out exactly as described previously for
the Regular position, as this time the subject’s feet were un-strapped in the last test of the

Close position.

30

Analysis

The laboratory coordinate system was deﬁned during motion calibration with the
+y-axis directed towards the front of the cycle, the +z-axis directed away ﬂom the lab
ﬂoor, and the +x-axis directed to the right and away ﬂom the cycle, Figure 9. This

Figure 9: Laboratory (Global) Coordinate System;
+x Axis Pointed Into Paper

+2

I + y I ‘/ CYCIC

.. W I’

orientation was chosen to minimize the number of necessary coordinate transformations

 

 

 

 

of the load cell data.

To assure that the load cell cables did not interfere with normal pedaling of the
cycle, originally the load cells axes did not necessarily coincide with each other, or with
the laboratory coordinate system. For example, the left handlebar and left pedal load
cells were oriented with their cables exiting to the left of the cycle, while the right
handlebar and pedal were oriented with their cables exiting the load cell to the right of the

cycle.

31

It was desirable to describe all of the measured force data in the same coordinate
system as the motion data, which necessitated coordinate transformations at all of the

load cells. As an example, to arrive at the X’ and Y’ axes as shown in Figure 10, the

Figure 10: Example of a Coordinate System
Transformation from Unprimed to Primed Coordinates

Y,

Load Cell

 

Load Cell Cable

forces measured in the X and Y directions of this load cell coordinate system were
rotated by an angle of 0 = 90° about the Z-axis through the transformation matrix shown
in Equation 1. The coordinate transformations were automated with a computer

algorithm. This algorithm also subtracted any initial force data (zero ﬁle) ﬂom the raw

Equation 1: Transformation from unprimed to
primed coordinate system; 0 = 90°

FX' c030 sing 0 FX
FY‘ = -sin6 c086 0 FY
FZ‘ 0 0 l FZ
force data of each trial, performed the appropriate coordinate transformations

corresponding to an individual load cells orientation, and output the corrected force data
into a spreadsheet ﬁle. During pilot testing, several transformed values were checked via

hand calculations to verify that the computer program worked properly.

32

Equation 2: Calculation of the pedal surface unit vector as
the original vector divided by its magnitude

mi
IVI

A single coordinate transformation was adequate to attain force data ﬂom the
handlebars and seat load cells that coincided with the motion data in the laboratory
coordinates. However, the pedal load cells were unique, as they also rotated about their

X’-axes while pedaling, Figure 11. Thus, an additional transformation was needed to

Figure 11: Vector Describing the Left Pedal’s
Surface Orientation that was Used to Rotate the
Left Pedal Forces into the Laboratory
Coordinates; X’-axis into the paper

Z’ Pedal

  

 

\ Load Cell

Spindle target
fully describe the pedal forces in terms of the laboratory coordinate system. This was
done after motion data was imported into the corrected force data spreadsheet ﬁle.
Recalled from the Methods section, the left pedal was targeted to ﬁnd a vector
parallel to the orientation of the pedal surface. This vector described the position of the
pedal spindle target relative to the rearward pedal target (V in Figure 11) and was used to
deﬁne the angular orientation of the pedal surface (Y’-axis) in the laboratory y-z plane.

As V was described in laboratory y and z coordinates directly ﬂom the motion data, a

unit vector (magnitude equal tol) I; was calculated parallel to V.

33

Next, the laboratory y-axis was assigned a unit vector 52 , and the angle 0 was

calculated as the arccosine of the component of the unit vector 1; in the direction of j» ,
Equation 3. An orthogonal Z’-axis was subsequently deﬁned normal to and directed

Equation 3: Calculation of the pedal surface angle relative to the laboratory
coordinate system; V(y) was the y-component of the unit vector V

0 = arccos (V(y))

away ﬂom the pedal surface (see Figure 11). Finally, the force data ﬂom the left pedal’s

load cell was transformed into the laboratory coordinate system according to Equation 4.
The motion data ﬂom the left pedal spindle target was also used to ascribe a

radial vector coinciding with the longitudinal neutral axis of the crank arm (Figure 12).

As the crank arm rotated in the y-z plane, the maximum and minimum y and 2 positions

Equation 4: Additional pedal force
transformation into laboratory coordinates

Fx 1 0 0 FX'
Fy = 0 c080 sin0 FY'
F2 0 —sin6 c039 FZ'

for the pedal spindle were found. These respective minimum and maximum values were
averaged to obtain the y-z position for the center of crank arm rotation. A position vector
was then calculated in laboratory y-z components ﬂom the calculated center of the crank
arm rotation to the pedal spindle target describing the radial direction (r, Figure 12) of the
crank arm. The crank arm angle 9 was found using a similar procedure to that described
for the pedal surface angle represented bye. The left crank arm angle was deﬁned as 0°

when it coincided with the laboratory z-axis, and subsequent crank arm angles were

34

positive in a counterclockwise movement as viewed ﬂom the left hand side of the cycle

as seen in Figure 12.

Figure 12: Deﬁnition of the Radial and Tangent Crank Arm Directions, as well
as the Crank Arm Angle as Viewed from the Left Side of the Cycle

Pedal Spindle ’2

Center of Crank
Arm Rotation

 

The difference between the left pedal surface angle (0) and crank arm angle (4))
was used to develop the force component used to drive the crank arm through a
revolution; that which was tangent to the crank arm path. The tangent force component
has been studied previously by other authors, and it was also calculated in this work as to
allow comparisons with reported literature. 1

In each handlebar position (Close, Regular, and Far as described in the Methods
section), two of the three trials were analyzed. The two trials were selected based on
their completeness of force, motion, and pressure data. The force and motion data were
cyclical in nature, and the maximum and minimum force values for each of ﬁve
complete, continuous crank arm revolutions per trial were evaluated. The maximum and
minimum forces were chosen since they represented the extreme force values that must
be resisted somewhere within the subject’s body. This method was previously used by

Stone and Hull (1995) to determine if interface force values were correlated with a

35

subject’s weight. Here, the maximum and minimum force values were also calculated as
a percentage of the subject’s body weight (% BW). Additionally, the left crank arm
angles at which the maximum and minimum interface forces occurred were also retrieved
ﬂom the motion data and deﬁned as “timing angles.” Mean (average) and standard
deviation (SD) values of the ten maximum forces, ten minimum forces, forces in % BW,
and ten timing angles for each handlebar position were then calculated and analyzed to
arrive at a grand mean for all of the subjects tested.

Finally, it was hypothesized that a change in the reach, deﬁned by the distance
between the seat and the handlebars (i.e. Close, Regular, and Far), would not signiﬁcantly
affect the magnitudes of the forces present at each of the rider/cycle interfaces. Thus, a
statistical analysis was done using the Mixed Procedure in SAS v9.1, which compared
the mean maximum forces, minimum forces, and timing angles across the subjects in all
three handlebar positions. With the conﬁdence level set at 95%, signiﬁcant differences in

the force and timing angle values were present for P values less than 0.05.

36

Results

The quantiﬁed values presented in the tables and ﬁgures in this section were
measured with all subjects set up in the Regular handlebar position, described previously
in the section titled Research Methods. Due to the quantity of data collected, data ﬂom
the Close and Far handlebar bar positions were used for statistical comparisons. Due to
problems with data collection and storage, signiﬁcant data loss occurred for subjects 2
and 5. Therefore, analyses for these subjects were not conducted.

Although the test protocol involved data collection both with and without the
subject’s feet strapped to pedals, only an analysis of the feet strapped to the pedals was
presented here. During the early phases of data collection, several subjects voiced
concern that their feet were slipping on the pedal surface when they were not strapped to
the pedal, which made it more difﬁcult to maintain a consistent and smooth pedaling
cadence. Having the subject’s feet strapped to the pedals also more accurately
represented the realistic bicycling situation, as the trend for recreational and avid
bicyclists is to have their shoes mechanically coupled to the pedal with either foot straps,
or clip-in style pedals similar to ski bindings.

Force data collected ﬂom the pedals, seat, and both the left and right handlebars
will be presented, as well as pressure mapping data collected ﬂom the seat. Mean
(averaged) values of the maximum and minimum forces were computed over ten
complete revolutions of the left crank arm, with the standard deviation (SD) included in
parentheses. The force values were also calculated as a percentage of the subject’s body
weight and are included in tabular form. The pedal forces have been rigorously studied

by other authors and were not the main focus of this investigation. Therefore, not all of

37

the pedal forces were analyzed, and those presented in this work were included to make
comparisons with previous investigations.

To develop an understanding of when the maximum and minimum forces
occurred during the pedal stroke, left crank arm angles corresponding to a maximum or
minimum force were deﬁned as a “timing angle.” All timing angles were deﬁned with 0°
as the highest point of the left crank arm during a pedal revolution, and positive angles
measured in a counterclockwise fashion as viewed ﬂom the left side of the cycle.

Finally, the results of a statistical analysis that described the effects of changing
the reach to the handlebars on the forces will be presented. The statistical analysis was
done for all of the presented values, but only those that indicated a signiﬁcant difference
existed in the force values for the different handlebar positions were included here. The
quantiﬁcation of statistical signiﬁcance was reported for values of P < 0.15 with a

conﬁdence level set at 95%.

38

Pedal and Crank Tangent Forces

Force data was collected at both the left and right pedals. However, only the left
pedal was targeted and the local pedal coordinate system was deﬁned to calculate the
relative angle between the pedal surface and thecrank arm. The pedal forces were then
transformed and gave a force vector with components described as parallel and
perpendicular to the crank arm.

Work was done on the crank arm, and hence power delivered to drive the rear
wheel of the cycle device, through the pedal force component perpendicular to the crank

arm, Figure 13.

Figure 13: Work and Power Done
by Pedal Forces

 

As a reminder, work done by forces on the pedal was the product of an applied
force and the distance over which that force acts.
Work = Force x Distance
Power was then the total amount of work done over a period of time.

Power = Work / Time

39

In the case of the cycle, instantaneous power was the product of the force
component tangent to the path of the crank arm (Figure 14) and the tangent component of

the left pedal spindle velocity vector. These quantities were available through the load

cell and motion data.

Figure 14: Proﬁle of the Left Pedal Force Tangent to the Crank Arm Path; Single
trial, single subject

Degrees

240

 

om-s
O

m...
0

m4
0

00‘

a)

160 n A

..l /\ /\ ll 1/
M M

Shown in Figure 15 below, the left pedal force component tangent to the crank

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Force (N)

 

 

 

 

arm path was positive in the region ﬂom 0-180°, provided positive work about the center

Figure 15: Positive and Negative Work on Pedal

Poettlve 9°

Tangent
Component
180
Negaﬂve
Tangent
Component

40

of the crank arm’s path, and contributed positive power to drive the left crank arm. In the
region approximated by l80-360° the force component of the left pedal was negative, and
contributed work against the rotation of the crank arms. From this observation, the left
leg was considered to be “driving” when its angular position moved through 0-180° and
“non-driving” when its angular position moved through l80-360°. In the negative
region, a portion of the positive work and power provided by the driving leg was used to
overcome the negative work from the force applied through the non-driving leg.

Although force data was collected ﬂom the right pedal, a measure of the tangent
force was not possible. Since the right pedal was not targeted no local coordinate system
could be deﬁned. It was assumed that the right pedal displayed a similar tangent force
proﬁle to that of the left pedal, and therefore the right leg was considered as “non-
driving” during 0-180° and “driving” during 180-360° of the crank arm revolution.

For the left pedal, the maximum and minimum pedal force component tangent to
the crank arm path varied across the subjects even with the average power output
maintained at 125 watts for all tests. In the Regular position, the average maximum force
values ranged ﬂom 143N (1 IN) for Subject 4 to 212N (8N) for Subject 11, with a grand
mean of 173N (24N) across all of the subjects. The average minimum force ranged ﬂom
-59N (6) to 103N (4N), with a grand mean of -84N (16N). The negative values
associated with the minimum pedal force values indicated the forces were directed

opposite to the rotation of the crank arm and pedal spindle.

41

Table 3: Average Pedal Force Component Tangent to Crank Arm Path

 

 

 

 

 

 

 

 

 

 

 

 

Maximum Force (SD) Minimum Force (SD)
Subject Newtons Newtons
0 186 (5) -64 (4)
1 1 67 (22) -96 (1 3)
3 162 (15) -59 (6)
4 143(11) -93 (13)
6 167 (14) -77 (7)
7 1 86 (20) -89 (9)
8 148 (18) -77 (6)
9 168 (16) -94 (7)
10 188 (18) -89 (5)
11 212 (a) -103 (4)
Grand Mean 173 (24) -84 (16)

 

 

 

 

 

42

Presented in Table 4 below, the timing angle of the maximum force component
tangent to the crank arm path ranged ﬂom 81° (4°) to 119° (8°), with a grand mean of
104° (13°). The timing angle of the minimum tangent force ranged from 271° (33°) to
289° (8°), with a grand mean of 281° (14°) across all subjects.

Table 4: Angle at which the Applied Maximum and Minimum Force Component
Tangent to the Left Crank Arm Path Occurred (Timing Angle)

 

 

 

 

 

 

 

 

 

 

 

 

Subject Maximum Force Angle Minimum Force Angle
Degees (SD) Degrees (SD)
0 103 (8) 287 (10)
1 97 (8) 289(8)
3 105 (14) 283(6)
4 100(9) 287 (11)
5 109(7) 285(8)
7 81 (4) 271 (33)
3 119(8) 288(5)
9 107 (3) 271 (4)
‘0 117 (5) 281 (6)
‘1 105 (5) 273 (13)
Grand Mean 104 (13) 281 (14)

 

 

 

 

 

43

The lateral, or side to side pedal forces were measured at both the right and left
pedal. This force component was independent of the pedal surface angle in the plane of
the cycle, unlike the pedal force component tangent to the crank arm path mentioned
above. It should ﬁrst be noted that in the laboratory coordinate system, a positive force
value is directed away ﬂom the cycle as measured at the right pedal, as is a negative force
value at the left pedal. The magnitude of the right pedal lateral force (Table 5) ranged
ﬂom 33N (ION) to 52N (2N) with a grand mean of 41N (7N) at the right pedal, and -26N
(3) to -54N (2) with a grand mean of -38N (10) at the left pedal.

Table 5: Lateral (side to side) Right and Left Pedal Maximum Forces;
Forces directed away from cycle were positive on the right and negative on the left

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Right Pedal Left Pedal
Subject Maximum Force (SD) Maximum Force (SD)
Newtons Newtons
0 48(2) -54 (2)
1 33 (10) -34 (12)
3 38 (3) -50 (5)
4 36 (3) -26 (3)
6 37(3) -30 (3)
7 42 (6) -41 (7)
8 38 (3) -3O (6)
9 43(6) -39 (3)
1 0 45 (5) -40 (5)
11 52 (2) -39 (1)
Grand Mean 41 (7) ~38 (10)

 

44

 

The timing angle associated with the right maximum lateral pedal forces (Table 6)
ranged from 278° (16°) to 334° (20°), with a grand mean of 299° (17°). The timing angle
associated with the maximum lateral left pedal force ranged ﬂom 96° (33°) to 131° (4°),
with a grand mean of 116° (16°).

Table 6: Timing Angle of Maximum Lateral Pedal Force

 

 

 

 

 

 

 

 

 

 

 

 

 

Right Left

Subject Timing Angle Timing Angle
Dimes (SD) Degrees (SD)

0 288(5) 104(6)

1 334(20) 96(33)

3 293(7) 121(13)

4 303 (5) 1 1 6 (8)

6 278(16) 117(5)

7 302 (8) 1 05 (8)

8 305(7) 119(11)

9 mun 1mm

10 297(5) 128 (10)

11 303(5) 131(4)

Grand Mean 299 (17) 116 (16)

 

 

 

 

 

45

The minimum lateral forces at the pedals were directed towards the cycle, as
indicated by the negative value (Table 7) on the right pedal and the positive value on the
left pedal. The minimum lateral force measured at the surface of the right pedal ranged
ﬂom ON (IN) to -10N (5N), with a grand meanof -5N (4N) across all subjects. The
minimum lateral force measured at the surface of the left pedal ranged from 0N (1N) to
16N (2N), with a grand mean of 7N (4N).

Table 7: Minimum Right and Left Pedal Lateral Forces;

Forces directed towards the cycle were
negative on the right pedal and positive on the left

 

 

 

 

 

 

 

 

 

 

 

 

Right Pedal Left Pedal
Subject Minimum Force (SD) Minimum Force (SD)
Newtons Newtons
0 -5 (1) 0(1)
1 -2 (6) 6(3)
3 -3 (1) 8 (3)
4 -5 (3) 8(2)
6 -10 (5) 5 (2)
7 o (1) 3(2)
8 -6 (3) 10(3)
9 -6 (1) 7(1)
1o -8 (4) 16 (2)
11 -5 (1) 9(1)
Grand Mean -5 (4) 7(4)

 

 

 

 

 

46

The timing angles of the minimum lateral pedal forces were approximately 113°
(38°) for the right pedal and 275° (48°) for the left pedal. There was more variability, as
represented by the larger standard deviations, in the timing angle of the minimum lateral
pedal forces than the maximum lateral pedal forces.

Table 8: Timing Angle of Minimum Lateral Pedal Forces

 

 

 

 

 

 

 

 

 

 

 

 

Right Left

Subject Timing Angle Timing Angle
Degrees (SQ Degees (SD)

0 117 (32) 254 (47)

1 125 (44) 326 (25)

3 127 (18) 241 (17)

4 94 (27) 272 (41)

6 98 (49) 280 (97)

7 89 (1 3) 279 (5)

8 1 03 (20) 232 (24)

9 105(11) 311(8)

10 1 14 (58) 245 (4)

1 1 1 56 (36) 313 (4)

Grand Mean 1 13 (38) 275 (48)

 

 

 

 

 

47

The range between the minimum and maximum lateral force of the right lateral
pedal forces varied ﬂom 36N (14N) to 56N (4N) with a grand mean of 46N (9N) across
all subjects. For the left pedal, the range varied ﬂom 35N (4N) to 58N (6N) with a grand

mean of 45N (10N).

Table 9: Range between Maximum and Minimum Lateral Pedal Forces

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Pedal Left Pedal
Newtons 18D) Newtons (SD)
0 53(2) 54(3)
1 36 (14) 41 (13)
3 41 (3) 58(6)
4 41 (4) 34 (4)
6 47 (5) 35 (4)
7 42 (6) 43(8)
8 44 (4) 40 (6)
9 49(5) 46 (3)
10 53 (7) 55 (6)
11 56 (4) 48 (2)
Grand Mean 46(9) 45 (10)

 

48

 

 

Seat Vertical Forces

Shown in Figure 16 is representative data of the vertical seat force over ﬁve crank

arm revolutions gathered ﬂom a single trial of one subject. The vertical force at the seat

Figure 16: Vertical Seat Force Profile over Five Crank Arm Revolutions;

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Single subject
Degrees
-1 90
0 1 0 1 0 1 0 1 0 1
8 8 8 8 8
0 0 0 0 0
2
3 -245
E
-300

 

 

 

 

 

 

 

 

 

 

 

 

exhibited a “double cycle” force proﬁle per revolution of the crank arm.

The magnitude of the maximum vertical seat forces for all ten subjects ranged
ﬂom 285N (7N) to 472N (12N), with a grand mean of 372N (56N) during 0-180° and
369N (48N) during l80-360° of the crank arm revolution. In terms of percentage body
weight, while the left leg was driving the maximum vertical load on the seat averaged
across the subjects was 52% (6%) of the subject’s body weight (% BW), and 51% (5%)
BW while the right leg was driving. The maximum vertical seat force always acted
downward on the cycle, or upward on the rider’s groin. The maximum vertical seat force

values for all subjects are shown in Table 10.

49

Table 10: Maximum Seat Vertical Force and Standard Deviation (SD)

for the Regular Position;
Mative values indicate a force directed towards the gound

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

S . F 04800 Percent 1:80-3:01; Percent
“We“ 13:51.83) Body Weight 133:2“) Body Weight

0 -285 (7) 45% (1 %) -291 (6) 46% (1 %)

1 -393 (9) 56°/o (1 °/o) '343 (18) 49°/o (3%)

3 -310 (10) 44% (1 %) -325 (8) 47% (1%)

4 «172 (12) 61% (2%) -456 (7) 59% (1 %)

6 -362 (13) 52% (2%) -350 (13) 50% (2%)

7 -396(19) 55% (3%) -381 (16) 53% (2%)

8 -438 (22) 58 (3%) 413 (7) 55% (1 %)

9 -326 (7) 47% (1 %) -333 (11) 48% (2%)

10 -361 (14) 54% (2%) -371 (12) 55% (2%)

11 -374 (10) 47% (1 %) -373 (6) 47% (1 %)
Grand Mean -372 (56) 52% (6%) -364 (46) 51% (4%)

 

 

Table 11: Timing Angles at which the Maximum Vertical Seat Forces Occurred

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0-180° ISO-360°
Subject Angle°(SD) Angle°(SD)
0 72(8) 234(4)
1 157 (12) 292 (33)
3 85 (30) 301 (12)
4 1 09 (6) 280 (28)
6 120 (19) 315 (30)
7 1 32 (5) 31 7 (6)
8 173(7) 343(5)
9 77 (34) 324 (30)
1o 80 (22) 216 (9)
11 81 (11) 262 (41)
Grand Mean 108 (38) 288 (45)

 

 

 

 

Due to the variation seen in the timing angles for the maximum seat vertical force

(SD where about 20-25% of their respective regions of the crank arm revolution), another

50

method was attempted to describe this timing angle. However, a plot that described the
number of occurrences for the timing angle at the maximum vertical seat force, Figure

17, also showed no clear region in the crank arm revolution where the maximum vertical

seat forces occurred.

Figure 17: Maximum Vertical Seat Force Timing Angle Histogram

8

 

NOD
OO

 

Frequency

—L
o

 

O

0 180 360
Angle

51

The magnitude of the minimum vertical seat forces ranged ﬂom 202N (12N) to
382N (1 IN), and again acted in the downward direction on the cycle. Across all subjects,
the grand mean was 292N (49N) for 0-180° and 291N (44N) for 180-360°. After
normalized with respect to body weight, the grand mean of the minimum vertical seat
forces of all the subjects was 41% (6%) BW during 0-180° and 41% (5%) BW during
180-360° of the crank arm revolution.

Table 12: Minimum Seat Vertical Force and Standard Deviation (SD)

for the Regular position;
Negative values indicated a force directed downward

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. 0-1800 Percent 180.3600 Percent
sum“ was“? Body Weight $333) Body Weight

0 -202 (12) 32% (2%) -222 (13) 35% (2%)

1 -293 (10) 42% (2%) -298 (17) 43% (3%)

3 -251 (15) 36% (2%) -253 (19) 36% (3%)

4 -377 (12) 48% (2%) -382 (11) 49% (1 %)

6 -319 (17) 46% (2%) -302 (7) 44% (1 %)

7 -275 (17) 38% (2%) -276 (10) 38% (1 %)

8 -350 (16) 47% (2%) -335 (21) 44% (3%)

9 -283 (12) 40% (2%) -278 (10) 40% (1 %)

10 -286 (15) 43% (2%) -290 (8) 43% (1 %)

1 1 -279 (1 1) 35% (1 °/o) -279 (11) 35% (1 °/o)
Grand Mean -292 (49) 41 °/o (6%) -291 (44) 41% (5%)

 

52

 

 

The timing angles of the minimum seat vertical forces were 73° (75°) while the
left leg was driving and 243° (82°) while the right leg was driving. As can be seen in
Table 13, the standard deviations of the timing angle were greater than half of the range
they were measured over in some subjects, for example 111° in Subject 7.

Table 13: Timing Angle of Minimum Seat Vertical Forces

 

 

 

 

 

 

 

 

 

 

 

 

Subject 0-180° ISO-360°
Angl:(SD)° Ange (SD)
0 13(6) 254 (87)
1 78 (42) 288 (55)
3 139 (64) 186(3)
4 63 (78) 239 (82)
6 3O (29) 255 (59)
7 43 (111) 321 (73)
8 34(4) 223 (3)
9 53 (64) 201 (28)
10 111 (73) 288 (117)
11 161 (54) 169 (100)
Grand Mean 73 (75) 243 (82)

 

 

 

 

 

53

Similar to the timing angles of the maximum vertical seat forces, the grand mean
timing angles for the minimum vertical seat forces were difﬁcult to interpret, with the
standard deviations of 75° and 82° during 0-180° and 180—360°, respectively. Another
method of analysis provided a more informative description of the timing angles. This
was done with a histogram, Figure 18, which described the ﬂequency of occurrence for
the timing angles at the minimum vertical seat forces. It was observed that the minimum

vertical seat forces occurred at a much higher ﬂequencies over the ranges of 170°-230°

Figure 18: Minimum Seat Vertical Force Timing Angle Frequency

(D
O

 

Frequency
dNODBUIOJN
O O O O O O o

l

 

 

O

O 1 80 360
Crank Angle

(3 5% of values) and also ﬂom 350°-40° (38% of the values). Together these regions
contained a total of 73% of the timing angles at the minimum seat vertical force.

The range between the maximum and minimum vertical seat forces was then
calculated to reveal the difference in magnitude between them. The range of the vertical

seat force varied ﬂom 43N (12N) to 121N (14N) during 0—180° and 45N (17N) to 105N

54

(12N) during 180—360°. Across all subjects the grand mean difference between the

maximum and minimum mean seat vertical force was 80N (28N) for 0-180° and 72N

(24N) for l80-360°. In terms of percent body weight, the differences in the vertical seat

forces were approximately 11% (4%) for 0-180° and 10% (3%) for 180-360°. It should

again be noted that the vertical seat forces were always directed downward on the cycle.

Table 14: Range between the Maximum and Minimum Vertical Seat Forces

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0-180° ISO-360° P
Vertical Percent Vertical ercent
Subject Body Weight Body Weight
Force Range (SD) Force Range (SD)
Newtons (SD) Newtons (SD)
0 83 (16) 1 3% (3%) 69 (1 7) 1 1% (3%)
1 99 (13) 14% (2%) 45 (17) 6 (2%)
3 58 (20) 8% (3%) 72 (23) 1 0 (3%)
4 95 (7) 12% (1%) 74(8) 10 (0%)
6 43 (16) 6% (2%) 47 (16) 7 (2%)
7 121 (14) 17% (2%) 105 (12) 15 (2%)
8 87 (21) 12% (3%) 78 (23) 1o (3%)
9 43 (1 2) 6% (2%) 55 (1 6) 8 (2%)
10 75 (13) 1 1% (2%) 80 (1 1 ) 12 (2%)
11 95 (18) 12% (2%) 94 (11) 12 (1%)
Grand
Mean 80 (28) 11% (4%) 72 (24) 10% (3%)

 

55

 

 

Forward/RearWard Seat Forces

A representative forward/rearward (FR), seat force proﬁle for ﬁve full crank arm

revolutions of a single subject is shown in Figure 19.

Figure 19: Forward/Rearward (FR) Seat Force Profile over Five Subsequent Crank
Arm Revolutions; Single trial for one subject

Degrees

 

a:
Dad

Force (N)
8

 

 

-70 i . , l . . i . 7 . . 1

 

 

 

 

 

56

Across all 10 subjects, the maximum magnitude of the FR seat force in the Regular
position ranged from 41N (12N) to 1 UN (6N), with a grand mean of 78N (20N) that
occurred while the left leg was driving (0-180°) and 79N (22N) while the right leg was
driving (180-360°). The maximum FR force as a percentage of body weight across all
subjects was 11% (3%) while the left leg was driving and 11% (3%) while the right leg
was driving. As indicated by the negative values presented in Table 15, the maximum
magnitude of the FR seat force was always directed in the rearward direction on the
cycle.

Table 15: Maximum F orward/Rearward (FR) Seat Force
Negative Values Indicate a Force Directed Towards the Rear of the Cycle

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0-180° Percent 180-360° Percent
Subject Force(SD) Body Force(SD) Body
Newtons Weight Newtons Weight
0 -75 (5) 12% (1 %) -75 (3) 12% (1 %)
1 -55 (11) 8% (2%) -47 (19) 7% (3%)
3 -70 (6) 1o (1%) -81 (8) 12% (1%)
4 -84 (9) 11% (1 %) -81 (5) 10% (1%)
6 -41 (12) 5% (2%) -45 (11) 7% (2%)
7 -96 (3) 13% (0%) -93 (5) 13% (1 %)
8 -88 (9) 11% (1%) -82 (8) 11% (1%)
9 -102 (5) 15% (1 %) -111 (6) 16°/o (1 %)
10 -72 (9) 11% (1%) -65 (15) 10% (1%)
1 1 -96 (5) 12% (1 %) -107 (5) 13% (1 %)
Grand Mean -78 (20) 1 1% (3%) -79 (22) 1 1% (3%)

 

 

 

 

 

57

 

 

The timing angle of the maximum FR shear force occurred across all subjects at
approximately 81° (22°) while the left leg was driving and 267° (25°) while the right leg
was driving. Some of the variability may have been due to the ﬂequency at which
motion data was sampled (60Hz). With the subject’s maintaining a crank arm frequency
of 75 RPM, one ﬂames difference was approximately equal to 75° of crank arm rotation.
The phase difference between the driving regions was slightly greater than 180° albeit
with similar variability, and the difference may be explained by a subject that favored a
dominant leg (Smak et al. 1999), or some other musculoskeletal asymmetry in the
subject.

Table 16: Maximum Forward/Rearward Seat Force Timing Angles

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0—180° ISO-360°
Subject Agle(SD)° Angle(SD)
0 69 (11) 260 (14)
1 88 (17) 286 (13)
3 68 (19) 249(9)
4 106 (11) 293 (10)
6 87 (29) 274 (17)
7 73(8) 270(6)
8 94 (23) 256 (20)
9 69 (30) 277 (46)
10 65 (14) 259 (31)
11 90(5) 251 (6)
Grand Mean 81 (22) 268 (25)

 

 

The minimum FR seat shear, Table 17, ranged ﬂom ON (1 1N) to 85N (4N) with a
grand mean of 39N (22N) during 0-180°of a crank arm revolution, and 39N (22N) during
180-360°. In terms of percent body weight (%BW), the minimum mean FR seat shear is

approximately 5% BW (3%) during 0-180° and 6% BW (3%) during 180-360°. Similar

58

to the maximum mean FR seat shear, the minimum mean FR seat shear was always
directed in the rearward direction as indicated by the negative sign for the force values.

Table 17: Minimum FR Seat Shear Forces;
Negative values indicated that the forces were directed towards the rear of the cycle

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0-180° A 180-360°
Force(SD) Percent Force(SD) Percent
Subject Newtons Body Weight Newtons Body Weight

0 -43 (5) 7% (1 %) -42 (4) 7% (1 %)

1 -6 (1 3) 1 % (1 %) -O (1 1 ) 0% (2%)

3 -47 (4) 7% (1 %) -46 (4) 7% (1 %)

4 40 (5) 5% (1%) -45 (5) 6% (1%)

6 -13 (12) 2% (2%) -12 (12) 2% (2%)

7 -39 (1 ) 5% (0%) -39 (5) 5% (1 %)

8 -35 (10) 5% (1%) -38 (8) 5% (1%)

9 -85 (4) 12% (1%) -83 (4) 12% (1 %)

10 -36 (8) 5% (1%) -37 (8) 6% (1 %)

11 -50 (3) 6% (0%) -52 (7) 6% (1 %)
Grand Mean -39 (22) 5% (3%) -39 (22) 6% (3%)

 

 

 

 

 

 

 

The FR shear forces at the seat generally reached their minimum magnitudes and
inﬂected in the region when either leg was at its maximum height during a crank arm
revolution, i.e. 0° and 180°. Although this was readily apparent for the force proﬁle of
the subject shown previously in Figure 19, it was difﬁcult to conﬁrm a mean using
normal data reduction techniques when the timing angle values occurred at inconsistent
angles such as 0° = 360°. To better illustrate the timing angle for the minimum FR seat
force magnitude, a histogram of the ﬂequency of timing angle values was plotted in
Figure 20. With only a few exceptions, the minimum FR seat forces were clustered in the
regions near 0° and 180°, with 76% of the values in the range of 0-20° and 18% between

1 60- 190°.

59

Frequency

Figure 20: Histogram of Minimum FR Seat Force Timing Angles

 

300

250

200

150

100

50

 

0 1 80
Degrees

60

360

 

The range between the maximum and minimum FR seat force varied ﬂom 16N (6N) for
subject 9 to 57N (3N) for subject 7, with a grand mean of 39N (15N) while the left leg
was driving, and from 27N (8N) to 55N (7N) with a grand mean of 39N (13N) While the
right leg was driving.

Table 18: Range between the Maximum and Minimum FR Seat Forces

 

 

 

 

 

 

 

 

 

 

 

 

 

0-180° 180-360°
Subject Range (SD) Range (SD)
Newtons Newtons
0 32(7) 33(6)
1 48 (1 1) 47 (17)
3 23 (8) 35 (9)
4 45 (12) 36(8)
6 28 (8) 33 (8)
7 57 (3) 53 (8)
8 54 (6) 44 (9)
9 1 6 (6) 27 (8)
1 0 36 (1 3) 28 (7)
11 46(5) 55(7)
Grand Mean 39 (1 5) 39 (13)

 

 

 

 

 

61

Lateral Seat Forces

The lateral (side to side) seat force proﬁles displayed a single cycle of data per
crank arm revolution. Although this seems not to be similar with the vertical and FR seat
forces (which exhibited two force cycles per crank arm revolution), this force was the
only one that changed direction ﬂom right lateral during approximately 0-180° (a
positive force value), decreased to zero, then increased directed left laterally during 180-
360° (a negative force value). This change in direction showed as a sign difference in the

force magnitude measured by the load cell.

62

Two distinct proﬁles of the lateral seat forces became apparent within the group
of subjects tested. Although both proﬁles exhibit a single cycle of force data for every
complete revolution of the crank arms, one pattern was characterized by a “double
hump”, Figure 21 below. Three inﬂection points occurred during each phase (i.e. 0—180°
and 180-360°) of the crank arm revolution, and was seen in six of the ten subjects (0, l,

3, 6, 7, and 9).

Figure 21: “Double Hump” Lateral Seat Force Profile;
Single subject, single test

Degrees

 

40

ooo-s
ooo-s
coo-e

 

 

Force (N)
o

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

-40 7 ' 4 i

 

63

The remaining subjects (4, 8, 10, and 11) showed a “single hump” force proﬁle

per portion of the crank arm cycle, shown in Figure 22. As the left leg was driving the

Figure 22: "Single Hump" Lateral Seat Force Proﬁle;

 

Subject 4, Test 5
Degrees ’
60
:z':
8 0 i r i r *1 1 i T 4* ~ -
6 1 . :
“L i + l
. 1
l i '
l i ~
-60 ‘

 

 

 

crank arms the lateral seat force was directed away ﬂom the cycle to the right and
similarly, while the right leg was driving the lateral seat force was directed to the left of
the cycle.

With the left leg driving, the maximum lateral seat forces ranged ﬂom 20N (5N)
for subject 8 to 44N (7N) for subject 1 and were directed right laterally. The grand mean
was 31N (8N) and corresponded to a mean value of 4% BW (1%) across all subjects.
While the right leg was driving the lateral force magnitudes ranged ﬂom 22N (3N) to
46N (6N) and were directed left laterally, with a grand mean of 33N (8N). These forces

were equivalent to 5% BW (1%) across all subjects.

Table 19: Maximum Lateral Seat Forces;
Positive values were directed right lateral, negative values left lateral
(*-indicates subject displayed “Double Hump” Force Proﬁle)

 

 

 

 

 

 

 

 

 

 

 

 

0-180° Percent ISO-360° Percent
Subject Force (SD) Body Force (SD) Body
Newtons WQght Newtons Weight
0* 31 (4) 5% (1%) -29 (5) 5% (1%)
1 " 44 (7) 6% (1 %) -26 (5) 4% (1 %)
3* 29 (4) 4% (1%) -28 (4) 4% (1%)
4 34 (4) 4% (1 %) -46 (6) 6% (1 %)
6' 24 (8) 3% (1 %) -22 (3) 3% (0%)
7* 34 (9) 5% (1 °/o) -34 (9) 5% (1 °/o)
8 20 (5) 3% (1 %) -35 (7) 5% (1%)
9" 35 (4) 5% (1 °/o) -36 (3) 5% (0%)
10 26 (7) 4% (1 %) -36 (8) 5% (1%)
1 1 30 (3) 4% (0%) -37 (6) 5% (1 %)
Grand Mean 31 (8) 4% (1 %) -33 (8) 5% (1 %)

 

 

 

 

 

 

 

The timing angles of the maximum lateral seat forces ranged ﬂom 62° (4°) for
subject 7 to 155° (16°) for subject 9, with a grand mean of 92 (43) while the left leg was
driving. While the right leg was driving, the timing angles ranged ﬂom 240 (10) to 329
(30), with a grand mean of 266 (42). Standard deviations of approximately one third of
the evaluated regions occurred in several of the subjects, and were also reﬂected in the
standard deviations of the grand means. As examples, subject 3 showed a SD of 54°
while the left leg was driving (0-180°), while subject 1 showed an SD of 58° while the

right leg was driving.

65

Table 20: Lateral Seat Force Timing Angles
(*-indicates “Double Hump” Force Proﬁle)

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject 0-180° ISO-360°
Angle(SD)° Angle(SD)
0* 99 (49) 256 (31)
1" 113 (43) 290 (58)
3" 108 (54) 251 (36)
4 62 (4) 240(5)
6' 93 (53) 329 (30)
7* 63(4) 240 (10)
8 92 (37) 243 (32)
9* 155 (16) 309 (44)
10 72 (9) 252 (17)
11 63(4) 252(7)
Grand Mean 92 (43) 266 (42)

 

 

 

The range between the maximum lateral seat force magnitudes varied ﬂom 46N

(9N) in subject 6 to 79N (8N) in subject 4, with a grand mean of 63N (12N) across all of

the subjects.

Table 21: Range of Maximum Lateral Seat Forces

 

Subject

Force (SD)
Newtons

 

0

60 (5)

 

69 (8)

 

57 (6)

 

79 (8)

 

46 (9)

 

68 (15)

 

55 (9)

 

‘OQVOJ-hOD-e

71 (5)

 

10

62(11)

 

11

67 (7)

 

 

Grand Mean

 

63 (12)

 

 

66

 

 

Seat Pressure Mapping

Mapped pressure data ﬂom the seat were qualitatively analyzed to estimate
regions of contact that occurred between the seat and the subject’s pelvis and groin. The
pressure zones showing the greatest contact appeared to repetitively map out the shape of
the mid to anterior region subject’s pelvis over time. However, not immediately intuitive
were the patterns of moving contact regions between the seat and rider, especially at the
timing angles of the maximum seat forces.

In the regions of the crank arm revolution when the maximum vertical seat force
occurred, pressure data indicated greater contact on the opposite side of the seat ﬂom the
driving leg, and two similar patterns were noticed amongst the subjects tested. For
example, in the case where the left leg was driving the crank arms, mapped pressure

showed increased contact along the right side of the seat, as seen in Figure 23 below.

Figure 23: Top View of Seat Pressure Maps; Regions of
greatest contact (pressure > 3.1 N/cmz) at the maximum
vertical seat force while the left leg was driving

 

 

265mm 265mm

 

 

 

 

 

 

67

The maximum FR and lateral shearing seat forces occurred at approximately the
same timing angles during a crank arm revolution. These timing angle regions
(approximately 90° and 270°) presented the most anterior (furthest forward) regions of
contact between the rider and seat in the pressure data during a revolution of the crank
arms. The largest pressure magnitudes measured were greater than 3.10 N/cm2 (4.5 psi)
and appeared concentrated along the anterior pelvic ridge (bilaterally, the pubic ramii)
independent of the driving leg. When the maximum FR and lateral seat forces occurred,

Figure 24: Seat Pressure Map; Timing of the maximum FR and lateral seat

forces. Grey regions indicated the greatest contact areas between the seat and
rider (>3.1 N/cmz)

 

ﬁ-

265mm

 

 

 

.—

it appeared that the subject’s pelvis was rotated forward such that the rear regions of the
pelvis (the ischial tuberosities, or ITs) and buttocks supported no body weight.
Interestingly, this section of the seat was not contoured in the forward/rearward or

lateral directions, which indicated that the measured FR and lateral seat forces were likely

68

actual shear forces, rather than applied forces normal to the seat surface with some

forward/rearward contour orientation.

Handlebar Vertical Forces

In the Regular handlebar position, the maximum vertical handlebar forces ranged
ﬂom 55N (7N) to 107N (5N), and had a grand mean of 80N (15N) for the right handlebar
and 79N (15N) for the left handlebar. When normalized with respect to body weight it
was found that a maximum force equivalent to 11% (2%) of the body acted on each
handlebar that was always directed on the cycle towards the ground.

Table 22: Maximum Handlebar Vertical Force;
Negative values indicated a force directed downward

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VEiEiTal Percent Left Vertical Percent
Subject Body Weight Force (SD) Body Weight
Force (SD) (SD) Newtons (SD)
Newtons
0 ~80 (3) 13% (0%) ~64 (2) 10% (0%)
1 ~55 (7) 8 (1 °/o) ~75 (1 1) 1 1% (2%)
3 ~81 (4) 12% (1 °/o) ~99 (4) 14% (1 °/o)
4 -72 (3) 9% (0%) -73 (2) 9% (0%)
6 ~69 (11) 10% (2%) -55 (6) 8% (1 %)
7 ~91 (3) 13% (0%) ~79 (5) 1 1 % (1 °/o)
8 -107 (5) 14% (1 %) ~89 (4) 12% (1%)
9 ~81 (4) 12% (1%) ~82 (4.4) 12% (1%)
10 -7o (4) 10% (1%) ~67 (5) 10% (1%)
1 1 ~95 (3) 12% (0%) -1 02 (2) 13% (0%)
Grand Mean ~80 (15) 1 1% (2%) ~79 (15) 1 1% (2%)

 

69

 

The timing angle of the maximum handlebar forces varied across the subjects,
with a range of 7° (22°) to 74° (9°) for the right handlebar and 183° (26°) to 236° (5°) for
the left handlebar. The grand mean across the subjects was 44° (44°) for the right
handlebar and 217° (37°) for the left handlebar.

Table 23: Timing Angle of the Maximum Vertical Handlebar Force

 

 

 

 

 

 

 

 

 

 

 

 

 

Right Handlebar Left Handlebar
Subject Agle (SD) Angle (SD)
0 7 (22) 221 (24)
1 54 (43) 245 (60)
3 45 (24) 234 (20)
4 61 (70) 228 (34)
6 54 (38) 226 (17)
7 1 6 (38) 1 83 (26)
8 72 (28) 187 (10)
9 34 (45) 229 (31)
10 29 (52) 219 (32)
11 74 (9) 236(5)
Grand Mean 44 (44) 221 (34)

 

 

 

 

 

70

When the proﬁles of the right and left handlebar forces were viewed, it was
apparent that their standard deviations, presented in Table 23 above, may have resulted
ﬂom the somewhat ﬂat regions of force data that contained the maximum magnitude in
some of the cycles. These regions were represented ﬂom points A-B and C~D in the
handlebar vertical force proﬁle shown in Figure 25 below. It was clear that the maximum

magnitude at point A occurred in the beginning of the region, while for a subsequent

Figure 25: Handlebar Vertical Force Proﬁle; Single subject
in the Regular position

 

 

 

 

 

Degrees
-25 . . .
1 a1 .1
° 8 0 ‘8 l0 ,0 18
o o l l
1
5 1‘ (A '3:
§ 1
63 l
A; B
C.
-100 . . i

 

 

 

(_—_Rig_ht _— Left

cycle the maximum magnitude occurred at point D.

The minimum vertical force on the right handlebar ranged ﬂom -29N (8N) to -
72N (3N) with a grand mean of ~52N (13N). The minimum vertical force on the left
handlebar ranged ﬂom —35N (3N) to ~73N (3N) with a grand mean of ~48N (1 IN).

Again, the negative force values indicated a direction towards the ground on the cycle.

71

These forces ranged ﬂom the equivalent of 4% (1%) to 9% (0%) BW with a grand mean
of 7% (2%) BW on the right handlebar, and 5% (0%) to 9% (0%) BW with a grand mean
of 7% (1%) BW on the left handlebar.

Table 24: Minimum Handlebar Vertical Force

Negative Values Indicated a Force Directed Towards the Ground

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. Right Vertical Percent Left Vertical Percent
“me“ ﬂag?) Body Weight (so) F133;?) Body Weight (so)

0 -52 (3) 8% (1 %) -35 (3) 6% (1 %)

1 -29 (8) 4% (1 %) ~46 (9) 7% (1 %)

3 -45 (4) 6% (1 %) -49 (5) 7% (1%)

4 -50 (4) 6% (0%) -52 (2) 7% (0%)

6 45 (6) 7% (1 %) ~36 (3) 5% (0%)

7 -59 (7) 8% (1 %) -43 (7) 6% (1%)

8 '68 (5) 9°/o (1 °/o) -46 (5) 6°/o (1 %)

9 -57 (4) 8% (1 %) ~56 (3) 8% (0%)

1o 45 (4) 7% (1 %) -45 (2) 7% (0%)

11 -72 (3) 9°/o (0%) -73 (3) 9°/o (0%)
Grand Mean -52 (13) 7% (2%) ~48 (11) 7% (1%)

 

72

 

The timing angles for the minimum magnitude of vertical forces at the handlebars
ranged ﬂom 192° (20°) to 279° (7°) on the right handlebar and 17° (13°) to 54° (41°) for
the left handlebar. The grand mean timing angle was 229° (28°) on the right handlebar
and 33° (30°) on the left handlebar. The standarddeviations of 28° (right) and 30° (left)
in the grand mean timing angles represented approximately 8% of a full crank arm
revolution.

Table 25: Timing Angle of the Minimum Vertical Handlebar Load

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Handlebar Left Handlebar
Angle° (SD) Angle° (so)
0 192 (20) 31 (18)
1 232(25) 35(60)
3 227(20) 49(21)
4 239 (15) 33 (19)
6 235(28) 26(22)
7 216(15) 19(16)
8 232(21) 17(13)
9 223(8) 32(19)
‘0 217(20) 28(33)
‘1 279(7) 54(41)
Grand Mean 229 (23) 33 (30)

 

73

 

 

The range between the maximum and minimum vertical handlebar forces varied
ﬂom 22N (6N) to 39N (4N), or 4% (1%) to 5% (1%) BW, and had a grand mean of 28N
(7N) (4% (1%)BW) on the right handlebar. On the left handlebar, the range varied ﬂom
19N (5N) to SON (6N), or 3% (1%) to 7% (1%) BW, and had a grand mean of 30N (1 IN)
or 4% (1%) BW. Again, the maximum and minimum vertical handlebar forces were
always directed toward the ground on the cycle.

Table 26: Range between the Maximum and Minimum Vertical Handlebar Forces

 

 

 

 

 

 

 

 

 

 

 

 

 

. Right Vertical Percent Left Vertical Percent
S“°’°°t F123;?) Body Weight (so) ngaﬁ? Body Weight (so)

0 28 (3) 4% (0%) 28 (3) 4% (0%)

1 26 (6) 4% (1%) 30 (7) 4% (1 %)

3 36(4) 5% (1 %) 50 (6) 7% (1 %)

4 22 (6) 3°/o (1 °/o) 20 (3) 3‘70 (07o)

6 24 (7) 3% (1%) 19 (5) 3% (1%)

7 33 (7) 5% (1%) 37 (4) 5% (1 %)

8 39(4) 5% (1 %) 43 (4) 6% (1 %)

9 24 (4) 3% (1 %) 26(6) 4% (1 %)

10 25 (3) 4% (0%) 22 (4) 3% (1%)

11 23 (5) 3% (1 %) 29 (2) 4% (0%)
Grand Mean 28(7) 4% (1 %) 30 (11) 4% (1%)

 

 

 

 

 

 

Handlebar Forward/Rearward Forces

 

The maximum FR handlebar forces were about half that of the vertical force and
ranged ﬂom 24N (3N) to 54N (4N), with a grand mean of 40N (9N) on the right
handlebar and 40N (10N) on the left. The FR handlebar force values were equivalent to
6% (1%) of the subject’s body weight on either handlebar and were always directed

forward (away ﬂom the subject) on the cycle.

74

Table 27 : Maximum FR Handlebar Forces
Positive Values Indicated a Force Directed Towards the Front of the Cycle

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Right FR ”mm Left FR
Subject Force (SD) ‘3odyl Force (SD) Bod agree? SD
Newtons (:3) t Newtons y erg t( )
o 34 (1) 5% (0%) 28 (2) 4% (0%)
1 26 (3) 4% (0%) 43 (7) 6% (1%)
3 33 (3) 5% (0%) 46(2) 7% (0%)
4 46 (2) 6% (0%) 53(2) 7% (0%)
6 31 (5) 4% (1%) 24(3) 4% (0%)
7 43 (3) 6% (0%) 39 (3) 5% (0%)
8 50 (4) 7% (1 %) 39 (4) 5% (0%)
9 54 (4) 8% (1 %) 49 (3) 7% (0%)
1o 42 (5) 6% (1%) 29(4) 4% (1%)
11 42 (1) 5% (0%) 51 (2) 6% (0%)
Grand Mean 40(9) 6% (1%) 40 (10) 6% (1%)

 

75

 

The timing angles for the maximum FR handlebar forces varied across subjects
and ranged ﬂom ~16° (5°), or 344° (5°), to 103° (61°) for the right handlebar, and 170°
(26°) to 261° (48°) for the left handlebar. The grand mean timing angle for the maximum
FR handlebar forces was 48 (58) for the right handlebar and 212 (48) for the left

handlebar.

Table 28: Timing Angle of the Maximum FR Handlebar Force

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Handlebar Left Handlebar
Anal” (SD) Angleo (so)
0 -5 (18) 187 (24)
l 74 (47) 231 (48)
3 58 (38) 227 (44)
4 103 (61) 253 (29)
6 66 (34) 223 (27)
7 18 (56) 170 (26)
8 93 (45) 172 (22)
9 46 (5) 205 (65)
1° 63 (72) 261 (54)
‘1 23 (37) 190 (27)
Grand Mean 43 (58) 212 ( 48)

 

 

 

 

 

76

The timing angle data for the maximum vertical and FR right handlebar forces

were plotted together according to their ﬂequency of occurrence, Figure 26. No clear

Figure 26: Frequency of Right Maximum Vertical and FR
Handlebar Timing Angles

CI NormMax IAPMax

 

 

 

 

50

40 * * 1
6‘
ac, 30
3
E. 20
LL

10

o - .

0 90 180 270 360

Degrees

distinction of the mean timing angles could be made, other than they occur over a range
of approximately 100°. Although not shown, a similar pattern occurred for the left

handlebar forces, which would have ﬁlled in the remainder of the angles between 180°

and 360°.

77

The minimum FR handlebar forces ranged ﬂom 10N (4N) to 30N (3N) on the
right handlebar and 9N (2N) to 32N (3N) on the left handlebar, with a grand mean of 20N
(7N) and 19N (8N) respectively, as shown in Table 29. The FR handlebar force grand
means were equivalent to 3% (1%) BW on both the right and left handlebars and were

always oriented in the anterior (forward) direction on the cycle.

Table 29: Minimum FR Handlebar Forces;
Positive values indicated that the forces were directed forward on the cycle

 

 

 

 

 

 

 

 

 

 

 

 

 

Right FR Percent Left FR Percent
Subject Force (SD) Body Weight Force (SD) Body Weight
Newtons (SD) Newtons (SD)

0 18 (2) 3% (0%) 9 (2) 1% (0%)

1 10(4) 1% (1 %) 22 (4) 3% (1 %)

3 1 2 (3) 2% (0%) 18 (4) 3% (1 %)

4 26 (3) 3% (0%) 32 (3) 4% (0%)

6 17 (3) 2% (0%) 11 (2) 2% (0%)

7 18(5) 2% (1%) 10(4) 1% (1%)

8 28 (2) 4% (0%) 1 9 (5) 3% (1 °/o)

9 30 (3) 4% (0%) 28 (2) 4% (0%)

10 1 9 (4) 3% (1 °/o) 12 (2) 2% (0%)

11 22 (2) 3% (0%) 27 (3) 3% (0%)
Grand

20 (7) 3% (1 %) 1 9 (8) 3% (1 %)
Mean

 

 

 

 

 

78

 

 

The timing angle for the minimum right handlebar FR force ranged ﬂom 196° (27°) to
269° (6°) and had a grand mean of 240° (27°). For the left handlebar, the timing angle
ranged ﬂom 42° (34°) to 77° (57°), with a grand mean of 55° (28°). The standard
deviations of the grand means (27° for the right, 28° for the left) were similar to those
reported for the minimum handlebar vertical loads, and were approximately 8% of the
full crank arm revolution.

Table 30: Minimum Handlebar FR Force Timing Angles

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Handlebar Left Handlebar
MIKE (SD) Angle° (SD)
9 196(27) 65(10)
1 243(29) 77(57)
3 238(27) 59(16)
4 248(13) 50(13)
3 257(30) 47(11)
7 234(9) 46(10)
9 246(18) 42(34)
9 238(14) 47(27)
‘9 229(16) 45(22)
‘1 269(6) 71(26)
Grand Mean 240 (27) 55 (28)

 

79

 

The range between the maximum and minimum handlebar F R forces varied ﬂom
14N (4N) to 25N (5N) on the right handlebar and 14N (3N) to 29N (3N) on the left
handlebar, with grand means of 20N (5N) and 21N (5N), respectively. The ranges
between the maximum and minimum handlebar FR forces varied ﬂom 2—3% on the right
handlebar and 2-4% on the left handlebar, with grand means equivalent to 3% (1%) of
BW on both the right and left handlebars.

Table 31: Range between the Maximum and Minimum FR Handlebar Forces

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Right FR Percent Left FR Percent
Subject Force (SD) Body Weight Force (SD) Body Weight

Newtons (SD) Newtons (SD)

0 16 (2) 2% (0%) 19 (2) 3% (0%)

1 1 7 (3) 2% (0%) 21 (5) 3% (1 %)

3 21 (3) 3% (0%) 27(4) 4% (1%)

4 21 (4) 3% (1%) 21 (3) 3% (0%)

6 14 (4) 2% (1%) 14 (3) 2% (0%)

7 25 (5) 3% (1 %) 29(3) 4% (0%)

8 21 (2) 3% (0%) 19 (3) 3% (0%)

9 24 (4) 3% (1 %) 21 (3) 3% (0%)

10 23 (4) 3% (1%) 18 (3) 3% (1%)

11 20 (2) 3% (0%) 24 (2) 3% (0%)

Grand Mean 20 (5) 3% (1 %) 21 (5) 3% (1 °/o)

 

Handlebar Lateral Forces

 

The right and left maximum lateral handlebar forces were the smallest handlebar
forces measured. These forces were not calculated as a percentage of body weight
(%BW), as the result would have been less than 1% in most cases. Insufﬁcient data was
collected on the left handlebar lateral forces for Subject 0 and were not included in this

analysis. Similar to the lateral pedal and seat data, positive values indicate a force

80

directed towards right lateral, and negative values indicate forces directed towards left
lateral.

The maximum values of the lateral right handlebar force ranged ﬂom 5N (1N) to
20N (1N) and had a grand mean of 13N (1N), while the left handlebar ranged ﬂom —2N
(2N) to —16N (1N) and had a grand mean of —9N (5N). The maximum forces measured
on the right handlebar were directed right laterally as indicated by their positive value,
while the negative values on the left handlebar were directed left laterally.

Table 32: Maximum Lateral Handlebar Forces

Positive Force Values Indicated Forces Directed Right Lateral,
Negative Values Indicated Forces Directed Left Lateral

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Lateral Force Left Lateral Force
Newtons (SD) Newtons (SD)

0 6(1) -

1 5(1) -5 (3)
3 16(2) ~16 (1)
4 15(1) -10 (1)
3 10(3) -2 (2)
7 14(1) -3 (1)
8 16(2) -9 (1)
9 20(1) -15 (2)
‘9 14 (1) -8 (2)
1‘ 15(1) -14 (1)

Grand Mean 13 (5) _9(5)

 

81

 

The timing angles of the maximum handlebar lateral forces ranged ﬂom 7° (25°)
to 79° (23°) on the right handlebar and had a grand mean of 50° (41°), while on the left
handlebar the timing angles ranged ﬂom 181° (41°) to 257° (13°) with a grand mean
timing angle of 226° (51°).

Table 33: Maximum Handlebar Lateral Force Timing Angles

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Handlebar Left Handlebar
Angle° (SD) Argle° (SD)

0 7(25) -
l 75(47) 200(104)
3 65(25) 230(19)
4 46 (40) 251 (7)
3 75(35) 219(74)
7 19(17) 181(41)
9 79(23) 231(26)
9 65(34) 250(6)
‘9 26(49) 257(13)
‘1 44(33) 220(36)

Grand Mean 50 (41) 226 (51)

 

 

 

 

 

The minimum lateral handlebar forces, again directed right laterally with positive
values and left laterally with negative values, were the smallest forces measured in this
analysis. The minimum lateral right handlebar forces ranged ﬂom —3N (3N) to 9N (2N)
with a grand mean of 2N (4N). On the left handlebar, the minimum lateral forces ranged
ﬂom —5N (IN) to 4N (2N) with a grand mean 1N (4N).

Two of the subjects minimum force values on the right handlebar switched
direction (from right to left lateral) compared to the maximum value, one had a zero

minimum force value, and seven continued to load the handlebar towards right lateral.

82

Five of the subject’s minimum force values on the left handlebar were directed right
laterally, one went to zero, and two subjects force values remained directed left laterally.
Table 34: Minimum Lateral Handlebar Forces

Positive Force Values Indicated Forces Directed Right Lateral,
Negative Values Indicated Forces Directed Left Lateral

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Lateral Force Left Lateral Force
Newtons (SD) Newtons (SD)
0 -1 (1) --
l -3 (3) 4(2)
3 0(1) 0(1)
4 2(3) 0(1)
3 1 (3) 4(1)
7 2 (1) 4(1)
3 3(2) 2(1)
9 9(2) -5 (1)
‘3 4(1) 1 (2)
‘1 5 (1) -5 (1)
Grand Mean 2 (4) 1(4)

 

 

 

 

 

83

The timing angles of the minimum lateral handlebar forces ranged ﬂom 225°
(12°) to 274° (8°) and had a grand mean of 252° (26°) on the right handlebar. The timing
angle of the minimum lateral handlebar forces ranged ﬂom 29° (36°) to 79° (22°) on the
left handlebar, with a grand mean of 49° (38°). ,

Table 35: Minimum Lateral Handlebar Force Timing Angles

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Subject Right Handlebar Left Handlebar
Angle° (SD) Angle° (SD)
0 253(19) --
1 264(43) 65(69)
3 253(6) 60(17)
4 245(18) 32(25)
6 267(35) 79(22)
7 232 (19) 45 (33)
3 250(22) 49(33)
9 263(6) 44(24)
10 225(12) 34(39)
11 274(8) 29(36)
Grand Mean 252 (26) 49 (38)

 

 

 

 

 

84

The range between the maximum and minimum handlebar lateral forces varied
ﬂom 7N (IN) to 16N (2N), with a grand mean of 1 IN (3N) on the right handlebar. For
the left handlebar, the range again varied between 7N (1N) and 16N (1N), with a grand
mean of 10N (3N). Data was incomplete for theleft handlebar in all tests performed by
Subject 0.

Table 36: Range between the Magnitude of the Maximum and Minimum

Handlebar Lateral Forces

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Right Lateral Left Lateral
Subject Force Range Force Range
Newtons (SD) Newtons (SD)
0 7 (1) --
1 8 (3) 9 (4)
3 16 (2) 16 (1)
4 13 (3) 9 (2)
6 9 (2) 7 (2)
7 12 (2) 7(1)
8 13(1) 11 (1)
9 11 (2) 10 (2)
10 11 (1) 9(2)
11 10 (2) 9(1)
Grand Mean 11 (3) 10(3)

 

85

 

Signiﬁcant Effects due to Changes in Handlebar Position

The force and timing angle values presented in the previous section were for the
Regular handlebar position. In this section of Results, statistical comparisons of the
measures recorded in the Regular handlebar position were made to those obtained ﬂom
the Close and Far handlebar positions. In all, the grand means of 43 force and timing
angle measures each were compared for the seat and handlebars, as well as 17 measures
of the pedal forces. These included maximum and minimum forces, timing angles of the
maximum and minimum forces, and ranges between the maximum and minimum forces.
The null hypothesis was that zero differences existed in the grand means of the measures
across all subjects with a change in handlebar position.

At a conﬁdence interval of 95% (level of signiﬁcance a=0.05), there would be a
high probability that a change in handlebar position affected a measure for those values
where P<0.05. For this analysis however, any measure that had a value of P< 0.15
between at least two of the handlebar positions tested were included in the tables that
follow, on the basis that further study may be needed to clarify a relationship between

that measure and the change in handlebar position.

Pedal Measures

Of the 17 different measures observed ﬂom the pedal loads, three of the force
values were signiﬁcantly affected (P < 0.05) in at least one change of the handlebar
position, i.e. ﬂom Close-Far, Close-Regular, or Far-Regular, Table 37below. The
maximum tangent force to left crank arm path was nearly signiﬁcant ﬂom Close-Regular

and Far-Regular, with P = 0.078 and 0.0870 respectively, Table 38.

86

Table 37 : Mean Pedal Forces That Showed a Statistically Signiﬁcant Difference at
P < 0.15 for at Least One Handlebar Position Change, i.e. Close-Far, Close-Regular,
or Far- Regular

 

Close Regular Far
Position Position Position
Force (SE) Force (SE) Force (SE)

Newtons Newtons Newtons
Max Left Tangent to Crank Arm Path 180.0 (6.8) 172.8 (6.6) 179.3 (6.6)

Measure

 

 

 

 

Max Left Pedal Lateral 40.6 (2.9) ~38.2 (2.8) 40.8 (2.8)
Min Left Pedal Lateral 6.2 (1.1) 7.2 (1.1) 6.7 (1.1)
Min Right Pedal Lateral ~3.8 (0.8) -5.0 (0.8) 4.0 (0.8)

 

 

 

 

 

 

Table 38: Probability of Zero Difference in Pedal Forces

With a Change in Handlebar Position;
P< .05 indicated with Bold Font
P< .15 indicated with *

 

Close- Close— Far-
Measure Far Regular Regular
P = P = P =

 

Max Left Tangent to Crank Arm
0.8506 0.0778" 0.0870'

 

 

 

Path
Max Left Pedal Lateral 0.8520 0.0428 0.0163
Min Left Pedal Lateral 0.2784 0.0252 0.2056
Min Right Pedal Lateral 0.6457 0.0178 0.0373

 

 

 

 

 

 

Table 39: Pedal Force Timing Angles That Showed a Statistically Signiﬁcant
Difference of P < 0.15 for at Least One Handlebar Position Change, i.e. Close—Far,
Close-Regular, or Far-Regular

 

Close Regular Far
Measure Position Position Position
Angl_e ° (SE) Angl:e ° (SE) Alﬁe ° (SE)
Max Left Tangent to Crank Arm Path 103.2 (3.3) 104.4 (3.3) 102.1 (3.3)

Min Left Tangent to Crank Arm Path 277.6 (2.3) 281.4 (2.1) 277.0 (2.1)

 

 

 

 

 

 

 

 

87

Table 40: Probability of Zero Difference in Pedal Force Timing Angles
With a Change in Handlebar Position;
P< .05 indicated with Bold Font
P< .15 indicated with *

 

Close- Close— Far-

 

 

Measure Far Regular Regular
Max Left Tangent to Crank Arm
Path 0.4234 0.4053 0.0767'
Min Left Tangent to Crank Arm
Path 0.8294 0.1 209' 0.0573‘

 

 

 

 

 

 

Seat Measures

The seat forces affected by change in the handlebar position are shown in Table
41 below, and are also presented in terms of percent body weight (%BW) in Table 42.
All measures with force values signiﬁcantly affected by a change in handlebar position

were also affected in terms of %BW.

88

Table 41: Mean Seat Forces That Showed a Statistically Signiﬁcant Difference at
P < 0.15 for at Least One Handlebar Position Change, i.e. Close-Far, Close-Regular,

 

 

 

 

 

 

 

 

 

 

 

or F ar-Regular
Close Regular Far
Measure Position Position Position
Force (SE) _ Force (SE) Force (SE)
Newtons Newtons Newtons
Max Seat Vertical ~353.3 (17.6) ~368.7 (17.9) ~371.7 (17.5)
0~180
Max Seat Vertical ~358.5 (14.9) ~363.6 (14.8) ~368.3 (14.8)
180-360
Min Seat Vertical ~284.6 (15.9) -291.7 (15.7) -291.5 (15.8)
0~180
Min Seat Vertical ~284.7 (14.6) -291.5 (14.5) 295.5 (14.5)
180360
Max Seat FR ~77.9 (5.8) ~77.9 (5.7) ~83.1 (5.7)
0~180
Max Seat FR ~78.4 (6.1) ~78.6 (6.1 ) ~85.2 (6.1)
180-360
Min Seat FR 40.0 (6.2) -39.2 (6.1) 43.3 (6.1)
0~180
Min Seat FR 41.0 (6.2) -39.4 (6.1) 43.9 (6.1)
180-360
Range of Max and Min
37.4 (3.2) 39.2 (3.1) 41.3 (3.1)
FR Forces

 

 

 

 

 

Table 42: Mean Seat Forces in %BW that showed a Statistically Signiﬁcant
Difference of P< 0.15 for at Least One Handlebar Change, i.e. Close-Far, Close-

 

Regular, or Far-Regular
Close Regular Far
Measure Position Position Position
% BW (SE) ~%BW (SE) %BW (SE)

 

Max Seat Vertical

49.3% (1.8%)

51.4% (1.8%)

51.8% (1.8%)

 

 

 

 

 

 

 

 

 

 

0~180°

Maxs°atvem°3 50.0%(1.4%) 50.7%(1.3%) 51.3%(1.3%)
180-360°

M1" Sealvemca' 39.7%(1.8%) 40.7%(1.8%) 40.6%(1.8%)
0~180°

Mi" Seatvemca' 39.7%(1.6%) 40.7%(1.6%) 41.2%(1.6%)
180-360°

M93631” 10.8% (0.8%) 11.0% (0.8%) 11.6% (0.8%)
0~180°

Max 39311:“ 10.9% (0.8%) 11.0% (0.8%) 11.9% (0.8%)
180-360°

Mi" 99411:“ 5.6% (0.9%) 5.5% (0.9%) 6.1%(0.9%)
0~180°

Mi" 39311:“ 5.7% (0.9%) 5.5% (0.9%) 6.2% (0.9%)
180-360°

 

 

90

 

Table 43: Probability of Zero Difference in Seat Forces

With a Change in Handlebar Position;

P< .05 indicated with Bold Font

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P< .15 indicated with *
Close-Far Close- Far-Regular
Measure _ Regular _
P-- P= P-
Max Seat Vertical 0~180° 0.0013 0.0001 0.4814
%BW Max Seat Vertical 0~180° 0.0012 0.0001 0.4711
Max Seat Vertical 180-360° 0.0117 0.1844 0.1898
%BW Max Seat Vertical180-360° 0.0117 0.1755 0.1999
Min Seat Vertical 0~180° 0.1519 0.1429" 0.9716
%BW Min Seat Vertical 0~180° 0.1754 0.1499" 0.9261
Min Seat Vertical 180-360° 0.0031 0.0604" 0.2311
%BW Min Seat Vertical 180-360° 0.0036 0.0580" 0.2589
Max Seat FR 0~180° 0.0187 0.9753 0.01 17
%BW Max Seat FR 0~180° 0.0138 0.9521 0.0090
Max Seat FR 180-360° 0.0016 0.9434 0.0008
%BW Max Seat FR 180-360 0.0015 0.9414 0.0008
Min Seat FR 0~180° 0.1288' 0.7262 0.0425
%BW Min Seat FR 0~180° 0.1163" 0.7633 0.0421
Min Seat FR 180-360° 0.1754 0.4512 0.0223
%BW Min Seat FR 180-360° 0.1519 0.4755 0.0200
Range of Max and Min FR Forces) 0.0091 0.2295 0.1224"

 

 

 

 

 

Several timing angles for the seat forces showed signiﬁcant differences with a
change in handlebar position, Table 44. It was stated previously in the Results section
however, that the grand mean timing angles of the maximum seat vertical forces could
not be conﬁrmed. These results were presented here for completeness, but should be

considered carefully.

91

Table 44: Mean Seat Force Timing Angles That Showed a Statistically Signiﬁcant
Difference of P < 0.15 for at Least One Handlebar Position Change, i.e. Close-Far,
Close-Regular, or Far-Regular

 

 

 

 

 

 

 

Close Regular Far
Measure Position Position Position
Angle ° (SE) Angle ° (SE) Angle ° (SE)
Max Seat Vertical
113.6 (11.1) 108.5 (10.8) 92.8 (10.8)
Angle 0~180°
Max Seat Vertical Angle
265.6 (13.3) 288.5 (13.0) 283.1 (13.0)
180-360°
Max Seat FR Angle 180-
2692 (5.6) 267.5 (5.4) 275.4 (5.4)
360°
Max Seat Lateral Angle
102.3 (9.9) 92.0 (9.6) 102.9 (9.6)
0~180°
Max Seat Lateral Angle
269.4 (9.3) 266.2 (9.1) 260.6 (9.1)
180-360°

 

 

 

 

 

 

Table 45: Probability of Zero Difference in Seat Force Timing Angles
With a Change in Handlebar Position;
P< .05 indicated with Bold Font

 

 

 

 

 

 

P< .15 indicated with *
l -
Measure Close-FarlClose~Regular Far Regula
P = P = P =
Max Seat Vertical
0.0022 0.4533 0.01 1 8
Angle 0~180°

Max Seat Vertical Angle 180-360° 0.0233 0.0032 0.4477
Max Seat FR Angle 180-360° 0.1196" 0.6728 0.0321
Max Seat Lateral Angle 0~180° 0.9241 0.1 195" 0.0729
Max Seat Lateral Angle 180-360° 0.088 0.5282 0.2407

 

 

 

 

 

 

92

Handlebar Measures

Of the 43 measures compared at the right and left handlebars, 13 force values, six
%BW values, and eight timing angle values were signiﬁcantly affected by at least one
variation of the handlebar position. Similar to the seat forces mentioned previously,
signiﬁcance was seen in both the handlebar forces and their corresponding expressions
terms of %BW.
Table 46: Mean Handlebar Forces That Showed a Statistically Signiﬁcant

Difference at P<0.15 for at Least One Handlebar Position Change,
i.e. Close-Far, Close-Regular, or Far-Regular

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Close Regular Far
Measure Position Position Position
Force (SE) Force (SE) Force (SE)
Newtons Newtons Newtons
Max Right Vertical ~83.4 (4.1) ~80.0 (4.1) ~81.3 (4.1)
Max Left Vertical ~81.6 (4.6) ~78.5 (4.6) ~78.8 (4.6)
Min Left Vertical ~50.8 (3.1) ~48.3 (3.1) ~46.2 (3.1)
Max Right FR 36.9 (2.8) 40.2 (2.7) 44.1 (2.7)
Max Left FR 38.7 (3.3) 40.1 (3.3) 44.0 (3.3)
Min Right FR 18.1 (1.8) 20.0 (1.8) 20.6 (1.8)
Max Right Lateral 13.4 (1.7) 13.1 (1.6) 14.2 (1.6)
Min Right Lateral 1.4 (1.0) 2.1 (1.0) 2.4 (1.0)
Range of Max and Min
_ , 30.3 (2.4) 27.9 (2.3) 30.1 (2.3)
Right Vertical
Range of Max and Min
, 30.8 (3.5) 30.3 (3.5) 32.7 (3.5)
Left Vertical
Range of Max and Min
, 18.8 (1.5) 20.2 (1.4) 23.5 (1 .4)
Right FR
Range of Max and Min
20.2 (1.6) 21.3 (1.5) 25.9 (1.5)
Left FR
Range of Max and Min
, 12.0 (1.2) 11.0 (1.1) 11.9(1.1)
Right Lateral

 

 

 

 

 

 

93

Table 47 : Mean Handlebar Forces in %BW that Showed a Statistically Signiﬁcant
Difference of P< 0.15 for at Least One Handlebar Change, i.e. Close-Far, Close-

 

 

 

 

 

 

 

 

RegularJ or Far-Regular
Close Regular Far
Measure Position Position Position

% BW (SE) %BW (SE) %BW (SE)
Max Right Vertical 1 1 .6°/o (0.5°/o) 1 1 .2°/o (0.5°/o) 1 1 .4°/o (0.570)
Max Left Vertical 1 1.4% (0.5%) 11.0% (0.5%) 11.0% (0.5%)
Min L811 Vertical 7.1 °/o (0.3970) 6.7°/o (0.3°/o) 6.4°/o (0.3%))
Max Right FR 5.1% (0.4%) 5.6% (0.4%) 6.2% (0.4%)
Max Left FR 5.4% (0.4%) 5.6% (0.4%) 6.1% (0.4%)
Min Right FR 2.5% (0.2%) 2.8% (0.2%) 2.9% (0.2%)

 

 

 

 

94

 

Table 48: Probability of Zero Difference in Handlebar Forces
With a Change in Handlebar Position;
P< .05 indicated with Bold Font

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P< .15 indicated with *
Measure Clo;e;Far Close-PR:gular Far-Regular
Max Right Vertical 0.1939 0.0427 0.4252
%BW Max Right Vertical 0.2211 0.0434 0.3834
Max Left Vertical 0.0234 0.012 0.7862
% BW Max Left Vertical 0.027 0.0123 0.7468
Min Left Vertical 0.0002 0.0414 0.0662"
%BW Min Left Vertical 0.0003 0.0405 0.0734'
Max Right FR <.0001 0.0161 0.0022
%BW Max Right FR <.0001 0.0168 0.0021
Max Left FR <.0001 0.1576 <.0001
%BW Max Left FR <.0001 0.1613 <.0001
Min Right FR 0.0164 0.0701" 0.5179
%BW Min Right FR 0.0139 0.0705" 0.4738
Max Right Lateral 0.3053 0.7571 0.1478"
Min Right Lateral 0.0876" 0.1993 0.642
Range of Max and Min Right 0.8614 00516“ 00538"
Vertical
Range of Max and Min Left Vertical 0.0822" 0.6141 0.015
Range of Max and Min Right FR <.0001 0.1432' 0.0002
Range of Max and Min Left FR <.0001 0.1772 <.0001
Range of Max and Min Right Lateral 0.9077 0.1245" 0.1226"

 

 

 

 

 

The timing angles that corresponded to a maximum or minimum force that

showed a signiﬁcant difference due to a change in the handlebar position are shown in

Table 49. The timing angle of the maximum right lateral force showed the largest

standard error of 135° t014.6° across the three positions, and the P values associated

with these measures should be considered carefully.

95

 

Table 49: Mean Handlebar Force Timing Angles That Showed a Statistically
Signiﬁcant Difference of P < 0.15 for at Least One Handlebar Position Change, i.e.
Close-Far, Close-Regular, or Far-Rgular

 

 

 

 

 

 

 

 

 

 

Close Regular Far
Measure Position Position Position
Angle ° (SE) Angle ° (SE) Angle ° (SE)
Max Right Vertical
Angle 34.9 (7.3) 44.5 (6.8) 42.5 (6.8)
Max Left Vertical
Angle 212.8 (6.8) 220.9 (6.4) 223.8 (6.4)
Min Right Vertical
Angle 236.0 (5.3) 229.2 (5.1) 226.5 (5.1)
Max Left FR Angle 218.2 (9.8) 211.8 (9.3) 224.0 (9.3)
Min Right l=R Angle 243.0 (5.6) 239.9 (5.4) 236.0 (5.4)
Min Left FR Angle 58.4 (4.6) 54.9 (4.2) 49.0 (4.2)
Max Right Lateral
Angle 86.1 (14.6) 107.6 (13.5) 114.1 (13.5)
Min Right Lateral
Angle 243.6 (4.9) 252.5 (4.5) 235.6 (4.5)

 

 

 

 

 

Table 50: Probability of Zero Difference in Handlebar Force Timing Angles
With a Change in Handlebar Position;
P< .05 indicated with Bold Font

 

 

 

 

 

 

 

 

 

P< .15 indicated with *
Measure C 10;:F ar C lose-PR:gular F ar~1;e=gular
Max Right Vertical Angle 0.2394 0.1400" 0.7446
Max Left Vertical Angle 0.0461 0.1413" 0.5667
Min Right Vertical Angle 0.0277 0.1157" 0.4903
Max Left FR Angle 0.4548 0.4062 0.0877"
Min Right FR Angle 0.069" 0.4212 0.2687
Min Left FR Angle 0.061 " 0.4804 0.2066
Max Right Lateral Angle 0.0599" 0.1467" 0.6396
Min Right Lateral Angle 0.0793" 0.0529“ <.0001

 

 

 

 

 

96

 

Discussion and Conclusions

Baseline Rider/Cycle Interface Seat and Handlebar Forces

On the premise that skin, groin, and other non-traumatic cycling injuries may be
the result of combined loading at the rider/cycle interfaces, the ﬁrst goal of this research
was to describe the baseline vertical and shear force values at the rider/cycle interfaces.
Also evaluated were the corresponding timing angles (the left crank arm angles at which E]
the maximum and minimum forces occurred). Both the forces and timing angles were E
measured for a bicycle ﬁtting approach commonly used in commercial settings to

properly adjust the bicycle handlebars at the correct reach ﬂom the seat.

Seat Forces

During a single crank arm revolution, the data support the conclusion that
consistent loading was applied to the groin region during all of the cycling tests. For
example, the vertical and forward/rearward (AP) shear forces were never zero, and both
exhibited a cyclical proﬁle that cycled between the maximum and minimum forces
(always negative magnitudes) twice per crank arm revolution. This indicated that the
vertical forces always acted in the downward direction and the FR forces acted in the
rearward direction on the cycle. This ﬁnding supported two other pieces of work, and
also described the double cycle of these forces. Bolourchi and Hull (1985) described the
proﬁle of the measured force along the axis of the bicycle seat tube as reactive to the
pedal loads for three subjects, which displayed a “double cycle” proﬁle for every crank

arm revolution, one attributed to each legs contribution to driving the crank arms of the

97

cycle. Stone and Hull (1995) also noted a similar pattern with the measured FR seat
force in tests of ﬁve subjects.

In contrast to the vertical and FR seat forces the lateral, or side to side, seat shear
forces were relieved once per crank arm revolution and displayed a “single cycle” force
proﬁle, as the force magnitude went to zero and then switched direction from left lateral
to right lateral. As the left leg drove the crank arms the positive force magnitude on the
seat indicated the lateral shear force was directed to the right on the cycle, or to the left
on the subject. Similarly, when the right leg was driving the negative force magnitudes
indicated the forces were directed to the left on the cycle or to the right on the subject.
This suggested that the lateral seat forces were related to the pedal reaction forces.

The grand mean of the vertical seat forces alternated between a minimum of 41%
of the subjects’ body weight (% BW) (292N, standard deviation (SD) 49N) and a
maximum 52% BW (372N (56N)) in the Regular position. As expected, the vertical seat
forces were the largest measured forces at any of the rider/cycle interfaces. Presented in
the Introduction, other authors have theorized these forces were directly related to groin
injuries such as occluding blood and oxygen ﬂow to the surface of the skin and other
internal body parts, nerve entrapment, bruising, skin ulceration, and erectile dysfunction.

The maximum vertical forces expressed in %BW found during cycling were
lower than those found under the buttocks of subjects in other seated postures (i.e. ofﬁce
chairs or automobile seats). Bush (2000) showed that approximately 53-56% of a
subject’s body weight was supported by the buttocks, and was dependant on the subject’s
position in the chair. This is an interesting ﬁnding, as non-traumatic injuries attributed to

cycling (bruising, perineal and genital numbness, impotence, “accessory testicles”) are

98

generally not experienced by individuals in other seated postures. This likely resulted
ﬂom many differences between the two postures, which included contact area between
the seat and subject, temperature, and moisture. Another factor that should be considered
was the cyclical nature of the shear forces in cycling. Also, unique to the cycling posture
the body weight was partially supported in the anterior areas of the groin (the perineum)
in addition to the buttocks, as contact was consistently shown through mapped pressure
data in this region.

Shear forces have been mentioned in literature as secondary causative factors in
non-traumatic skin injury, but until now were overlooked in terms of quantitative data.
The seat shear forces acting in the forward/rearward (FR) direction alternated between
5% and 11% BW (39N (22N) to 78N (20N)), and were always directed forwards on the
groin of the rider. Similar to the vertical seat forces, the FR shear forces were
consistently negative throughout the crank arm revolution, never reached zero, and were
directed rearward on the cycle. As such, the FR shear continuously pushes the tissue of
the groin forward, and Bennett et al. (1979) described the respective compressive and
tensile states of the tissue immediately forward and rearward of the contact zone. In their
work, Bennett et al. also pointed to the fact that both of these tissue states acted to resist
motion at the contacting surfaces, so their measurement device likely registered less force
than was actually present in the tissues immediately forward and rearward of the contact
zone. Though they explained acceptably small amounts of error for their test condition,
they also postulated that larger force value errors (i.e. larger forces in the tissue than
actually measured) would be present in data obtained testing skin over bony prominences

than over muscle mass. Making a similar comparison in the cycling activity (i.e. with the

99

skin of the groin pressed into the bony prominences of the pelvis) the shear force
magnitudes in the skin of the groin adjacent to its contact zones with the seat may have
been larger than were measured.

In contrast to the FR seat forces, the lateral seat forces reached their maximum
magnitudes and then were momentarily relieved in the transition between the periods of
the left and right leg driving the crank arms of the cycle. The lateral force magnitudes
reached maximums of 4% to 5% BW (3 IN (8N) to 33N (8N)), and were always directed
away ﬂom the driving leg on the cycle.

As discussed in the Results, two different lateral seat force proﬁles were observed
among the subjects tested. Six subjects displayed a “double hump” proﬁle, while four
displayed a “single hump” proﬁle. Generally, the subjects who displayed the “double
hump” proﬁle had standard deviations in their timing angles much greater than those that
displayed the “single hump” proﬁle. However, this was expected after it was noticed that
the larger force magnitude could have occurred at either the ﬁrst or second “hump”.
While this difference was noted, no inferences were made as to causal factors between
the subjects that displayed one proﬁle or the other. One possibility for the difference seen
in the force proﬁles may have been related to a subject’s efﬁciency in producing power
around the crank arm revolution. Another explanation may have been that the different
proﬁles were somehow related to muscle activation and coordination differences between
subjects.

It was recognized that the measured magnitudes of the seat shear forces were a
ﬂaction (approximately 10% to 20%) of the vertical force magnitudes, but their

secondary contribution in occluding blood ﬂow to the surface of the skin in the palm has

100

been examined. Bennett et al (1979) found that when exposed to shear stress values of
approximately 0.981 N/cm2 (100 g/cmz), only half the magnitude of normal pressure
(compared to the no shear stress condition) was necessary to occlude blood ﬂow. Based
on this, a reduction in the magnitudes of the shear forces at the rider/seat interface could
delay the onset and decrease the severity or occurrence of non-traumatic skin injuries at
the groin. These forces may be under one’s control to manage through the design and
shape of the seat, or through changes to the seat and handlebar position. Perhaps future
work could assess the shear force values between different seat designs, for example

those with cutouts and those without.

Handlebar Forces

Maximum and minimum handlebar forces were collected from the right and left
hand once per crank arm revolution as the vertical, FR shear, and lateral shear forces at
the handlebars exhibited a single cycle force proﬁle per crank arm revolution. This
ﬁnding was in contrast to the force proﬁles reported by Bolourchi and Hull (1985) and
Stone and Hull (1995), but their handlebar force data included the contributions ﬂom
both hands through a single dynamometer. To this author’s knowledge, the interface
forces measured individually at the right and left hands has not been previously reported.

Each of the hands supported vertical forces that ranged between a minimum of
7% BW (approximately 50N (12N)) and a maximum 11% BW (80N (15N)) averaged
across all of the subjects, and 8 FR shear force that ranged ﬂom 3% to 6% BW (20N (8N)
to 40N (10N)). The vertical forces were always directed on the handlebars towards the
ground, and the FR forces were always directed towards the ﬂont of the cycle. Thus the

vertical forces acted upwards and FR forces acted rearwards on the hands of the subject.

101

An aspect of the handlebar loading that has not been previously reported was the
asymmetrical loading shown between the right and left handlebar forces in several
subjects. Subjects 0, 6, 7, and 8 placed considerably (>15%) more load on the right hand
than the left, and subjects 1, 3, and 11 consistently placed more load on their left hand.
This asymmetrical loading may be due to various musculoskeletal imbalances, such as in
the back, pelvis, shoulders, and arms. Also, the difference in loading may be necessary
for balance as the loads transfer between all of the interfaces. A more involved
investigation of the kinematics of the rider’s body may provide further insight into this
observation.

The lateral handlebar forces had the smallest magnitudes, and were typically less
than 1% BW. The mean lateral forces magnitudes ranged ﬂom a minimum of IN to a
maximum of 13N across the ten subjects tested, and were reported here merely for

completeness of the data set.

Timing Angles

The grand mean timing angles for the minimum vertical seat force occurred in the
regions near 0° and 180° for the ten subjects tested. This conﬁrmed the timing angle data
presented by Bolourchi and Hull (1985) for their three subjects.

The grand mean timing angles for the maximum vertical seat forces were 108°
and 288° during their respective portions of the crank arm revolution (i.e. 0~180° or 180~
360°). While the mean timing angles were consistent for the most part within a set of
tests for a subject, they ranged approximately 100° amongst the ten subjects while either
the right or left leg was driving the crank arm. This resulted in standard deviations (SD)
for the grand mean timing angles of 38° and 45°, respectively.

102

A ﬁnding that was not immediately intuitive was the region of contact between
the rider and seat at the timing angle of the maximum vertical seat forces. Mapped
pressure data showed that the pelvis and buttock region opposite to that of the driving leg
was fully or primarily in contact with the seat rather than the same side. This ﬁnding
supported conclusions by Bolourchi and Hull (1985). Bolourchi and Hull theorized this
phenomenon ﬂom their evaluation of the moment proﬁles reactive to vertical loads on
the seat, and they attributed it to increased body weight being supported by the pedal of
the driving leg at the bottom of its pedal stroke.

At ﬁrst glance, comparison of the timing angles indicated the vertical seat forces
while may have occurred as a reaction to the forces tangent to the left crank arm path, as
they both occurred near the same timing angles. After looking at the standard deviations
of the timing angles in both cases however, those of the maximum and minimum forces
tangent to the crank arm path were more regular than those of the maximum and
minimum vertical seat forces. Therefore, it was theorized that the vertical seat forces
were more complicated than being simply reactions to the pedaling forces at the feet, and
that force contributions ﬂom the hands, as well as the kinematics of the rider’s body, may
also play a role.

The similarity of the mean timing angles of the vertical (44° (44°)) and FR
handlebar forces (48° (58°)) indicated that they generally occurred together. However,
with standard deviations equal to approximately one third of their respective regions of
occurrence (i.e. 0~180° or l80-360°), ﬁrrther work is needed to verify this ﬁnding. If in
fact they do occur together, it is possible that the magnitudes of these combined forces

would be sufﬁcient to cause injuries to the tissue of the hand or wrist (nerve compression,

103

tingling of the hands, swelling of the compartments of the wrist), especially if they were
highly localized to one region of the hand. This could be problematic if the hands were
left in one position for an extended amount of time, for example in the drop rather than
the top section of the handlebars or the brake hoods. In future work, pressure mapping at
the handlebars would be useful to estimate regions of localized contact that occurs

between the hand and handlebar.

Signiﬁcant Effects from Changes to Handlebar Position

The second goal of this work was to determine if changing the rider’s position
(through a change in the distance ﬂom the seat to the handlebars) signiﬁcantly affected
the interface forces and/or their timing angles.

The minimum and maximum vertical seat forces in this investigation were
signiﬁcantly affected by changes in the length ﬂom the seat to the handlebars. More of
the body weight was boum by the seat as the handlebars were moved further away ﬂom
the seat. This ﬁnding did not seem intuitive, as it was expected that more of the subject’s
weight would be supported at the seat as the body was brought into a more upright riding
position through adjustment of the handlebars closer to the seat.

Movement of the handlebars ﬂom the closest to the furthest handlebar position
resulted in the minimum vertical seat forces increasing ﬂom approximately 40% BW to
41% BW and the maximum vertical seat forces increasing ﬂom 49% BW to 52% BW.
While the minimum vertical seat forces increased approximately 1% BW with a position
change, the maximum forces increased approximately 3%. This resulted in an increased
range between the minimum and maximum forces as the handlebars were moved away

ﬂom the subject. The increased range between the forces must also be considered as a

104

factor in non-traumatic injuries, especially with increased time on the bicycle. For
example, at the tested pedaling ﬂequency of 75 RPM the forces cover this range of force
magnitudes approximately 9,000 times in a 30-minute ride, since the seat forces cycle
twice per complete crank arm revolution.

The FR seat forces were also signiﬁcantly affected by the change in handlebar
position. The maximum FR seat forces increased ﬂom 10.8% BW to 11.9% BW as the
handlebars were moved ﬂom the closest to the furthest handlebar position. The
minimum FR seat forces also increased ﬂom 5.5% to 6.2% BW, but the ranges between
the maximum and minimum force magnitudes were similar across all handlebar
positions.

The vertical and FR handlebar forces were also signiﬁcantly affected by the
change in handlebar position, though not as much nor as clearly as the vertical and FR
seat forces. Both the right and left handlebar vertical forces signiﬁcantly decreased ﬂom
12% BW to 11% BW with the change ﬂom the Close to the Regular position, but no
further decrease was noted as the handlebars were moved to the Far position. The FR
forces at each handlebar also increased signiﬁcantly approximately 0.5% BW with every
change in handlebar position (i.e., ﬂom 5% BW in the Close position to 6% BW in the
Far position).

The postures a bicyclist assumes have shown to affect the shape of the lumbar
spine, inverting its natural physiological (concave and lordotic) shape, and possibly
changing the loading characteristics of the discs (Usabiaga et al. 1997). Although there is
some adjustability to the height of the handlebars relative to the seat, changing the reach

is a costly proposal. Consumers must purchase a different length stem to properly adjust

105

reach to the handlebars. With only a limited range of stems lengths available,
adjustability of 5cm in either direction of a factory installed stem are about the maximum
adjustment available before changing to a different ﬂame size.

The seat of a standard bike allows for adjustment both vertically and fore/aft
without the need to purchase additional parts. Biomechanical studies have indicated
preferred seat height data for efﬁcient pedaling mechanics, optimized power output, and
the prevention of joint injury. For bicyclists with the seat height adjusted for appropriate
pedaling mechanics, any changes in the interface force distributions between the seat,
handlebars, and pedals may necessitate changes to the reach or relative height of the
handlebars to the seat.

The data presented here are the ﬁrst of their kind, and support the conclusion that
moving the handlebars closer to the seat signiﬁcantly decreases vertical and FR shear
loading on the seat. Also, the vertical forces at the handlebars signiﬁcantly increased,
while the FR forces decreased, as the handlebars were moved closer to the seat. It is
expected that this information will be useful in the development of future bicycle seats
and handlebars, as well as assist bicycle ﬁt experts in positioning riders on their bicycles

to reduce the occurrence and severity of non-traumatic injuries related to bicycling.

Pedal Data Comparisons

Finally, pedal forces and timing angles were collected for comparisons with
research performed by other authors. For the work presented here, timing angles were
referenced to the angle of the left crank arm as viewed ﬂom the left side of the cycle,
where a value of 0° indicated the left pedal was at its highest position in the y-z plane

during a crank arm revolution, and 180° indicated its lowest position. Mean (average)

106

maximum and minimum force values, along with their corresponding timing angles, were
calculated from ten complete cycles of force data as described by ten complete
revolutions of the crank arm.

Both the maximum and minimum left pedal force component tangent to the crank
arm path occurred at timing angles that were in a range consistent with previous research
(Neptune et al. 1999, Smak et al. 1999). Previously described in terms of crank torque
(N -m) rather than force tangent to the crank arm path (N), the difference was a scalar

multiplier of the crank arm length, as shown in Figure 27.

107

Figure 27: Representative Crank Torque Proﬁle for One Crank Revolution in a
Single Subject; Smak et al. (1999), Figure 1(a)

 

 

   

   

 

 

 

80 Crank Torque

w l-
A ‘4‘ 7“. Wilson
{5 ‘0 b 3;, Grand mean ‘
5 it , (28.5N-m) ;(~13.9N~m)
Q) .
a 20
’5
l— . ,

o 7 ..........
-zo. .
0 90 130 270 360

(a) Crank Angle (deg.)

Measured forces at the pedals were a combination of inertial effects ﬂom the
weight and movement of the legs, as well as muscular contributions ﬂom the legs,
buttocks, and lower back. When averaged across all subjects, the applied maximum force
of 173N (or 28.5N-m of torque with 165mm crank arms) tangent to the path ascribed by
the left crank arm occurred at a timing angle of approximately 104°, while a minimum
applied force of —84N (~13.9N-m torque) occurred at approximately 281°. The maximum
torque magnitudes were approximately half of those reported by Smak et al. (1999), but
this was expected ﬂom differences in the external power output required of the test
subjects (250 watts (Smak et al. 1999) vs. 125 watts for this work).

As these forces were perpendicular to the left crank arm, work was done to drive
the crank arms when the force values were positive, and work was done against the crank
arm during 180~360°. The local coordinate system of the right pedal was not attained in

this work but if symmetry were assumed, the right side forces tangent to the crank arm

108

path reached their maximum values with the left crank arm near 284° and their minimum
values with the left crank arm in the region of 101°.

Favorable comparisons to previous work done on the pedaling forces tangent to
the crank arm path, as well as their timing angles, suggested that the measurement
equipment used in this investigation were adequate for the study of cycling
biomechanics. Also, the techniques used during data reduction were also veriﬁed. This
was important to justify the order of the pedal force coordinate transformations, since

they were transformed into different coordinate systems twice.

109

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