INTERNATIONAL JOURNAL OF SPORT BIOMECHANICS, 1992, 8, 152.164
Design and Evaluation
of a Multi-Degree-of-Freedom
Foot/Pedal lntirface for Cycling
Dennis Wootten and Maury L. Hull
Described is the design of a foot/pedal interface intended as a research tool
in the study of overuse knee injuries in cycling. The interface enables the
systematic variation of factors that may affect loads transmitted by the knee
joint. It permits two degrees of freedom of movement, inversion/eversion
and abduction/adduction rotations, either separately or in combination. The
movement permitted by each degree of freedom can be either free or resisted
by spring assemblies. Sample data were collected to demonstrate the function
of the footlpedal interface. With no spring resistance, the interface functioned
as intended by allowing free movement of the foot. Significant interaction
was seen between the two degrees of freedom, with more motion and a larger
absolute mean occurring when both degrees of freedom were allowed
simultaneously. This emphasizes the need for a multi-degree-of-freedom
interface when undertaking a comprehensive study of the factors affecting
loads transmitted by the knee.
Knee pain is perhaps cycling's most common overuse injury, accounting
for approximately 25% of all reported cycling injuries (Gaston, 1977; Hannaford,
Moran, & Hlavac, 1986). These ailments typically result from a combination of
overuse and biomechanics (Pruitt, 1988). Pathomechanical cycling injuries are
overuse injuries that result from incompatibilities between the bicycle and the
bicyclist. Differences between the fixed motion patterns of the bicycle pedal and
the natural motion of the cyclist's foot are thought to contribute to pathomechanical cycling injuries (Francis, 1988).
During the power phase of cycling, when the foot is moving down it may
attempt to pronate (Francis, 1986), which is a combination of dorsiflexion,
abduction, and eversion (see Figure 1). If the foot cannot undergo this movement,
then compensatory motions are developed in other components. Such motion
may possibly be absorbed by the shoe and the slight play that exists with most
conventional shoelpedal systems (Zahradnik, 1990). However, pronation may be
restricted by stiff shoes and rigid shoelpedal connections, in which case the joints
must absorb the motions and the resulting loads. There has been an increase in
The authors are with the Department of Mechanical Engineering at the University
of California-Davis, Davis, CA 956 16.
Design of a Foot/Pedaf Interface
Forefoot
Abduction
Forefoot
Inversion
X
Forefoot
Adduction
Dorsifkxion
Y
Eversion
Plantarf lexion
Figure 1 - Orientation of axes and motions with respect to the right foot. The
origin is located at the ball of the foot with positive X anterior, positive Y medial,
and positive Z upward. Forefoot inversion/eversion are rotations about the X-axis,
plantarflexion/dorsifIexion are rotations about the Y-axis, and forefoot adduction/
abduction are rotations about the Z-axis.
injuries related to foot restraint as shoe uppers have become stiffer and strapless
pedals have locked the foot more firmly in place (Zahradnik, 1990).
In order to allow the foot complete angular mobility, three orthogonal axes
of rotation are necessary. The orientation of these axes relative to the foot is
described in Figure 1. Although they do not directly correspond with the
anatomical axes of the joints of either the foot or the ankle, motions about these
axes will allow unconstrained rotation of the foot while it is attached to the pedal.
An axis parallel to the y-axis, which allows the foot to dorsiflex and plantarflex,
is provided by the pedal spindle. Motions about the other two axes must be
provided by the pedal interface.
The ultimate goal of the research to which the present article pertains is
to investigate whether a pedal that allows for joint motions accompanying
pronation and supination will reduce the risk of pathomechanical knee injuries
during cycling. Knee forces and moments, calculated from pedal forces and
moments using a five-bar linkage kinematic model of the bicycle and bicyclist
(e.g., Ruby, Hull, & Hawkins, 1991), will be evaluated as potential sources of
overuse injury. It is assumed that reducing these forces and moments will benefit
the cyclists by reducing both the risk of injury and fatigue. Pedal forces and
moments will be measured by a six-load component pedal dynamometer with a
pedal interface that either can allow for pronation and supination or can be locked
Wootten and Hull
Y
Ctasp Hinge
Spring Assemblies
Linear Motion
Potentiometer
Concave Cylinder
B. Inversion/Eversion Mod
Axial ~ o t a t i o nModule
n Connecting Plate is not visible
Figure 2 - Pedal interface modules. The cleat connector provides the shoelpedal
connection. The cleat connector bolts to the convex cylinder of the inversion/eversion
module. The inversion/eversion module bolts to the axial rotation module through
the interface plate. The limits of rotation are +lo0 for both modules.
in a set position. The design of a pedal interface that allows the foot to pronate
and supinate is the focus of this paper.
Design Description
The pedal interface consists of three modules: the cleat connector, the inversion1
eversion module, and the axial rotation module (see Figure 2). The cleat connector,
Design of a Foot/Pedal Interface
155
shown in Figure 2a, provides the shoe/pedal connection. The interface uses a
Shimano cleat that fits snugly into the front of the cleat connector. A hinged
clasp rotates into the groove in the back of the cleat, and a pin locks the clasp
securely in place, rigidly restraining the shoe.
The inversion/eversion module, shown in Figure Zb, allows -t 10" of
rotation, which occurs through a pair of mating aluminum partial cylinders sliding
on each other. These surfaces are coated with Teflon-S to reduce friction and
wear. The cleat connector bolts to the rorating convex cylinder which transfers
downward forces to a mating, nonrotating concave cylinder below it. Thrust and
upward forces are transferred to tabs bolted to the front and rear of the concave
cylinder that fit into concave recessions in the convex cylinder. The clearances
between these tabs and the convex cylinder are adjustable to achieve smooth
rotation. A linear motion potentiometer is bolted through spherical bearings to
the convex cylinder at one end and to an arm extending laterally from the front
tab at the other end. Thus the potentiometer changes in length when the convex
cylinder rotates. Restoring moments can be provided by spring assemblies
mounted at the back of the module.
The axial rotation module, shown in Figure 2c, allows 10" of forefoot
abduction and adduction. The inversion/eversion module bolts to the interface
plate, which in turn bolts to the axial rotation plate. Free to rotate, the axial
rotation plate bears on the nonrotating cylinder housing below. Thus downward
axial loads are supported by the bearing surface. Support of radial loads is
achieved by bolting the axial rotation plate to a cylinder that fits into a mating
hole in the cylinder housing. Arms extending from the bottom of this cylinder
to the front and rear support upward axial loads, with the front arm actuating a
spring assembly and the rear arm connecting to a linear motion potentiometer
through a spherical bearing. The other end of the potentiometer is also bolted
through a spherical bearing to an arm extending laterally and integral with the
cylinder housing. Accordingly, the length of the potentiometer changes when the
rear arm rotates. These parts are also coated with Teflon-S to facilitate the relative
motion.
Interconnecting the three modules not only enables the degrees of freedom
offered by the individual modules but also enables adjustment of the position of
the axes of rotation relative to the foot while maintaining the foot in a reference
position relative to the pedal spindle. As indicated in Figure 3, the cleat connector
is bolted to the inversion/eversion module through two slots that allow for
1.25 cm of medialflateral translation of the foot relative to the modules below.
To obtain independent adjustments of the medialflateral position of both
axes of rotation relative to the foot, the inversion/eversion module bolts to the
interface plate of the axial rotation module below through slots in flanges on
either end of the inversion/eversion module. Thus, adjusting the cleat connector
mediallyflaterally moves the foot relative to the rotation axes of both modules,
while subsequent medialflateral adjustment of the inversion/eversion module
moves the foot relative to the axial rotation axis only. To obtain forelaft adjustment
of the foot relative to the axial rotation axis, the interface plate bolts to the axial
rotation plate through slots running forelaft.
Repositioning the foot to a reference position relative to the pedal spindle
following any or all of the above adjustments requires the capability for both
forelaft and medialPatera1 recentering. This capability is realized through a
Wootten and Hull
Adjustment o f t h e
Axial Rotation Axis
Cleat
Connector
Fore/Af t
Adjustment
Inversion/Eversion
Module
F o r e / A f t Recentering
MediaVLateral Recentering
(Slot Not Visible)
Figure 3 - Assembled modules. When assembled, the modules are interconnected
to enable adjustment of the axes of rotation relative to the foot while maintaining
the foot in a reference position relative to the pedal spindle.
1. Lock Nut
2. Spring Assembly Bracket
3. Piston Nut
4. Cylinder
5. Piston
6. Spring Actuator
7. Spring
Figure 4 - Spring assembly cross-section. The spring assemblies provide restoring
loads for both inversion/eversion and axial rotations. Each consists of a piston, piston
nut, spring, cylinder, and lock nut. The piston slides in the cylinder with external
loads resisted by a spring between the piston and cylinder.
connecting plate between the axial rotation module and the dynamometer below.
Forelaft recentering is achieved by bolting the axial rotation module through
slots in flanges on either side of the plate, and medialPatera1 recentering is
achieved through slots in flanges at either end of this plate where it bolts to the
dynamometer. Thus the slots in the side flanges permit the axial rotation module
to translate forelaft while the slots in the end flanges allow the connecting plate
(with axial rotation module attached) to translate medially/laterally.
The spring assemblies provide restoring moments for both inversion1
eversion and axial rotations. Diagrammed in Figure 4, each spring assembly
consists of a lock nut, piston nut, cylinder, piston, and spring. The spring assembly
Design of a FootIPedal Interface
A.
-
20
-
10
-
Linear Spring
B.
Linear Spring with Clearance
-
0
5
C
E
157
0-
a
3
-10
-
-20
-4
-8
0
4
8
Displacement (mm)
Displacement (mm)
C.
Preloaded Spring
Displacement (mm)
D.
Preloaded Spring with Clearance
Displacement (mm)
Figure 5 - Spring load vs. displacement curves. Spring assemblies can be set to
provide any of the four curves shown.
can be configured to provide the spring curves depicted in Figure 5. Setting both
the piston nut and the cylinder such that the spring is at its free length and the
pistons just contact the actuator gives the standard spring curve shown in Figure
5a. Threading the cylinder out of the spring assembly bracket with the piston nut
set so that the spring is at its free length creates a gap between the piston and
the spring actuator, giving the load-versus-displacement curve shown in Figure
5b.
Tightening the piston nut allows the spring to be preloaded. Preloading the
spring and setting the cylinder so that the piston just contacts the spring actuator
gives the curve shown in Figure 5c. Alternatively, preloading the spring and
setting the cylinder so that a gap is created between the piston and the spring
actuator gives the curve shown in Figure 5d. Spring adjustments can be done by
hand with the exception of preloading the spring, which requires an allen wrench
to hold the piston while the piston nut is tightened with a wrench. Threading a
Wootten and Hull
158
bolt into the spring assembly bracket can impede the motion of the spring
actuator, thus either reducing the range of rotation or locking the degree of
freedom at a set angle.
Calibration of Linear Motion Potentiometers
A calibration was performed to relate the output voltages from the linear motion
potentiometers to the pivot angles. Both potentiometers were calibrated over the
full range of motion of 10" permitted by each of the modules. In the case of
inversion/eversion, known angles were established by placing precision ground
steel angles on top of the convex cylinder and pivoting it until the top surface
of the steel angle was level. For the axial rotation potentiometer, known angles
were established similarly except that the axial rotation module was placed on
its side. To quantify the relations between the input angles and output voltages,
these data for each potentiometer were used in a linear regression to determine
the slope and intercept of the equation.
+
where V is the output voltage, b is the intercept, m is the slope, and @ is the input
angle. These data proved to be very linear with an R2 of 0.9999.
After the linear motion potentiometers were calibrated, an accuracy check
was conducted. The angles were set using the methods described for the
calibrations. The apparent angles were then calculated by solving the regression
equations. The maximum absolute difference of the calculated angles minus the
set angles was less than 0.2".
Sample Angle Data
Sample pedal angle data were collected to demonstrate the functions of the pedal
interface. The cleat and axes of rotation were arbitrarily set in a neutral position
with the cleat center located at a reference position of 6.35 cm lateral of the
crank and 3.0 cm directly above the spindle center. The axial rotation axis was
adjusted to pass through the cleat center and the inversion/eversion axis was
adjusted such that it intersected the axial rotation axis. The degrees of freedom
were allowed to free-float, without springs resisting the rotations. Data were
collected for three test conditions: both degrees of freedom allowed, the axial
axis locked in the middle of its range so that only inversion/eversion was allowed,
and the inversion/eversion axis locked in the middle of its range so that only
axial rotation was allowed. Axes were locked using screws in place of spring
assemblies.
The subject in this study was an experienced bicyclist who rode a racing
bicycle mounted on a Schwinn Velodyne stationary trainer at a cadence of
92 rpm and a power output of 200 Watts. The rider was given approximately
5 minutes to adapt to each test condition before crank angle, pedal angle, and
foottpedal interface angles were collected. Crank and pedal angles were measured
following the procedures described in Hull and Davis (1981). Ten crank revolutions were collected using a personal computer equipped with an analog-todigital conversion interface. Data were sampled at a rate of 300 Hzlchannel.
Footlpedal interface angles averaged over the 10 crank cycles are plotted
Design of a Foot/Pedal Interface
159
versus the crank angle in Figures 6 and 7. The crank angle is the angle of the
right crank viewed from a lateral position with clockwise (forward pedaling)
being positive from the 0" reference at top dead center. The vertical bars represent
the standard deviations over the 10 cycles.
When only axial rotation was allowed (Figure 6), the average forefoot
angle ranged from 0.8" of adduction to 1.2" of abduction with relatively large
standard deviations that ranged from 1.1 to 1.9". Because the bicyclist's forefoot
adducted on the downstroke and abducted on the upstroke with nearly equal
extreme values, the average axial angle was only slightly abducted. The average
axial rotation angle cycled once with every crank revolution.
In contrast to axial rotation in which the overall average axial rotation was
near O", the average inversion/eversion angle (Figure 6) remained everted and
ranged from 2.7" of eversion to 7.1" of eversion, with an overall average foot
position of approximately 4.5". Similar to the results for axial rotation, standard
deviations were relatively large, ranging from 1.8 to 2.8". Also, the average
inversion/eversion angle cycled once per crank revolution.
Comparing the data when both degrees of freedom were allowed (Figure
7) with data when only axial rotation was allowed and when only inversion1
eversion was allowed (Figure 6) shows the presence of interactions between the
two degrees of freedom. Although the curves for the same degree of freedom
have similar shapes when either one or two degrees of freedom were allowed,
the foot was more angled and had more angular motion when both degrees of
freedom were allowed. The overall average eversion angle increased from 4.5 to
7.5" and the overall average axial angle went from being nearly 0 to 1.4" of
+ adduction
Axial
Rotation
- abduction
+
inversion
Inversion/Eversion
-
eversion
Crank Angle (degrees)
Figure 6 - Degree of freedom angle vs. crank angle when degrees of freedom are
allowed individually. Averages over 10 crank cycles are plotted together with error
bars indicating +1 SD. The average peak forefoot angles in abduction/adductionwere
approximately equal so that the overall average rotation was nearly 0". The average
inversion/eversion angles were always everted.
Wootten and Hull
160
+
adduction
Axial
-
Rotation
abduction
+
inversion
InversionIEversion
-
0
60
120
180
240
300
eversion
360
Crank Angle (degrees)
Figure 7 - Degree of freedom angle vs. crank angle when both degrees of freedom
were allowed. Averages over 10 crank cycles are plotted together with error bars
indicating f1 SD. When both degrees of freedom were allowed, the overall averages
and ranges of average values changed from when degrees of freedom were allowed
individually, indicating interactions between the two degrees of freedom.
adduction. The range of average axial rotation angle increased from 2.0 to 2.8"
when inversion/eversion was allowed, while the range of average inversion1
eversion angle increased from 4.4 to 4.7" when axial rotation was allowed.
Of the two range increases, that of inversion/eversionrotation is comparable
to the measurement accuracy of the potentiometers. Accordingly, no significance
should be attached to this result. Note that although the standard deviations in
Figure 7 exceed the 10" limit of rotation, the extreme rotation actually measured
was only -9.7". Thus the limits of rotation were never achieved by this subject.
Discussion
Pedal Interface Design
The pedal interface designed is intended to be used as a research tool in the study
of overuse injuries to the knee in cycling. Because many factors may affect the
motion of the foot, and hence the loads developed at the knee joint, the pedal
interface was designed to allow these factors to be varied systematically so that
their effects might be investigated.
One factor was the degrees of freedom. The interface offers two degrees
of freedom, inversion/eversion and axial rotation, which can be used either
separately or together. Although these axes do not correspond with anatomical
axes, the interface will allow the foot to rotate about the anatomical axes while
attached to the pedal, provided that both degrees of freedom are permitted
simultaneously. The degrees of freedom can be permitted separately so that their
Design of a FooVPedal Interface
161
effects can be isolated and studied. Isolating the effects is desirable for determining
whether a simple footlpedal interface, with only a single degree of freedom,
results in reduced knee loads. However, it was necessary to include both
degrees of freedom to allow interactions between the degrees of freedom to be
investigated.
Another factor was the placement of the inversion/eversion and axial
rotation axes relative to the foot. If the placement of the pedal interface axes of
rotation coincides with the point of application of forces, then pivoting due to
moments caused by these forces will be minimized. Therefore it may be desirable
for the medialPatera1 and vertical placement of the inversion/eversion axis to
correspond with the intersection of the center of vertical pressure and the center
of medialPatera1pressure. This would minimize rotation due to these pedal forces
while allowing for rotation due to applied moments, such as the foot attempting
to rotate about the subtalar joint.
Accordingly, the interface allows the inversionleversion axis position to be
varied mediallyPaterally with respect to the foot so that the effect of this factor
on knee moments may be investigated. The elevation of this axis is not adjustable,
however, due to difficulties in designing an interface that permits changing the
elevation of this axis while maintaining a constant height of the shoe sole above
the pedal spindle. The elevation for this axis was chosen at the bottom of the
shoe because this was believed to be approximately the center of medialPatera1
pressure.
Axial rotation caused by forelaft and medialPatera1forces will be minimized
in a similar manner if the axial rotation axis is located at the intersection of these
two forces. Therefore the interface allows variation of the medialPatera1 and
forelaft placement of the axis relative to the foot. However, the location of the
applied loads may vary with crank angle and subject, making it impossible to
establish ideal axis positions.
Because the placement of the foot relative to the pedal spindle might
affect pedal loads and ultimately knee loads, the interface included means for
establishing a reference foot position once the axes are located. The reference
position used in the tests in which the sample data were collected established the
center of the cleat at a distance of 6.35 cm laterally from the crank, which is
approximately 1.3 cm directly above the pedal spindle center. The extra lateral
distance allows more axial rotation without the heel hitting the crank. The
extra distance also provides increased clearance to accommodate medialPatera1
adjustments should these be performed.
Because the elevation of the inversion/eversion axis cannot be adjusted in
the present design, the reference position of the height of the shoe sole is
established by the pedal dynamometer to which the interface attaches. An existing
dynamometer (unpublished) to which the interface was mounted for the tests
reported here established the height of the shoe bottom above the spindle center
to be 3.0 cm, which is 1.0 to 1.5 cm higher than that established by many pedals.
How the height affects results is unknown. Thus it would be desirable to connect
the interface to a dynamometer that either establishes a conventional height or
allows for height adjustment.
The amount of pivoting provided by each degree of freedom is k 10".
These limits were imposed by practical considerations. In the case of abduction/
adduction rotations, exceeding 10" abduction causes the medial malleolus to hit
162
Wootten and Hull
the crank arm in the upstroke. Inversion/eversion rotation is limited by the
inversion/eversion module rotating to the point where it bottoms out on the axial
rotation module below. Although the inversion1eversion limit can be controlled
through design, increasing the limit requires a compromise in height. To control
the height, the limit was set at k 10".
To investigate how different methods of applying restoring moments might
affect knee loads, spring assemblies were designed to provide the four loaddisplacement relations depicted in Figure 5. The ability of the spring assemblies
to provide these relations was confirmed through testing. The rationale behind
the relation in Figure 5a is that spring force that varies linearly with displacement
may be sufficient to reduce excessive pivoting. Permitting the foot to pivot until
it reaches a certain angle before applying a spring force (Figure 5b) may be
preferred if only a small amount of resistance is needed. Alternatively, it may
be beneficial to preload the spring (Figure 5c) if greater restoring force is needed.
Finally, the foot can also pivot freely until it reaches a certain angle before it
hits a preloaded spring (Figure 5d) for a smoother deceleration than just hitting
a stop. This would be useful for subjects whose natural motion would exceed the
limits of rotation.
In order to limit inertial effects caused by nonconstant angular crank
velocities, the weight of the interface was an important concern. Varying angular
crank velocity may be caused by noncircular chainrings, for example. A weight
of 0.65 kg for the combined modules was achieved by utilizing the high strength
and low density of 7075 T6 aluminum. The aluminum surfaces of the interface
were coated with Teflon-S for bearings that have low friction and wear with only
a slight increase in weight.
Of course the total weight of the interfaceldynamometer assembly will
depend on the weight of the dynamometer. A present dynamometer to which the
interface can mount also weighs 0.65 kg, giving a total weight of 1.30 kg.
Although this is about five times the weight of a typical pedal, test subjects do
not notice any effect when pedaling with noncircular chainrings.
Sample Results
To demonstrate the function of the pedal interface, an experiment was conducted
using a single subject who pedaled for three test conditions. Results of the
experiment showed that the interface performed as desired for all test conditions.
Rotations occurred smoothly without any evidence of either excess friction or
binding. For the subject tested, motions were within the allowed ranges of rotation
of 10". Hence the data collected appear to be a reasonable representation of
the motions the foot would naturally undergo for each of the three test conditions.
Because the interface performed as desired in permitting natural movement
of the foot, it is worth discussing some of the key observations from the sample
data. One is the relatively large standard deviations. Although the subject
was an experienced cyclist, these standard deviations indicate between-cycle
inconsistencies in the subject's pedaling mechanics. It is possible that, through
increased adaptation time in using the equipment, these standard deviations would
diminish.
The sample results were remarkably different than expected. It was hypothesized that the bicyclist would pronate during the power phase. As the crank was
+
Design of a FootIPedal Interface
163
pushed down, the foot was expected to plantarflex, abduct, and evert (Francis,
1986). However, the sample results showed that the bicyclist's forefoot adducted
(i.e., moved from being ab- to ad-ducted) and everted on the average during the
power phase, which is not congruent with the normal motions of the foot and
ankle (Root, Orien, & Weed, 1977). This unexpected motion of the foot could
be a result of joint motion of the hip and knee as well as the ankle and foot, all
of which act in concert to allow for adduction and eversion simultaneously. To
explain this unexpected motion, it would be useful to monitor the kinematics of
all joints in the chain.
More motion was observed when both degrees of freedom were allowed
simultaneously than when only a single degree of freedom was allowed. This
could be due to the increased mobility of the ankle and foot joints as pronation
and supination are allowed. The axes of the ankle and foot are all triplanar axes
and any attempt to produce motion in only one plane will sublux and jam the
joint (Root et al., 1977). Not allowing all three axes would reduce triplanar
motion and load the joints. This interaction implies that footlpedal interfaces
must include both degrees of freedom together to obtain accurate results pertinent
to such interfaces. Studying each degree of freedom separately and superimposing
the results would ignore these interactions and give misleading results. It is likely
that interactions will be found in the loads as well as the motions.
Conclusion
The goal of this project was to design a pedal interface that allows the systematic
variation of a number of factors that potentially affect loads transmitted by the
knee joint and hence overuse injuries to this joint. A pedal interface was designed
in three modules-the cleat connector, the inversion/eversion module, and the
axial rotation module-which allow the foot f 10" of inversion/eversion and
axial rotation. These degrees of freedom can be implemented either separately
or together. The pedal interface allows the foot to be located in a reference
position and the placement of the axes to be adjusted relative to this position.
There are four spring configurations available to resist rotation.
Sample pedal interface angle data were collected that demonstrate the
functionality of the interface. With no spring resistance, the interface allowed
free movement of the foot without excessive friction and within the 10"ranges
permitted. Demonstrating an apparent significant interaction between the two
degrees of freedom, angular motion increased when both degrees of freedom
were allowed simultaneously compared to the motion occurring when each degree
of freedom was allowed separately. Consequently, with its multi-degree-offreedom capability in addition to the many other design features, and with its
demonstrated functionality, the interface in conjunction with an appropriate
dynamometer and motion analysis system should provide the necessary instrumentation for investigating the effects of the various factors on knee loads.
+
References
Francis, P.R. (1986). Injury prevention for cyclists: A biomechanical approach. In E.R.
Burke (Ed.), Science of cycling (pp. 145-184). Champaign, IL: Human Kinetics.
Francis, P.R. (1988). Pathomechanics of the lower extremity in cycling. In E.R. Burke
Wootten and Hull
(Ed.), Medical and scientific aspects of cycling (pp. 3-16). Champaign, IL: Human
Kinetics.
Gaston, E.A. (1977, November). Biker's knees. Bicycling.
Hannaford, D.R., Moran, G.T., & Hlavac, H.F. (1986). Video analysis and treatment of
overuse knee injury in cycling: A limited clinical study. Clinics in Podiatric
Medicine and Surgery, 3, 671-678.
Hull, M.L., & Davis, R.R. (1981). Measurement of pedal loading in bicycling: I.
Instrumentation. Journal of Biomechanics, 14, 843-855.
Pruitt, A.L. (1988). The cyclist's knee: Anatomical and biomechanical considerations. In
E.R. Burke (Ed.), Medical and scientific aspects of cycling (pp. 17-24). Champaign,
IL: Human Kinetics.
Root, M.L., Orien, W.P., & Weed, J.H. (1977). Clinical biomechanics-Volume [I, Normal
and abnormal function of the foot. Los Angeles: Clinical Biomechanics Corp.
Ruby, T., Hull, M.L., & Hawkins, D. (1992). Three dimensional knee loading during
seated cycling. Journal of Biomechanics, 25, 41-53.
Zahradnik, F, (1990, July). Pivotal issue; Should your feet be fixed or floating? Bicycling,
pp. 134-137.
Acknowledgments
We are grateful to the Shimano Corporation of Osaka, Japan, and Shimano American
Corporation for providing the financial support for this project. We also thank Don Barnum
of Mechanical General Services in the College of Engineering at UC-Davis for his
excellent fabrication of the footlpedal interface.