FORCE PLATE LAB
EXPERIMENTAL DESIGN ex. compare walking to running, compare changes in horizontal impulse,
compare different running speeds, compare shoes, compare ankle or foot taping methods.
PURPOSE
The purpose of this study was to describe the variability ground reaction forces during
running.
METHODS
DATA COLLECTION
Vertical, anterior-posterior and medial-lateral ground reaction forces were measured for
a __ kg subject running at __ m/s and running at __ m/s using a AMTI Model OR6-7-1000
(Watertown, MA) force plate and an AMTI MSA-6 amplifier interfaced to a Dell computer. The
AMTI OR6-7-1000 has a 4450 N capacity for Fz and a 2225 N capacity for Fx and Fy. The Fz
channel has a natural frequency of 480 Hz and Fx and Fy have a natural frequency of 300 Hz. The
platform was installed flush with a 3 m unobstructed running surface. Only trials in which the
force platform contact were made with a smooth, unbroken stride were retained for analysis.
Running speed was not controlled; instead it was self-selected by the subject. No attempt was
made to control for shoe type. All subjects wore the shoes they customarily used for running.
The force data were sampled at 1000 Hz using a National Instruments (Austin, TX) PCI-6229, 16bit analog-to-digital converter.
An analog comparator of 6 N was used to identify the start and end of ground contact
(1, 2). The force data were filtered with a Butterworth 4th order recursive low pass digital filter
at 200 Hz. After data collection was completed, the change in velocity of the center of mass in
the anterior/posterior direction during force plate contact was calculated using the following
linear impulse-momentum relationship:
 Fy(t )  mVy
f
 mVyi
where Fy is the anterior-posterior
force, m is mass, and Vy is the
horizontal velocity of the center
of mass. Trials in which the
change in velocity in the
anterior/posterior direction was
greater than  0.10 m/s were
rejected. The following variables
were calculated: impact force,
time to peak impact force, loading
rate, braking impulse, propulsion
impulse, contact time, change in
vertical velocity, and change in
horizontal velocity. Loading rate
was calculated by computing the
rate of change in force in BW
from 50 N to BW + 50 N.
Results
Describe the shape of the curves. Give the magnitudes and time to magnitudes in BW. For
example: The A/P force showed two braking phases. The first phase reached a peak of −.5 BW
at 27 ms and the second peak reached a magnitude of .6 BW at 79 ms. Midstance occurred at
147 ms as the runner shifted from braking to propulsion. Include Figures of vertical and
anterior/posterior force time graphs to show differences between your experimental
conditions.
Discussion
Compare the results of your
experiment to the data of
Cavanagh et al. and Munro et
al. where applicable.
References
1.
2.
Cavanagh PR, and Lafortune MA. Ground reaction forces in distance running. J Biomech
13: 397-406, 1980.
Munro CF, Miller DI, and Fuglevand AJ. Ground reaction forces in running: A
reexamination. J Biomech 20: 147-155, 1987.
Center of Pressure Calculations for Force Plate
ZoffPlate1 = -0.040238
Xcop = 100 * (( My + ( ZoffPlate1 * Fx ) ) / Fz ) ' in cm
Ycop = 100 * (( Mx1 − ( ZoffPlate1 * Fy ) ) / Fz )
+25.4
+25.4cm
cm
+Y
(0, 0)
+X
−25.4 cm
−23.2 cm
+23.2 cm