Abstract
To determine the effects of widely varying amounts of cushioning upon vertical force
(VF) parameters, ten male subjects, (mean weight = 68.0 kg) ran at a speed of 4.5
m·s-1 (6 min/mile pace) and contacted a Kistler force platform. Two shoes were tested:
a hard one and a softer shoe that had 50% more cushioning as measured by an instrumented
impact tester. Five right footfalls were collected for each shoe on each subject during
which the ground reaction forces were sampled at 500 HZ using a PDP 11/34 minicomputer.
Eight parameters from the VF data obtained for each trial were selected for analysis
and compared statistically using a paired difference t test. It was found [force magnitudes expressed in multiples of body weight (BW)]
that the time to the vertical force impact peak (VFIP) was significantly longer (hard
= 22.5 ms, soft = 26.6 ms) in the soft shoe; however, no differences were seen in
the magnitudes (hard = 2.30 BW, soft = 2.34 BW). The minimum after the VFIP was also
significantly delayed in the soft shoe (hard = 33.8 ms, soft = 37.9 ms) and was significantly
greater in the soft shoe (hard = 1.46 BW, soft = 1.90 BW). The peak VF propulsive
force occurred statistically at the same time in both shoes (hard = 85.7 ms, soft
= 84.0 ms), but was significantly greater in the soft shoe (hard = 2.73 BW, soft =
2.83 BW). No significant differences were found for total contact time (hard = 227.
ms, soft = 223. ms) and the total VF impulse (hard = 0.354 BW·s, soft = 0.357 BW·s).
This study provides evidence that certain VF parameters vary depending upon the footwear
used and that these differences can be measured by a force platform. Discussion of
these results will center upon the mechanical and adaptive responses of the runners
to varied shoe cushioning.
Key words
biomechanics - running - ground reaction forces and footwear
