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rkram94
05-24-2007, 09:54 AM
Li Li raises an interesting point and he proposes a way to test it.

But, a study by Peter Weyand et al. suggests that
minimizing contact time and not swing time is the
key variable to consider.
I really like Peter's study, not everybody feels
that his inferences are correct.
abstract and free pdf link pasted below.

Rodger Kram

J Appl Physiol 89: 1991-1999, 2000;

Faster top running speeds are achieved with
greater ground forces not more rapid leg movements
Peter G. Weyand, Deborah B. Sternlight, Matthew J. Bellizzi, and Seth Wright

Concord Field Station, Museum of Comparative
Zoology, Harvard University, Bedford,
Massachusetts 01730

We twice tested the hypothesis that top running
speeds are determined by the amount of force
applied to the ground rather than how rapidly
limbs are repositioned in the air. First, we
compared the mechanics of 33 subjects of
different sprinting abilities running at their
top speeds on a level treadmill. Second, we
compared the mechanics of declined (6) and
inclined (+9) top-speed treadmill running in
five subjects. For both tests, we used a
treadmill-mounted force plate to measure the time
between stance periods of the same foot (swing
time, tsw) and the force applied to the running
surface at top speed. To obtain the force
relevant for speed, the force applied normal to
the ground was divided by the weight of the body
(Wb) and averaged over the period of foot-ground
contact (Favge/Wb). The top speeds of the
33 subjects who completed the level treadmill
protocol spanned a 1.8-fold range from 6.2 to
11.1 m/s. Among these subjects, the regression of
Favge/Wb on top speed indicated that this force
was 1.26 times greater for a runner with a top
speed of 11.1 vs. 6.2 m/s. In contrast, the time
taken to swing the limb into position for the
next step (tsw) did not vary (P = 0.18). Declined
and inclined top speeds differed by 1.4-fold
(9.96 0.3 vs. 7.10 0.3 m/s, respectively),
with the faster declined top speeds being
achieved with mass-specific support forces that
were 1.3 times greater (2.30 0.06 vs.
1.76 0.04 Favge/ Wb) and minimum tsw that were
similar (+8%). We conclude that human runners
reach faster top speeds not by repositioning
their limbs more rapidly in the air, but by
applying greater support forces to the ground.


http://jap.physiology.org/cgi/reprint/89/5/1991?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&author1=Weyand&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT