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lli92
05-25-2007, 02:38 AM
Thanks to Rodger Kram for pointing out the Weyand et al. (2000) study. Sorry
that I did not mention it.

I had my reasons. Pistorius changes his prosthesis whenever he prepares to
sprint. The subjects in Peter's study cannot modify their limb mass. But, in
their discussion section, they did state that "Although equivalent maximal
stride frequencies do not explain the different top speeds achieved during
declined and inclined running, they do provide additional evidence that a
constraint on minimum swing times limits the top speeds of human runners."
So, I think that significant differences in limb masses might, just might,
provide us with big enough difference among the two populations. After all,
"the swing period comprises three-fourths of the total stride time at top
speed," Weyand et al. (2000).

I also like Peter's study, but I also believe that we should not have our
fondness of the paper to prevent us in seeking the relevant evidences.

I have tried to study the video clips that I got from Googling (?), but
failed miserably. The resolution of the clips that I could find were not
good enough to estimate accelerations.

So, does anyone has the data to show us the magnitude of Oscar Pistorius'
angular hip acceleration during the initiation of the swing phase?


Li Li, Ph.D.
Department of Kinesiology
Louisiana State University
112 Long Field House
Baton Rouge, LA 70803
225-578-9146 (phone)
225-578-3680 (Fax)
lli3@lsu.edu

On 5/24/07, Rodger Kram wrote:
>
> 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
>
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