Friday, 11 June 2010

Touch and Go #11

Posted by speedygeoff on Friday, June 11, 2010 with No comments
Ground contact time and footstrike related to running speed. What it all means:
What does this all mean? It’s hard to make a lot of conclusions since the hard data on the British studies could not be evaluated yet. The preliminary observations are very interesting though.

In regards to foot strike, there is a relationship between running speed and footstrike. Do all fast runners forefoot strike? No, but there is a tendency for the faster runners to forefoot/midfoot strike more so than the slower runners.

Is this a function solely of the speed that they are running? Speed of running certainly plays a role in where you strike to an extent but it’s unlikely that it plays as much of a role as people make it out to. Meaning that someone is not going from a straight heel strike while running easy to a forefoot strike while running 800m pace. The Lieberman study provided the first evidence showing that forefoot strikers struck forefoot regardless of condition. Similarly, if we look at the data in the studies above, you can see that the percentage of footstrike types is remarkably similar despite the significant increase in average running speed (from 63-64sec per lap down to 57.5sec per lap). Even though these are different people running each event, if foot strike was solely a function of speed, like many have claimed, then you would expect to see a definite trend away from heel striking as the group got faster.

Fatigue:
Perhaps most interesting is what seems to happen during fatigue. Ground contact times increase in both studies, regardless of footstrike. If we look back at what typically impacts ground contact time, it provides some interesting clues. Ground contact changed even when footstrike did not, so we can eliminate that possibility. The other two possibilities are that leg stiffness and use of elastic energy changed, which is entirely possible, but impossible to know. There is some research showing fatigue changes leg stiffness and stretch shortening cycle fatigue. Lastly, the most likely scenario is that fatigue is impacting the body’s ability to produce force in as short a time period.

Lastly, in the 1500m study it was interesting to see a change in footstrike pattern. During the last lap, you saw an increase in heel striking. This would seem surprising as generally one of the faster laps in the race as people try and kick it in. The question is why do runners switch to a heel strike under heavy fatigue? I’m not sure I have the answer. One possibility is that stride length tends to decrease with fatigue and runners are trying to compensate by lengthening their stride, but instead of doing it by pushing off and covering more distance, they simply let their lower leg reach out. Another possibility is that fatigue may impact fine control of the lower leg.

from Science of Running by Steve Magness. To be continued...

Michelle

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