Sunday, 6 June 2010

Touch and Go #6

Posted by speedygeoff on Sunday, June 06, 2010 with No comments
Barefoot/Forefoot runners have a “smoother” ride: Difference in collision forces:
Barefoot runners “take shorter strides and to run with greater vertical leg and ankle compliance (the lowering of the body’s centre of mass relative to the force of the impact). This serves to blunt the transient force and results in a less jarring, ‘smoother ride’.” (Jungers, 2010)

Basically this means that because of the footstrike difference, the body uses the lower leg in a more efficient shock absorbing way. The foot is more plantar flexed and the ankle is more compliant. This creates a situation where the collision is essentially absorbed and spread out better.

In heel striking the collision forces are concentrated in one area, and very sudden. Meaning a large amount of force in one place, very quickly. Meanwhile in a more flat footstrike, as mentioned above, the impact is spread out, absorbed better, and not so sudden. This leads to peak vertical forces 3x lower in barefoot vs. shoe wearing runners and a rate of loading that is half as much for barefoot compared to shoe wearing runners

This difference may lead to injury prevention, as some studies have suggested that it’s not necessarily the total impact forces but the high rate of force in a very short time. (Look at the drawings in my article below and remember that barefoot running doesn’t have the initial peak impact force). Still, the impact force debate can be VERY misleading. Just a word of caution to read my other blog post on running shoes and realize that peak impact forces do not relate to injuries

Concrete vs. Dirt:
Another interesting finding is the adjustment of impact forces that occurs based on the ground you are going to strike. The study found that barefoot running produced less collision forces on a hard surface than a cushioned shoe.

Similar to the conclusions I came to in the Running shoe article (see Steve’s blog), they found that leg stiffness was adjusted to control impact. This created a situation where there was no difference in rate or magnitude of impact loading based on the surface they were running on. As I have said many times, the body has a built in adjustment mechanism. It controls impact via adjustment of several different mechanisms.

So all those people who are worried about the impact forces of running barefoot on concrete should consider that when they stick a cushioning shoe on and heelstrike, there collision forces are higher!

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



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