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dferris43
08-01-2007, 12:20 PM
David,

Another follow-up on the question. If you believe that humans walk similarly to passive dynamic walking models (such as those studied by McGeer, Kuo, and Ruina), then a decrease in trailing limb pushoff from plantar flexion should also lead to an increase in the leading limb impact force. This leading limb impact force would come from heel strike. Thus, it could be not just that the push off is less, but that the heel impact could be higher as a result. See Kuo, Donelan, and Ruina (2005) Energetic consequences of walking like an inverted pendulum: step-to-step transitions. Exerc Sport Sci Rev, 33(2):88-97, for more details.

Incidentally, I have some unpublished vertical ground reaction force data on subjects with clinically complete spinal cord injury undergoing locomotor training with bodyweight support and manual assistance that really highlights this effect. The magnitude of the loading first peak was very large and the pushoff second peak was virtually nonexistent. It was very curious to us at first but seems to make much more sense in retrospect.

df


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Dan Ferris, Ph.D.

Human Neuromechanics Laboratory

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Dan Ferris

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