More on the effects of gravitational torque

Earlier today I posted to say that my calculations indicated that the contribution of gravitational torque to running was minimal. Since then I have been engaged in an interesting discussion with Mike Stone (which you can see in the comments section at the bottom of the calculation page.) He initially challenged one of the mathematical steps in my calculation, but I think we have agreed that subject to the validity of the assumptions on which my calculations were made, that is OK. However, he is currently querying the assumptions.

My understanding of the situation is that the calculation I have done gives a reasonable good estimate of the effect of gravitational torque if the assumptions are correct. The most important of these assumptions is the assumption that the ankle, hip and shoulder remain in a straight line. This was one of the rules for good Pose running originally specified by Dr Romanov, but there is no doubt that in practice runners disobey this rule once the pace has increased beyond a fast jog. What actually happens is that the hip extends while the runner is on stance so that the leg on stance rotates through a larger angle than the torso. To do the calculation in a more realistic way, we need to treat the body as consisting of at least two elements joined by a hinge at the hips to allow for the fact that at speed, runners do flex (backwards) at the hips. This calculation could be done, but will require more complex mathematical procedures. The flexion results in the COG moving relative to the hips while the runner is on stance

So where have we got to: I still think that provided the line from the ankle to the COG at lift off from stance leans by no more than about 10 degrees, the contribution of gravitational torque to running is likely to be very small. However, there is no doubt that it would be best to do the calculation using a model in which the body is allowed to hinge at the hips. I hope that we can get this done in the not too distant future.

 

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