Meeting Abstract

115.1  Monday, Jan. 7  Torques in running and feet in walking – how deviations from point mass models give insight into bipedal locomotion HUBEL, T.Y.*; USHERWOOD, J.R.; Royal Veterinary College; Royal Veterinary College thubel@rvc.ac.uk

Reductionist point mass models are useful in understanding the underlying mechanical principles of walking and running. However, they are inevitably incomplete representations of true animal gaits. Exploring simple deviations from the point mass model can be give useful insights into human locomotion. Here we consider the implication of two small deviations from pure point mass models. In walking, foot structure and function deviates considerably from the point-foot assumption of point-mass compass-gait models. We suggest that the human heel-sole-toe stance during walking, and the structure of the lower limb, allows calf and shin muscles to be loaded when needed but largely unloaded during the passive vaulting phase, reducing the energetic costs of opposing isometric forces. While power is not, fundamentally, required to provide isometric force, the metabolic costs of resisting forces with muscle can be considerable, and the human foot provides a mechanism for limiting this cost. In running, the ground reaction forces pass close to the center of mass; pitching torques and motions are small. However, sending the GRF through the CoM comes at a price: the resulting fore-aft forces require mechanical and muscular work. Humans actually run with measurable – albeit small – torques, with GRFs missing the CoM. This allows a near-optimal compromise between reducing kinetic energy fluctuations and avoiding spinning, but is only possible because we are not point masses. While “torque-based” energy savings are small in humans, other animals such as kangaroos with their peculiar long-head/long-tail structure could benefit considerably from a non-zero-CoM-torque strategy.