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Talk Abstract
Symmetry, Asymmetry, Bifurcations and Intention in Human Locomotion

Institute for Mathematics and Its Applications
Jill Whitall, University of Maryland-Baltimore

In the case of bipedal walking, the adoption of a symmetrical anti-phase relationship between the legs is supported from a mechanical modeling perspective. The robustness of this solution is seen in its ready adoption by newly walking infants. However, walking per se is rather limiting as the only mode of locomotion and infants soon learn to be more adaptable in their environment by acquiring other forms such as running (also symmetrical and anti-phase) and galloping (asymmetrical). In the first half of the talk I will discuss characteristics of these gaits both as steady state behaviors and when taken through speed-related transitions. Kinematic and kinetic descriptions of these gait patterns will be related to the properties of coupled nonlinear oscillatory systems. In particular, I will concentrate on the bipedal gallop which, unlike the gallop of quadrupeds, appears to be almost always initiated with the ``intention'' of changing the phasing relationship between the legs.

The second half of the talk also will address the interface of intention with gait, but in this case the focus will be on humans who crawl on their hands and feet to purposefully adopt quadrupedal gait form. Rather than requiring them to change phasing, we asked for a change of direction (forwards/backwards) and postural orientation (prone/supine). The resulting consequences to their coordination (phasing) reflected both mechanical and non-mechanical influences. Overall it is suggested that mechanical constraints have a powerful influence on human locomotion patterns, but they provide only a part of the picture with respect to how the interlimb coordination emerges. The general theme across both sets of data is to question whether the existing models of animal locomotion can accommodate these data, and/or suggest that models seeking to represent (human) gait should incorporate intentional variables along with the necessary mechanical/dynamical variables.

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