Meeting Abstract
Bipedal runners, when changing their speed, can theoretically choose many combinations of stride length (SL), stride frequency (SF) and duty factor (DF). We seek a theoretical framework to predict the combination of SL, SF and DF used by individual species for a given speed. Previous work has been successful in using math models combined with optimal control methods to predict locomotion features by minimizing energy cost. For instance, a prior model showed that work-optimal control of a damped-spring-mass leg model could predict the asymmetrical stance dynamics of ground-running birds. This work builds atop the previous model by exploring additional physiologically relevant control constraints and mechanical components for the model; this is an attempt test plausible incentives for bipeds to change duty factors with speed. We systematically modeled the effects of power limits, force limits, and kinematic limits on optimal gait duty factor, and all of which found a grounded gait (DF=0.5) to be energetically optimal regardless of speed. However, including an inertia-based cost to leg swing and minimizing mechanical COT yielded a decreasing duty factor with speed- similar to bipedal animals. This work further compared these model predictions to the experimental duty factors of helmeted guinea fowl (Numida meleagris) during steady running across speeds. By fitting the three free model parameters (spring stiffness, damping constant, and leg inertia), the mathematical prediction matched the SL, SF, and DF of our guinea fowl data set from 1.3m/s up to 3.1 m/s running. We aim to use this model to further predict bipedal locomotion features such as gait transitions and gait adaptations to non-rigid terrain.
