Optimization of bi-articular muscle forces when going over obstacles during locomotion

A numerical optimization approach is used to investigate muscle force contributions required for the limb trajectory to successfully clear an obstacle during locomotion. A direct search optimization method was applied to a four degree-of-freedom link-segment model of the swing limb. The initial conditions and muscle force profiles were optimised to achieve specific trajectory characteristics. It was found that a high initial angular velocity of the hip was required to obtain the desired toe trajectory. This, and the observed knee trajectory, suggest that hip hiking and/or single joint muscle forces are important when stepping over obstacles.