Exploring The Role of Thigh Muscle Coordination with Biarticular Muscles for Stable Running

Abstract Legged animals including humans appear to efficiently exploit their elastic muscle coordination to achieve stable locomotion. Previous studies have shown that the elasticity of the leg realizes stable locomotion through the simple models comprising a mass and spring, and explained the stability of fundamental dynamics in human locomotion successfully. However, these models are excessively simple for interpreting the role of muscle coordination and implement on real systems. Thus, this study developed an analytical legged model to determine the role of muscle coordination in stabilizing biped running. In particular, we investigated the manner in which the thigh biarticular elastic mechanical elements aid in the stabilization of the torso pitch angle. We propose the torso-thigh muscle coordination (T-Tmc) model. The T-Tmc model was composed of the torso and three-pair of six-muscle structure in the thigh. We empirically showed that the T-Tmc model has the self-stability and generate a stable running without online input design. Further, the stable parameter region of the proposed model was investigated through numerical simulations and we found that the stable regions appear by setting the parameters appropriately. The T-Tmc model suggests how each muscle is coordinated in human locomotion.