Muscles excite and synchronize themselves through body dynamics

Abstract

In this study, we constructed a minimal model to clarify the role of the animal body and motor neurons in the generation of synchronized periodic motions. The novel contribution of this study is the analysis of the phenomenon of adaptive muscle synchronization that occurs only by inter-muscular interaction through the body dynamics. The proposed model is based on the primitive local feedback in animal muscles, which is called the stretch reflex. We conducted theoretical analysis and simulations using a single muscle model and its combinations (an antagonistic muscle pair and a limb model). The results of the theoretical analysis revealed the necessary and sufficient condition for limit cycle generation with resonance frequencies. Without any explicit neural connection between the muscle modules, the proposed simple model suggests that musculoskeletal systems can automatically generate resonant oscillation. Moreover, the resonance behavior is adaptive to changes in the body parameters of these systems.