Modeling muscle cross-bridge dynamics for movement simulations

Muscles have transient and history-dependent properties that may be important in dynamic and unpredictable interactions with the environment, such as running on uneven terrain. Hill-type muscle models do not model a variety of phenomena emergent from acto-myosin interactions, such as short-range stiffness that transiently increases the resistance of the muscle to externally imposed stretch. We developed a Matlab-based 2-state model of cross-bridge kinetics within a half-sarcomere. As a first step, we verified that the steady state properties (i.e. force-length and force-velocity relationships) generated by the model are similar to those measured experimentally. Our simulated half-sarcomere can be integrated into existing musculoskeletal simulations, using the same inputs as the contractile element of a Hill model. Simulating cross-bridge dynamics within muscle-tendon units may be critical to understanding the role of intrinsic muscle properties in highly dynamic and robust movements.