Proprioceptive feedback in running?

Most studies addressing local feedback mechanisms are focused on posture and walking but only little is known about their role in fast locomotion. Some experimental studies on humans indicate a decrease in the activity of sensory signals with increasing speed (Collins et al. 1998, Simonsen and Dyhre-Poulsen 1999). It seems to be generally accepted that in fast movements the dynamics of the musculo-skeletal system dominate the system behavior. However, there is no explanation for the uniform spring-like leg operation used by many animals at different running gaits. In this study we address to what extend single muscle reflex loops can facilitate fast locomotion. Using a simple neuro-musculo-skeletal model we investigate the potential role of muscle reflexes in generating the spring-like leg behavior as observed in fast animal and human locomotion (Cavagna et al. 1964, 1977).