Abstract

A model of running is proposed in which the leg is represented as a rack-andpinion element in series with a damped spring. The rack-and-pinion element emphasizes the role of descending commands, while the damped spring representsthe dynamic properties of muscle and the position and the rate sensitivity of reflexes. This model is used to predict separately the effect of track compliance on step length and ground contact time. The predictions are compared with experiments in which athletes ran over tracks of controlled spring stiffness. A sharp spike in foot force up to 5 times body weight was found on hard surfaces, but this spike disappeared as the athletes ran on soft experimental tracks. Both ground contact time and step length increased on very compliant surfaces, leading to moderately reduced running speeds, but a range of track stiffness was discovered which actually enhances speed. Verf.-Referat