???Leg spring??? characteristics and the aerobic demand of running

PURPOSE: By applying a simple, linear mass-spring model to running, the normalized leg spring stiffness (Kleg), the normalized effective vertical stiffness (Kvert), and the mass-specific mechanical power output of the spring (Psp) were determined and correlated with aerobic demand. The purpose of the study was to determine whether leg spring characteristics explain any of the interindividual variability observed in aerobic demand at a given submaximal running speed. METHODS: Recreational runners (N = 16) ran on a treadmill at 3.35 m x s(-1) for physiological measures and overground for biomechanical measures. The latter included a sagittal plane video record of the running motion and ground reaction data. RESULTS: We found no relationship between the aerobic demand of running and Kleg (r = -0.18), an inverse relationship between aerobic demand and Kvert (r = -0.48), and a positive correlation between aerobic demand and Psp (r = 0.45). CONCLUSIONS: The inverse relationship between Kvert and aerobic demand indicates that less economical runners possess a more compliant running style during ground contact. This running style may place greater force demands on extensor musculature.