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 (K-leg), the normalized effective vertical stiffness (K-vert), and the mass-specific mechanical power output of the spring (P-sp) 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.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 K-leg (r = -0.18), an inverse relationship between aerobic demand and K-vert (t = -0.48), and a positive correlation between aerobic demand and P-sp (r = 0.45). Conclusions: The inverse relationship between K-vert 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.