Leg stiffness during hopping does not change with aging

Abstract

Purpose: During hopping, jumping and running, the musculoskeletal structure of the legs is often modelled with a spring-mass model, which consists of a body mass and a linear leg spring supporting the body mass 1. In the model, the stiffness of the leg spring (leg stiffness; K leg) is thought to be an important factor in musculoskeletal performance 2. However, despite the fact that many athlete's activities are often measured, little is known about the regulation of K leg in the elderly. Therefore, the purpose of the present study was to compare the K leg between the elderly and young subjects in a range of hopping frequency. Method: Fourteen elderly and eleven young subjects performed in-place hopping, matching metronome beats at 2.2, 2.6 and 3.0Hz. Based on the spring-mass model, K leg was calculated as the ratio of maximum ground reaction force to maximum center of mass displacement at the midstance (Figure 1). Results & Discussion: In both groups, the K leg increased with an increase in hopping frequency, but was not significantly different between groups (Figure 2). Statistical analysis revealed the existence of a significant main effect of hopping frequency on K leg. However, main effect of groups and interaction on K leg were not observed. The results of the present study indicate that leg stiffness during hopping is invariant with aging. Since too high or too low K leg is associated with musculoskeletal injury 2, footwear and/or surface materials, impact on K leg 2 should be considered for athletic environment in both master and young athletes.