Intrinsic Ankle and Hopping Leg-Spring Stiffness in Distance Runners and Aerobic Gymnasts

The objective of this study was to examine the contribution of intrinsic ankle stiffness to leg-spring stiffness in high level athletes using various musculotendinous solicitations. 8 aerobic gymnasts (G), 10 long-distance runners (R) and 7 controls (C) were evaluated using quick-release and sinusoidal perturbation tests in order to quantify their respective plantarflexor musculotendinous (SIMT), ankle musculoarticular active (SIMA) and passive (K-P) stiffness. Leg-spring stiffness (K-leg) was measured during vertical hopping. Runners and gymnasts presented significantly higher SIMT values (P<0.01) than controls: 60.4 (+/- 14.1) rad(-1).kg(2/3) for G, 72.7 (+/- 23.8) rad(-1).kg(2/3) for R and 38.8 (+/- 6.5) for C. In addition, normalized K-leg was not significantly different between G, R and C. It appeared that intrinsic ankle stiffness had no influence on leg-spring stiffness. The adaptation of SIMT seems to concern specifically the active part of the series elastic component in runners. The results suggested that the number of stretch-shortening cycles during daily practice sessions, rather than their intensity, act as the determinant for this component.