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 ( SI(MT)), ankle musculoarticular active ( SI(MA)) and passive ( K(P)) stiffness. Leg-spring stiffness ( K(leg)) was measured during vertical hopping. Runners and gymnasts presented significantly higher SI(MT) 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 SI (MT) 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.