Relationship between individual hip extensor muscle size and sprint running performance: sprint phase dependence.

The muscle size of the hip extensors has been suggested to be important in sprint running performance; however, reported findings are partly inconsistent. Here, we hypothesised that the association between hip extensor size and sprint performance may vary by sprint phase (early-acceleration, maximal-velocity and deceleration phases). To test this hypothesis, we measured the volumes of individual hip extensors of 26 male sprinters via magnetic resonance imaging and their sprint velocities for each 10-m interval during a maximal-effort 100-m sprint. Based on the sprint velocities, the maximal-velocity phase was determined for each sprinter. At the individual muscle level, the semimembranosus volume relative to body mass was positively correlated with sprint velocity only in the early-acceleration phase (0-10 m,  = 0.592, corrected  = 0.003). On the other hand, the semitendinosus volume relative to body mass was positively correlated with sprint velocities in the maximal-velocity ( = 0.483, corrected  = 0.020) and deceleration (90-100 m,  = 0.605, corrected  = 0.003) phases. These results show that the association between hip extensor size and sprint performance is not constant but changes through the sprint phases.