To describe the stretch-shortening behavior of ankle plantar-flexing muscle–tendon units (MTUs) during the push-off in a sprint start.
Fifty-four male (100-m personal best: 9.58–12.07 s) and 34 female (100-m personal best: 11.05–14.00 s) sprinters were analyzed using an instrumented starting block and 2-dimensional high-speed video imaging. Analysis was performed separately for front and rear legs, while accounting for block obliquities and performance levels.
The results showed clear signs of a dorsiflexion in the upper ankle joint (front block 15.8° ± 7.4°, 95% CI 13.2–18.2°; rear block 8.0° ± 5.7°, 95% CI 6.4–9.7°) preceding plantar flexion. When observed in their natural block settings, the athletes’ block obliquity did not significantly affect push-off characteristics. It seems that the stretch-shortening-cycle-like motion of the soleus MTU has an enhancing influence on push-off force generation.
This study provides the first systematic observation of ankle-joint stretch-shortening behavior for sprinters of a wide range of performance levels. The findings highlight the importance of reactive-type training for the improvement of starting performance. Nonetheless, future studies need to resolve the independent contributions of tendinous and muscle-fascicle structures to overall MTU performance.