Relationship between the morphological and mechanical properties of muscle-tendon units and sprint performance in prepubescent sprinters

This study aimed to examine the relationship between the morphological and mechanical properties of the muscle-tendon unit and sprint time in prepubescent sprinters. Fifteen prepubescent sprinters participated in this study; the average personal best time in a 100 m race was 14.00 ± 0.68 seconds. The stiffness of the tendon structure was measured using ultrasonography during isometric contraction; the muscle thickness of the vastus lateralis (VL) and the medial gastrocnemius (MG) were also measured. There was a significant negative correlation between tendon structure stiffness of the plantar flexors and 100 m personal best time (r = −0.58, P < 0.05), but not the knee extensors. Unlike for the MG, the muscle thickness of the VL (r = −0.61, P < 0.05) and the 100 m personal best time were significantly negatively correlated. Stepwise regression analysis identified the tendon structure stiffness of the plantar flexors and the muscle thickness of the VL as independent variables, which were significantly associated with the 100 m personal best time (r = 0.77, P < 0.01). These results suggest that in prepubescent sprinters, superior sprint performance is induced by a stiff tendon structure of the plantar flexors and a greater muscle thickness of the VL.