Differences in Hamstring Muscle-Tendon Unit Geometry and Function Between Elite Sprint and Jump Athletes and Recreationally Active Controls.

The hamstrings are critical for athletic performance; however, no study has examined differences in hamstring muscle-tendon geometry (cross-sectional area/volume) and muscle typology (proportion of Type I/II fibers) between elite sprinters/jumpers and recreationally active individuals. This study aimed to compare hamstring geometry and typology between these groups and examine how these characteristics relate to sprint and strength performance. Elite sprint and jump athletes (n = 15, 3 female, 21.7 ± 2.2 y, 180.6 ± 9.9 cm, 72.2 ± 9.6 kg) and recreationally active individuals (n = 15, 4 female, 25.7 ± 3.0 y, 176.0 ± 9.5 cm, 76.3 ± 17.6 kg) completed sprint and eccentric knee flexor strength testing. Magnetic resonance imaging and spectroscopy were used to assess hamstring muscle-tendon geometry and typology, respectively. Compared to recreationally active individuals, elite athletes had larger hamstring muscles (all muscles, mean difference: 59.75-150.45 cm3, p < 0.009), biceps femoris long head (BFlh) proximal aponeuroses (1.09 cm3, p < 0.001), BF short head distal aponeuroses (1.24 cm3, p = 0.002), semimembranosus proximal free tendons (0.75 cm3, p = 0.024) and aponeuroses (2.29 cm3, p < 0.001), semitendinosus distal free tendons (0.49 cm3, p = 0.01) and BFlh proximal aponeurosis interface areas (10.43 cm2, p < 0.001). Elite athletes also had 1.5 times greater estimated proportion of Type II fibers (p < 0.001). Medial hamstring geometry and muscle typology explained the greatest variance in maximal sprint speed (R2 = 0.65), while BFlh and semimembranosus muscle volumes with semitendinosus tendon volume explained the greatest variance in eccentric knee flexor strength (R2 = 0.59). Elite athletes had larger hamstring muscles, aponeuroses, and free tendons, and a greater estimated proportion of Type II fibers than recreationally active individuals. These structural and compositional differences likely contribute to their superior sprint and strength performance.