Muscle enlargement in sumo wrestlers includes increased muscle fascicle length.

Abstract

Skeletal muscle architecture was measured in 28 college sumo wrestlers (Sumo) and 30 control subjects. Pennation angle (PAN) and muscle thickness (MTH) of the triceps long head (TL), vastus lateralis (VL) and gastrocnemius medialis (MG) and lateralis (LG) muscles were measured by B-mode ultrasonography, and fascicle length (FAL) was estimated. Sumo wrestlers had a significantly greater percentage body fat [mean (SD) 33.9 (9.4)%], fat mass [41.7 (18.5) kg], and fat-free mass [76.8 (7.5) kg] than the controls [15.6 (2.5)%, 9.3 (2.4) kg, and 49.9 (6.2) kg, respectively]. MTH was between 18 and 35% greater in sumo wrestlers than in controls. The sumo wrestlers had a significantly greater PAN in the TL, MG and LG muscles than did the controls, but not in the VL. There were significant correlations between PAN and MTH for the sumo wrestlers (r values from 0.33 to 0.57), suggesting that PAN is a function of the relative state of muscle enlargement. FAL was greater (P < 0.01) in the Sumo group for TL (7.26 cm vs 6.13 cm), VL (10.01 cm vs 6.97 cm) and MG (6.41 cm vs 5.53 cm) than in the controls, but not for LG (7.61 cm vs 7.04 cm). Relative FAL correlated significantly with MTH for these muscles in the Sumo group [r values from 0.45 (P < 0.05) to 0.71 (P < 0.01)]. There appear to be architectural differences in the muscle fascicles between sumo wrestlers and controls, with sumo wrestlers having longer fascicles. A greater FAL appears to limit the degree of change in PAN associated with the extreme muscle enlargement seen in sumo wrestlers. This architectural alteration may ultimately improve the expression of the force/cross-sectional area relationship with extreme muscle enlargement.