Objective: We examined vastus lateralis (VL), gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and biceps femoris (BF) muscle architecture and force–time parameters recorded during a countermovement jump (CMJ). Methods: Eighty-nine 9 year-old girls (43 rhythmic gymnasts and 46 recreationally active controls) were assessed in: (a) muscle architecture (fascicle length—FL; angle; muscle thickness; and anatomical cross-sectional area—CSA) using ultrasonography, (b) CMJ performance (maximum force—Fmax; rate of force development—RFD; jump height; and peak power) using force–time data, and (c) anthropometrics and body composition. Results: Rhythmic gymnasts exhibited greater BF fascicle length and muscle thickness than controls (7.84 ± 0.73 vs. 7.26 ± 0.75 cm and 1.76 ± 0.19 vs. 1.61 ± 0.22 cm, respectively, p < 0.001), while VL muscle CSA was larger in controls (p = 0.001). When normalized to the respective segment length (thigh or shank), the FL was longer in gymnasts across all muscles (p ≤ 0.017). Gymnasts also demonstrated greater CMJ height (13.1%, p = 0.005), power scaled to body mass, and RFD (p < 0.005), while controls produced a greater Fmax (16.9%, p = 0.002). Body mass was the strongest predictor of Fmax in both groups (p < 0.001). CMJ power was best predicted by gastrocnemius CSA in gymnasts and by VL CSA combined with maturity offset in controls (all p < 0.001). Maturity offset and gastrocnemius CSA also predicted allometrically scaled power in controls. Conclusions: Rhythmic gymnasts are characterized by muscle-specific adaptations, specifically in the BF muscle FL and muscle thickness, which favor superior CMJ performance. In developing athletes, body mass is primarily related to maximal force, whereas muscle CSA is more closely associated with power output.
Gaspari et al. (Sat,) studied this question.