Maturity-Related Differences in Muscle Architecture in Growing Female Volleyball Athletes: A Cross-Sectional Study

Background/Objectives: This cross-sectional study examined gastrocnemius medialis (GM) and vastus lateralis (VL) muscle architecture in pre-, circa- and post-peak height velocity (PHV) female volleyball athletes. Methods: Muscle architecture (fascicle length: FL; pennation angle: PA; muscle thickness: TH) was assessed in 144 athletes using ultrasonography. Stature, body mass, femur and calf length were measured. Maturity index was calculated from anthropometrics. Athletes were classified as pre-PHV, circa-PHV and post-PHV. Results: Fascicle length of the GM and VL was longer in post-PHV compared to pre-PHV athletes (d = 1.50 and d = 2.22, respectively, p < 0.001). Differences between circa and post-PHV athletes were observed only in GM (d = 0.84, p = 0.005). TH showed progressively greater values in both muscles across maturity stages (p < 0.001). PA was larger in post- compared to pre-PHV athletes, only in GM (p = 0.009). When all athletes were examined as one group, correlations were found between anthropometrics, maturity index and muscle architecture (r = 0.164-0.744 and 0.284-0.622, respectively, p < 0.05). In addition, in the GM, body mass and training experience accounted for 40% of the variance in FL (p < 0.001), whereas body mass and FL explained 66% of the variance in TH (p < 0.001). In the VL, stature and body mass explained 49% of the variance in FL (p < 0.001), while body mass, fascicle length, and maturity index explained 68% of the variance in TH, with maturity exhibiting a negative coefficient (p < 0.001). Conclusions: FL and TH of both muscles demonstrated larger values between pre- and post-PHV. GM and VL exhibited different morphological patterns, probably due to bone development and loading. Athletes' body mass best predicted FL in both muscles, whereas the greater values in TH in post- compared to pre-PHV athletes appear to be associated with body mass and FL. The influence of maturity on VL thickness diminishes at more advanced stages of development.