(19) THIGH MUSCLE REGIONAL SIZE: RELATIONSHIPS WITH COUNTERMOVEMENT JUMP PERFORMANCE

Purpose: Associations between regional muscle size in the thigh and countermovement jump (CMJ) performance were investigated. Methods: Resistance-trained males (n=7) and females (n=4) participated in this study (age=23±2.5yrs, body mass=81.9±15.9kg, height=175.9±9.3cm, training age=7.8±3.3). In one testing session, subjects completed hydration testing prior to the collection of ultrasound images of the right vastus lateralis (VL) and rectus femoris (RF) at 33%, 50%, and 66% femur length (Logiq E9, General Electric). Following ultrasound imaging, subjects completed a standardized warm-up and CMJ testing on dual force plates sampling at 1,000 hz (ForceDecks, VALD, Newstead, Queensland). Subjects used no arm swing and were instructed to jump as high as possible during CMJ testing. CMJ testing continued until two trials were within ±2cm of jump height calculated from flight time (JH-FT). Proprietary software (ForceDecks) quantified JH-FT, concentric peak velocity (ConPV), force at zero velocity (Force-0V), and reactive strength-index modified (RSIm), averaged across two trials. Shapiro-Wilk testing indicated RSIm was not normally distributed (p< 0.05), therefore, non-parametric testing was conducted for this metric. Pearson product-moment (r) or Spearman’s rank correlations (rho) were used to evaluate relationships between regional muscle size (VL33, VL50, VL66 or RF33, RF50, RF66) and CMJ performance (JH-FT, ConPV, Force-0V, RSIm). Correlation coefficient magnitudes were interpreted as: trivial< 0.10, small=0.10–0.29, moderate=0.30–0.49, strong=0.50–0.69, very strong=0.70–0.89, or nearly perfect≥0.90 (1). Statistical analysis was conducted using JASP (ver. 0.19.3, JASP team). Results: Figure 1 depicts relationships observed between regional VL size and CMJ performance. Statistically significant relationships were observed between RF33 and RSIm (rho=0.776, p=0.005) and between RF50 and JH-FT (r=0.803, p=0.003), ConPV (r=0.726, p=0.011), and RSIm (rho=0.845, p=0.001). Relationships between RF66 and CMJ performance metrics were not statistically significant (p>0.05). Conclusions: These results show that muscle mass closer to the hip may be beneficial to CMJ performance, perhaps due to greater contributions of work at the hip (4) and reduced thigh moment of inertia (2). Importantly, regional muscle size may be more associated with movement velocity rather than muscular force during the CMJ. Practical Applications: The relationships observed support prior evidence that regional muscle size, reflecting regional mass, may influence limb mechanics and athletic performance (2,3). Considering these observations, it is recommended for sports scientists to monitor muscle size at multiple regions, particularly the proximal region, due to the strong associations with CMJ performance. Acknowledgements: None