Relationship between resting elasticity of quadriceps at multiple knee flexion angles and explosive athletic performance

We investigated the relationship between resting quadriceps elasticity at multiple knee flexion angles and explosive athletic performance. Thirty healthy men who exercised 4.8 ± 1.3 days/week for over a year participated. Resting muscle elasticity was assessed via shear modulus measurements of the rectus femoris (RF), vastus medialis, vastus lateralis (VL), and vastus intermedius at 0°, 30°, 60°, 90°, and 120° of knee flexion. Explosive performance was evaluated through rate of torque development (RTD), specifically RTD over the 50 ms interval (RTD50) and 100 ms interval (RTD100) from torque exertion onset. Other measures included countermovement jump (CMJ) height, and CMJ yielding and braking rates of force development (RFD). VL elasticity at 60° (r = 0.408, p = 0.025) and 120° (r = 0.420, p = 0.021) showed moderate positive correlations with RTD50. Similarly, VL elasticity at 60° (r = 0.432, p = 0.017), 90° (r = 0.370, p = 0.044), and 120° (r = 0.422, p = 0.020) showed moderate correlations with RTD100. Significant negative correlations were observed between CMJ height and RF elasticity at 120° (r = -0.407, p = 0.026) and VL elasticity at 90° (r = -0.368, p = 0.046). VL elasticity positively correlated with yielding RFD at 30° to 120° (r = 0.381-0.455, p ≤ 0.026) and with braking RFD at 0°, 30°, and 60° (r = 0.418-0.485, p ≤ 0.038). Overall, resting quadriceps elasticity-especially in the VL-was linked to components of RTD and RFD. Our results suggested that the resting elasticity of the quadriceps femoris, particularly of the VL, may influence RTD and the different stages of yielding and braking RFD that constitute CMJ performance. Thus, non-invasive muscle elasticity measurement at specific angles holds potential as a useful tool for evaluating explosive athletic performance.