Vastus intermedius muscle architecture predicts the late phase of the knee extension rate of force development in recreationally resistance-trained men

Objectives: The current study investigated the correlation between quadriceps muscle architecture and the knee extension rate of force development (RFD). Design: cross-sectional study. Methods: Muscle thickness, pennation angle and fascicle length normalized per the thigh-length were measured via ultrasound in vastus lateralis, rectus femoris, vastus intermedius and vastus medialis. The knee extension rate of force was assessed isometrically at 90 degrees knee angle and calculated in different 50-ms epochs (0-50, 50-100, 100-150, 150-200 and 200-250 ms). The maximum voluntary contraction was also recorded. Results: Large correlations were observed between vastus intermedius muscle thickness and the 100-150 ms (r = 0.694, p = 0.004), 150-200 ms (r = 0.597, p = 0.019) and 200-250 ms (r = 0.546, p = 0.045) epochs. Large correlation was observed between vastus intermedius normalized fascicle length and 100-150 ms (r = 0.570, p = 0.043) and large correlations with 150-200 ms (r = 0.643, p = 0.010) and 200-250 ms (r = 0.629, p = 0.012) epochs. Additionally, large correlations were observed between vastus lateralis normalized fascicle length and the 100-150 ms (r = 0.535, p = 0.049), 150-200 ms (r = 0.629, p = 0.016) and 200-250 ms (r = 0.563, p = 0.046) epochs. Vastus intermedius muscle thickness predicted 59% (R-2 = 0.581, p = 0.002) of the RFD of the 100-150 ms epoch; vastus intermedius muscle thickness and fascicle length predicted 51% (R-2 = 0.506, p = 0.029) of the 150-200 ms epoch; vastus intermedius and vastus lateralis fascicle length predicted 48% (R-2 = 0.483, p = 0.037) of the 200-250 ms epoch. No further correlation was observed. Conclusions: Fascicle length and muscle thickness were observed as predictive of the late phase of the rate of force development. Vastus intermedius muscle architecture has a primary role in the knee extension RFD. (C) 2020 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.