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° knee angle and calculated in different 50-ms epochs (0-50, 50-100, 100-150, 150-200 and 200-250ms). The maximum voluntary contraction was also recorded.

Results: Large correlations were observed between vastus intermedius muscle thickness and the 100-150ms (r=0.694, p=0.004), 150-200ms (r=0.597, p=0.019) and 200-250ms (r=0.546, p=0.045) epochs. Large correlation was observed between vastus intermedius normalized fascicle length and 100-150ms (r=0.570, p=0.043) and large correlations with 150-200ms (r=0.643, p=0.010) and 200-250ms (r=0.629, p=0.012) epochs. Additionally, large correlations were observed between vastus lateralis normalized fascicle length and the 100-150ms (r=0.535, p=0.049), 150-200ms (r=0.629, p=0.016) and 200-250ms (r=0.563, p=0.046) epochs. Vastus intermedius muscle thickness predicted 59% (R2=0.581, p=0.002) of the RFD of the 100-150ms epoch; vastus intermedius muscle thickness and fascicle length predicted 51% (R2=0.506, p=0.029) of the 150-200ms epoch; vastus intermedius and vastus lateralis fascicle length predicted 48% (R2=0.483, p=0.037) of the 200-250ms 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.

研究目的：本研究旨在探讨股四头肌肌肉结构与膝伸展肌力发展速率（Rate of Force Development, RFD）之间的相关性。

研究设计：横断面研究。

研究方法：通过超声测量股外侧肌、股直肌、股中间肌及股内侧肌的肌肉厚度、羽状角及按大腿长度归一化的肌束长度。在膝关节角度为90°的状态下进行等长收缩评估膝伸展肌力发展速率，并在不同50毫秒时段（0-50、50-100、100-150、150-200及200-250ms）进行计算。同时记录最大自主收缩力量。

研究结果：股中间肌肌肉厚度与100-150ms时段（r=0.694, p=0.004）、150-200ms时段（r=0.597, p=0.019）及200-250ms时段（r=0.546, p=0.045）呈强相关性。股中间肌归一化肌束长度与100-150ms时段（r=0.570, p=0.043）呈强相关，与150-200ms时段（r=0.643, p=0.010）及200-250ms时段（r=0.629, p=0.012）呈强相关性。此外，股外侧肌归一化肌束长度与100-150ms时段（r=0.535, p=0.049）、150-200ms时段（r=0.629, p=0.016）及200-250ms时段（r=0.563, p=0.046）呈强相关性。股中间肌肌肉厚度可解释100-150ms时段肌力发展速率变异的59%（R²=0.581, p=0.002）；股中间肌肌肉厚度及肌束长度可解释150-200ms时段变异的51%（R²=0.506, p=0.029）；股中间肌与股外侧肌的肌束长度可解释200-250ms时段变异的48%（R²=0.483, p=0.037）。未观察到其余显著相关性。

研究结论：肌束长度与肌肉厚度可预测肌力发展速率的晚期阶段。股中间肌的肌肉结构在膝伸展肌力发展速率中发挥主要作用。