Inter-University Laboratory of Human Movement Biology (EA 7424), UJM-Saint-Etienne, Université de Lyon, 42023, Saint-Etienne, France.
Department of Biomedical Sciences for Health, Università degli Studi di Milano, Building 2, via G. Colombo 71, 20133, Milan, Italy.
Eur J Appl Physiol. 2022 Sep;122(9):2049-2059. doi: 10.1007/s00421-022-04990-8. Epub 2022 Jul 6.
This study aimed to evaluate the acute changes in the knee extensors maximum voluntary isometric contraction force (MVIC), rate of force development (RFD), and rate of EMG rise (RER) following a bout of downhill running.
MVIC and RFD at 0-50, 50-100, 100-200, and 0-200 ms were determined in thirteen men (22 ± 2 yr) before and after 30 min of downhill running (speed: 10 km h; slope: - 20%). Vastus lateralis maximum EMG (EMG) and RER at 0-30, 0-50, and 0-75 ms were also recorded.
MVIC, RFD, and EMG decreased by ~ 25% [Cohen's d = - 1.09 (95% confidence interval: - 1.88/- 0.24)], ~ 15% [d = - 0.50 (- 1.26/0.30)], and ~ 22% [d = - 0.37 (- 1.13/0.42)] (all P < 0.05), respectively. RFD was also reduced [- 25%; d = - 0.70 (- 1.47/0.11); P < 0.001]. No change was observed at 0-50 ms and 50-100 ms (P ≥ 0.05). RER values were similar at each time interval (all P > 0.05).
Downhill running impairs the muscle capacity to produce maximum force and the overall ability to rapidly develop force. No change was observed for the early phase of the RFD and the absolute RER, suggesting no alterations in the neural mechanisms underlying RFD. RFD reduction suggests that impairments in the rapid force-generating capacity are located within the skeletal muscle, likely due to a reduction in muscle-tendon stiffness and/or impairments in the muscle contractile apparatus. These findings may help explain evidence of neuromuscular alterations in trail runners and following prolonged duration races wherein cumulative eccentric loading is high.
本研究旨在评估下坡跑后膝关节伸肌最大等长收缩力（MVIC）、力发展速率（RFD）和肌电图上升率（RER）的急性变化。
13 名男性（22±2 岁）在进行 30 分钟下坡跑（速度：10km/h；坡度：-20%）前后，分别测定 0-50、50-100、100-200 和 0-200ms 时的 MVIC 和 RFD。还记录了股外侧肌最大肌电图（EMG）和 0-30、0-50 和 0-75ms 时的 RER。
MVIC、RFD 和 EMG 分别下降了约 25%[Cohen's d=-1.09（95%置信区间：-1.88/-0.24）]、约 15%[d=-0.50（-1.26/0.30）]和约 22%[d=-0.37（-1.13/0.42）]（均 P<0.05）。RFD 也降低了[-25%；d=-0.70（-1.47/0.11）；P<0.001]。0-50ms 和 50-100ms 时没有变化（均 P≥0.05）。各时间间隔的 RER 值相似（均 P>0.05）。
下坡跑会损害肌肉产生最大力的能力和快速发力的整体能力。RFD 的早期阶段和绝对 RER 没有变化，这表明 RFD 背后的神经机制没有改变。RFD 的降低表明，快速发力能力的损伤位于骨骼肌内，可能是由于肌肉肌腱刚度降低和/或肌肉收缩装置损伤所致。这些发现可能有助于解释在越野跑运动员和长时间比赛中（累积离心负荷较高）出现的神经肌肉改变的证据。
