We examined whether transcranial magnetic stimulation (TMS) delivered to the motor cortex allows assessment of muscle relaxation rates in unfatigued and fatigued knee extensors (KE). We assessed the ability of this technique to measure time course of fatigue-induced changes in muscle relaxation rate and compared relaxation rate from resting twitches evoked by femoral nerve stimulation. Twelve healthy men performed maximal voluntary isometric contractions (MVC) twice before (PRE) and once at the end of a 2-min KE MVC and five more times within 8 min during recovery. Relative (intraclass correlation coefficient; ICC_2,1) and absolute (repeatability coefficient) reliability and variability (coefficient of variation) were assessed. Time course of fatigue-induced changes in muscle relaxation rate was tested with generalized estimating equations. In unfatigued KE, peak relaxation rate coefficient of variation and repeatability coefficient were similar for both techniques. Mean (95% CI) ICC_2,1 for peak relaxation rates were 0.933 (0.724–0.982) and 0.889 (0.603–0.968) for TMS and femoral nerve stimulation, respectively. TMS-induced normalized muscle relaxation rate was − 11.5 ± 2.5 s⁻¹ at PRE, decreased to − 6.9 ± 1.2 s⁻¹ (− 37 ± 17%, P < 0.001), and recovered by 2 min post-exercise. Normalized peak relaxation rate for resting twitch did not show a fatigue-induced change. During fatiguing KE exercise, the change in muscle relaxation rate as determined by the two techniques was different. TMS provides reliable values of muscle relaxation rates. Furthermore, it is sufficiently sensitive and more appropriate than the resting twitch evoked by femoral nerve stimulation to reveal fatigue-induced changes in KE.

我们检查了传递至运动皮层的经颅磁刺激（TMS）是否可以评估未疲劳和疲劳的膝盖伸肌（KE）的肌肉松弛率。我们评估了这项技术测量疲劳引起的肌肉松弛率变化时程的能力，并比较了股神经刺激引起的静止抽搐的松弛率。12名健康男性在进行PRE前两次进行最大自愿等距收缩（MVC），在2分钟KE MVC结束时进行一次最大自愿等距收缩，在恢复期间8分钟内进行五次以上。相对（类内相关系数； ICC _2,1）和绝对（重复性系数）可靠性和变异性（变异系数）进行了评估。用广义估计方程测试了疲劳引起的肌肉松弛率变化的时程。在未疲劳的KE中，两种技术的峰弛豫速率变异系数和重复性系数相似。对于TMS和股神经刺激，峰值松弛率的平均（95％CI）ICC _2,1分别为0.933（0.724-0.982）和0.889（0.603-0.968）。TMS诱导的归一化肌肉松弛率在PRE时为− 11.5±2.5 s ^-1，下降至− 6.9±1.2 s ^-1（-37±17％，P <0.001），并在运动后2分钟恢复。静息抽搐的标准化峰值松弛率未显示疲劳引起的变化。在使KE运动疲劳的过程中，通过两种技术确定的肌肉放松速率的变化是不同的。TMS提供可靠的肌肉松弛率值。此外，它比股神经刺激引起的静息抽搐足够敏感，更适合揭示疲劳引起的KE变化。