Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Australia.
Department of Physical Therapy, College of Staten Island, The City University of New York, Staten Island, New York.
J Neurophysiol. 2020 May 1;123(5):1896-1906. doi: 10.1152/jn.00578.2019. Epub 2020 Apr 8.
This study investigated whether modulation of corticospinal-motoneuronal excitability and/or synaptic transmission of the Ia afferent spinal reflex contributes to decreases in voluntary activation and muscular force after an acute bout of prolonged static muscle stretching. Fifteen men performed five 60-s constant-torque stretches (15-s rest intervals; total duration 5 min) of the plantar flexors on an isokinetic dynamometer and a nonstretching control condition in random order on 2 separate days. Maximum isometric plantar flexor torque and triceps surae muscle electromyographic activity (normalized to M wave; EMG/M) were simultaneously recorded immediately before and after each condition. Motor-evoked potentials (using transcranial magnetic stimulation) and H-reflexes were recorded from soleus during EMG-controlled submaximal contractions (23.4 ± 6.9% EMG maximum). No changes were detected in the control condition. After stretching, however, peak torque (mean ± SD; -14.3 ± 7.0%) and soleus EMG/M (-17.8 ± 6.2%) decreased, and these changes were highly correlated ( = 0.83). No changes were observed after stretching in soleus MEP or H-reflex amplitudes measured during submaximal contractions, and interindividual variability of changes was not correlated with changes in EMG activity or maximum torque. During EMG-controlled submaximal contractions, torque production was significantly decreased after stretching (-22.7 ± 15.0%), indicating a compromised muscular output. These data provide support that changes in the excitability of the corticospinal-motoneuronal and Ia afferent spinal reflex pathways do not contribute to poststretch neural impairment. This study is the first to specifically examine potential sites underlying the decreases in neural activation of muscle and force production after a bout of muscle stretching. However, no changes were found in either the H-reflex or motor-evoked potential amplitude during submaximal contractions.
本研究旨在探讨急性长时间静态肌肉拉伸后，皮质脊髓运动神经元兴奋性和/或 Ia 传入脊髓反射的突触传递的调节是否有助于降低自愿激活和肌肉力量。15 名男性在等速测力计上进行 5 次持续 60 秒的足底屈肌等长伸展（15 秒休息间隔；总持续时间 5 分钟），并在 2 天内随机顺序进行非伸展对照条件。在每种情况下之前和之后，立即同时记录最大等长足底屈肌扭矩和比目鱼肌肌电图活动（归一化为 M 波；EMG/M）。在肌电图控制的次最大收缩期间（23.4 ± 6.9% EMG 最大值），从比目鱼肌记录运动诱发电位（使用经颅磁刺激）和 H 反射。在对照条件下未检测到变化。然而，拉伸后，峰值扭矩（平均值 ± SD；-14.3 ± 7.0%）和比目鱼肌 EMG/M（-17.8 ± 6.2%）下降，这些变化高度相关（r = 0.83）。在次最大收缩期间测量的比目鱼肌 MEP 或 H 反射幅度在拉伸后没有观察到变化，个体间变化的可变性与 EMG 活动或最大扭矩的变化无关。在肌电图控制的次最大收缩期间，扭矩产生在拉伸后显著降低（-22.7 ± 15.0%），表明肌肉输出受损。这些数据支持皮质脊髓运动神经元和 Ia 传入脊髓反射途径的兴奋性变化不会导致拉伸后神经损伤的观点。本研究首次专门研究肌肉拉伸后肌肉神经激活和力量产生减少的潜在部位。然而，在次最大收缩期间，无论是 H 反射还是运动诱发电位幅度都没有发现变化。
