Physical Therapy and Rehabilitation Science, The University of Iowa, 1-252 Medical Education Bldg., Iowa City, IA 52242-1190, USA.
Clin Neurophysiol. 2012 Feb;123(2):335-43. doi: 10.1016/j.clinph.2011.06.031. Epub 2011 Jul 29.
The aim of this study was to examine the cortical and segmental excitability changes during fatigue of the soleus muscle.
Ten healthy young subjects performed 45 plantar flexion maximal voluntary contractions (MVCs) (7-s on/3-s off) in 9 epochs of five contractions. Motor evoked potentials (MEPs) using transcranial magnetic stimulation and H-reflexes were assessed during the task.
The torque and the soleus EMG activity both showed the greatest decline during the 1st epoch, followed by a gradual, but significant decrease by the end of the task (∼70% pre-fatigue). The H-reflex sampled at rest after each epoch decreased to 66.6±18.3% pre-fatigue after the first epoch, and then showed no further change. The MEP on 10% pre-fatigue MVC after each epoch increased progressively (252.9±124.2% pre-fatigue). There was no change in the MEPs on the 3rd MVC in each epoch. The silent period on the MVC increased (109.0±9.2% pre-fatigue) early with no further changes during the task.
These findings support that the motor cortex increases excitability during fatigue, but with a concomitant inhibition.
These findings are in contrast to upper extremity muscles and may reflect a distinct response specific to postural, fatigue-resistant muscle.
本研究旨在探讨跟腱肌疲劳过程中的皮质和节段兴奋性变化。
10 名健康年轻受试者进行了 45 次足底屈肌最大自主收缩（MVC）（7 秒 ON/3 秒 OFF），共 9 个 5 次收缩的时期。在任务期间评估了经颅磁刺激和 H 反射引起的运动诱发电位（MEP）。
在第 1 个时期，扭矩和比目鱼肌 EMG 活动均显示出最大的下降，随后逐渐但显著下降（约 70%疲劳前）。每个时期后在休息时采样的 H 反射降低至第 1 个时期后 66.6±18.3%疲劳前，然后没有进一步变化。每个时期的 10%MVC 后 MEP 逐渐增加（252.9±124.2%疲劳前）。每个时期的第 3 次 MVC 的 MEP 没有变化。MVC 上的静息期（109.0±9.2%疲劳前）早期增加，随后在任务中没有进一步变化。
这些发现支持运动皮层在疲劳过程中增加兴奋性，但同时存在抑制。
这些发现与上肢肌肉相反，可能反映了特定于姿势、耐疲劳肌肉的独特反应。
