Sharples Simon A, Gould Jason A, Vandenberk Michael S, Kalmar Jayne M
Department of Kinesiology, Wilfrid Laurier University, Waterloo, ON, Canada.
PLoS One. 2016 Feb 9;11(2):e0149026. doi: 10.1371/journal.pone.0149026. eCollection 2016.
The purpose of this study was to investigate cortical mechanisms upstream to the corticospinal motor neuron that may be associated with central fatigue and sense of effort during and after a fatigue task. We used two different isometric finger abduction protocols to examine the effects of muscle activation and fatigue the right first dorsal interosseous (FDI) of 12 participants. One protocol was intended to assess the effects of muscle activation with minimal fatigue (control) and the other was intended to elicit central fatigue (fatigue). We hypothesized that high frequency repetitive transcranial magnetic stimulation (rTMS) of the supplementary motor area (SMA) would hasten recovery from central fatigue and offset a fatigue-induced increase in sense of effort by facilitating the primary motor cortex (M1). Constant force-sensation contractions were used to assess sense of effort associated with muscle contraction. Paired-pulse TMS was used to assess intracortical inhibition (ICI) and facilitation (ICF) in the active M1 and interhemispheric inhibitory (IHI) was assessed to determine if compensation occurs via the resting M1. These measures were made during and after the muscle contraction protocols. Corticospinal excitability progressively declined with fatigue in the active hemisphere. ICF increased at task failure and ICI was also reduced at task failure with no changes in IHI found. Although fatigue is associated with progressive reductions in corticospinal excitability, compensatory changes in inhibition and facilitation may act within, but not between hemispheres of the M1. rTMS of the SMA following fatigue enhanced recovery of maximal voluntary force and higher levels of ICF were associated with lower sense of effort following stimulation. rTMS of the SMA may have reduced the amount of upstream drive required to maintain motor output, thus contributing to a lower sense of effort and increased rate of recovery of maximal force.
本研究的目的是探究皮质脊髓运动神经元上游的皮质机制,这些机制可能与疲劳任务期间及之后的中枢性疲劳和用力感觉有关。我们采用两种不同的等长手指外展方案,来检测12名参与者右侧第一背侧骨间肌(FDI)的肌肉激活和疲劳效应。一种方案旨在评估最小疲劳状态下肌肉激活的效应(对照组),另一种方案旨在引发中枢性疲劳(疲劳组)。我们假设,对辅助运动区(SMA)进行高频重复经颅磁刺激(rTMS)将加速从中枢性疲劳中恢复,并通过促进初级运动皮层(M1)来抵消疲劳引起的用力感觉增加。采用恒力感觉收缩来评估与肌肉收缩相关的用力感觉。使用配对脉冲TMS评估活跃M1中的皮质内抑制(ICI)和易化(ICF),并评估半球间抑制(IHI)以确定是否通过静息M1发生代偿。这些测量在肌肉收缩方案期间及之后进行。在活跃半球中,皮质脊髓兴奋性随疲劳逐渐下降。在任务失败时ICF增加,ICI在任务失败时也降低,未发现IHI有变化。尽管疲劳与皮质脊髓兴奋性的逐渐降低有关,但抑制和易化的代偿性变化可能在M1的半球内起作用,而非在半球间起作用。疲劳后对SMA进行rTMS可增强最大自主力量的恢复,刺激后较高水平的ICF与较低的用力感觉相关。对SMA进行rTMS可能减少了维持运动输出所需的上游驱动量,从而导致较低的用力感觉和最大力量恢复速率增加。