Data from studies of elbow-flexor (EF) or knee-extensor (KE) muscles suggest that a fatigue-related decrease in motoneuron excitability only occurs in EF. It is unknown how motoneuron excitability changes after sustained fatiguing maximal voluntary isometric contractions (MVICs) in EF and KE in the same participants. In two sessions, eight healthy men performed a 2-min MVIC of EF or KE to induce fatigue with brief MVICs before and six times after the 2-min MVIC. Electromyographic responses elicited by corticospinal tract stimulation at the transmastoid [cervicomedullary motor-evoked potential (CMEP)] or thoracic [thoracic motor-evoked potential (TMEP)] level were recorded from EF and KE, respectively. To account for muscle excitability, CMEPs and TMEPs were normalized to maximal M-wave (M_max) elicited by peripheral nerve stimulation during each brief MVIC. Immediately after the 2-min MVIC, biceps brachii and brachioradialis CMEP/M_max were 88% (SD 11%) (P = 0.026) and 87% (SD 12%) (P = 0.029) of pre-MVIC values, respectively, and remained lower than PRE after 5 s of recovery [91% (SD 8%), P = 0.036 and 87% (SD 13%), P = 0.046, respectively]. No subsequent time points differed from PRE (all P ³ 0.253). TMEP/M_max for rectus femoris and vastus lateralis were not different from PRE at any time during the recovery period (all P > 0.050). A different recovery pattern in motoneuron excitability occurred in EF as it recovered by 60 s whereas KE motoneurons were unaffected by the fatiguing task. The present findings may contribute to better understand muscle-specific neurophysiological differences in spinal excitability.

中文翻译：

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在最大持续疲劳任务后，肘屈肌和膝伸肌对神经肌肉恢复的脊柱贡献不同。

来自肘屈肌 (EF) 或膝伸肌 (KE) 肌肉研究的数据表明，运动神经元兴奋性与疲劳相关的降低仅发生在 EF。目前尚不清楚同一参与者在 EF 和 KE 中持续疲劳的最大自愿等长收缩 (MVIC) 后运动神经元兴奋性如何变化。在两次会议中，八名健康男性在 2 分钟 MVIC 之前和之后 6 次进行了 2 分钟的 EF 或 KE MVIC，以诱导疲劳。分别从 EF 和 KE 记录由皮质脊髓束刺激在经乳突 [颈髓运动诱发电位 (CMEP)] 或胸[胸运动诱发电位 (TMEP)] 水平引起的肌电图反应。为了解释肌肉兴奋性，CMEPs 和 TMEPs 被标准化为最大 M 波（M _max) 在每个简短的 MVIC 期间由外周神经刺激引起。2 分钟 MVIC 后，肱二头肌和肱桡肌 CMEP/M_最大值分别为MVIC 前_值的 88% (SD 11%) (P = 0.026) 和 87% (SD 12%) (P = 0.029)，并且在恢复 5 秒后仍低于 PRE [91% (SD 8%)，分别为 P = 0.036 和 87% (SD 13%)，P = 0.046]。没有后续时间点与 PRE 不同（所有 P ³ 0.253）。TMEP/M_最大值股直肌和股外侧肌在恢复期的任何时间均与 PRE 无差异（均 P > 0.050）。运动神经元兴奋性的不同恢复模式发生在 EF 中，因为它在 60 秒后恢复，而 KE 运动神经元不受疲劳任务的影响。目前的研究结果可能有助于更好地了解脊髓兴奋性的肌肉特异性神经生理学差异。