Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan.
School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK.
Eur J Neurosci. 2021 May;53(10):3416-3432. doi: 10.1111/ejn.15197. Epub 2021 Apr 7.
It is poorly understood how the central nervous system adapts to resistance training, especially after years of exposure. We compared corticospinal excitability and motor representation assessed with transcranial magnetic stimulation (TMS) between long-term resistance trained (LRT, ≥3 years) versus untrained (UNT) males (n = 15/group). Motor-evoked potentials (MEPs) were obtained from the biceps brachii during isometric elbow flexion. Stimulus-response curves were created at the hotspot during 10% maximum voluntary torque (MVT) contractions. Maximum peak-to-peak MEP amplitude (MEPmax) was acquired with 100% stimulator output intensity, whilst 25%-100% MVT was produced. Maps were created during 10% MVT contractions, with an individualised TMS intensity eliciting 20% MEPmax at the hotspot. LRT had a 48% lower stimulus-response curve slope than UNT (p < .05). LRT also had a 66% larger absolute map size, although TMS intensity used for mapping was greater in LRT versus UNT (48% vs. 26% above active motor threshold) to achieve a target 20% MEPmax at the hotspot, due to the lower slope of LRT. Map size was strongly correlated with the TMS intensity used for mapping (r = 0.776, p < .001). Once map size was normalised to TMS intensity, there was no difference between the groups (p = .683). We conclude that LRT had a lower stimulus-response curve slope/excitability, suggesting higher neural efficiency. TMS map size was overwhelmingly determined by TMS intensity, even when the MEP response at the hotspot was matched among individuals, likely due to larger current spread with higher intensities. Motor representation appears similar between LRT and UNT given no difference in the normalised map size.
人体中枢神经系统如何适应抗阻训练，尤其是在多年暴露之后，目前人们对此知之甚少。我们对比了长期抗阻训练者（LRT，≥3 年）和未训练者（UNT）男性（每组 15 人）的皮质脊髓兴奋性和经颅磁刺激（TMS）评估的运动代表[1]。在等长肘屈时，从肱二头肌获得运动诱发电位（MEP）。在 10%最大自主扭矩（MVT）收缩时，在热点处创建刺激-反应曲线[1]。使用 100%刺激器输出强度获得最大峰峰值 MEP 幅度（MEPmax），而产生 25%-100% MVT[1]。在 10%MVT 收缩期间创建图谱，使用个体化 TMS 强度在热点处引发 20%MEPmax[1]。与 UNT 相比，LRT 的刺激-反应曲线斜率低 48%（p<.05）[1]。LRT 的绝对图谱大小也大 66%，尽管为了在热点处达到目标 20%MEPmax，LRT 中用于映射的 TMS 强度比 UNT 更大（高于主动运动阈值的 48%比 26%），因为 LRT 的斜率较低[1]。图谱大小与用于映射的 TMS 强度呈强相关（r=0.776，p<.001）[1]。一旦将图谱大小归一化到 TMS 强度，两组之间就没有差异（p=0.683）[1]。我们得出结论，LRT 的刺激-反应曲线斜率/兴奋性较低，提示神经效率更高[1]。TMS 图谱大小主要由 TMS 强度决定，即使在个体之间热点处的 MEP 反应相匹配时也是如此，这可能是由于更高的强度会导致更大的电流扩散[1]。考虑到正常化后的图谱大小没有差异，LRT 和 UNT 之间的运动代表似乎相似[1]。
