Doguet Valentin, Nosaka Kazunori, Guével Arnaud, Thickbroom Gary, Ishimura Kazuhiro, Jubeau Marc
Laboratory 'Movement, Interactions, Performance', EA 4334, Faculty of Sport Sciences, University of Nantes, Nantes, France.
Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia.
Exp Physiol. 2017 Nov 1;102(11):1513-1523. doi: 10.1113/EP086480. Epub 2017 Sep 30.
What is the central question of this study? Does sensory input from peripheral mechanoreceptors determine the specific neural control of eccentric contractions? How corticospinal excitability (i.e. muscle responses to motor cortex stimulation) is affected by muscle length has never been investigated during eccentric contractions. What is the main finding and its importance? Muscle length does not influence corticospinal excitability during concentric and isometric maximal contractions, but does during eccentric maximal contractions. This indicates that neural control in eccentric contractions differs from that in concentric and isometric contractions. Neural control of eccentric contractions differs from that of concentric and isometric contractions, but no previous study has compared responses to motor cortex stimulations at long muscle lengths during such contraction types. In this study, we compared the effect of muscle length on corticospinal excitability between maximal concentric, isometric and eccentric contractions of the knee extensors. Twelve men performed 12 maximal concentric, isometric and eccentric voluntary contractions (36 contractions in total), separated by a 5 min rest between contraction types. The 12 contractions for the same contraction type were performed every 10 s, and transcranial magnetic stimulations (first eight contractions) and electrical femoral nerve stimulations (last four contractions) were superimposed alternately at 75 and 100 deg of knee flexion. Average motor evoked potential amplitude, normalized to the maximal M wave amplitude (MEP/M) and cortical silent period duration were calculated for each angle and compared among the contraction types. The MEP/M was lower (-23 and -28%, respectively) during eccentric than both concentric and isometric contractions at 75 deg, but similar between contraction types at 100 deg (P < 0.05). The cortical silent period duration was shorter (-12 and -10%, respectively) during eccentric than both concentric and isometric contractions at 75 deg, but longer (+11 and +9%, respectively) during eccentric contractions at 100 deg (P < 0.05). These results show that corticospinal excitability during eccentric contractions is angle dependent such that cortical inhibitory processes are greater with no alteration of corticospinal excitability at 100 deg, whereas this control is reversed at 75 deg.
本研究的核心问题是什么？来自外周机械感受器的感觉输入是否决定了离心收缩的特定神经控制？在离心收缩过程中，肌肉长度如何影响皮质脊髓兴奋性（即肌肉对运动皮层刺激的反应）从未得到过研究。主要发现及其重要性是什么？在向心和等长最大收缩过程中，肌肉长度不影响皮质脊髓兴奋性，但在离心最大收缩过程中会有影响。这表明离心收缩中的神经控制与向心和等长收缩中的不同。离心收缩的神经控制与向心和等长收缩不同，但此前没有研究比较过在这种收缩类型下长肌肉长度时对运动皮层刺激的反应。在本研究中，我们比较了膝关节伸肌最大向心、等长和离心收缩时肌肉长度对皮质脊髓兴奋性的影响。12名男性进行了12次最大向心、等长和离心自主收缩（共36次收缩），不同收缩类型之间间隔5分钟休息。相同收缩类型的12次收缩每隔10秒进行一次，在膝关节屈曲75度和100度时交替叠加经颅磁刺激（前八次收缩）和股神经电刺激（最后四次收缩）。计算每个角度的平均运动诱发电位幅度（以最大M波幅度归一化，即MEP/M）和皮质静息期持续时间，并在不同收缩类型之间进行比较。在75度时，离心收缩时的MEP/M低于向心和等长收缩（分别低23%和28%），但在100度时不同收缩类型之间相似（P<0.05）。在75度时，离心收缩时的皮质静息期持续时间短于向心和等长收缩（分别短12%和10%），但在100度时离心收缩时更长（分别长11%和9%）（P<0.05）。这些结果表明，离心收缩过程中的皮质脊髓兴奋性与角度有关，即在100度时皮质抑制过程更强，而皮质脊髓兴奋性无变化，而在75度时这种控制情况相反。
