Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy.
Department of Clinical and Experimental Medicine, University of Catanzaro "Magna Græcia", Catanzaro, Italy.
J Neurophysiol. 2023 Jun 1;129(6):1310-1321. doi: 10.1152/jn.00085.2023. Epub 2023 May 10.
Superimposing neuromuscular electrical stimulation (NMES) on voluntary muscle contractions has shown the potential to improve motor performance even more than voluntary exercise alone. Nevertheless, the neurophysiological and neurocognitive mechanisms underlying this technique are still unclear. The aim of this study was to investigate the acute responses in spinal excitability and brain activity following three conditions: NMES superimposed on isometric contractions (NMES + ISO), passive NMES, and voluntary isometric contractions (ISO). Each condition involved 15 intermittent ankle plantar-flexions at submaximal level. Before and after each condition, tibial nerve stimulation was used to elicit H-reflexes, which represent a measure of spinal excitability, and somatosensory evoked potentials (SEPs), which index the activity of subcortical and cortical somatosensory areas. H-reflex amplitudes increased after NMES + ISO and decreased after passive NMES compared with baseline values, whereas they remained unaltered after ISO. Subcortical lemniscal activity remained unaltered after the three conditions. Activity in both primary and secondary somatosensory cortices (S1 and S2) increased after NMES + ISO and decreased after the ISO condition, whereas no differences emerged after NMES. At later stages of S2 processing, ISO induced no changes in cortical activity, which, conversely, increased after NMES and NMES + ISO. These findings indicate that the beneficial effects of NMES may be mediated by potentiation of the reflex pathways at the spinal level. At the brain level, peripheral input representation in the brain stem was not influenced by the experimental conditions, which, conversely, altered cortical activity by affecting synaptic efficiency through the somatosensory pathway. Neuromuscular electrical stimulation superimposed on voluntary contractions (NMES+) is effective to improve motor performance in several populations. Here, we investigated the changes in cortical activation and reflex response following three acute conditions, including NMES+. Our results show that NMES+ has a greater excitatory effect at both spinal and cortical levels compared with passive stimulation and voluntary exercise alone. These results open up original perspectives for the implementation of NMES+ in neurorehabilitation and training environments.
叠加神经肌肉电刺激 (NMES) 于自主肌肉收缩，相较于单纯自主运动，已显示出改善运动表现的潜力。然而，这种技术背后的神经生理和神经认知机制仍不清楚。本研究旨在探讨三种条件下脊髓兴奋性和大脑活动的急性反应：叠加等长收缩的 NMES (NMES + ISO)、被动 NMES 和自主等长收缩 (ISO)。每种情况都涉及 15 次亚最大水平的间歇性踝关节跖屈。在每种情况之前和之后，使用胫神经刺激来引出 H 反射，它代表了脊髓兴奋性的一个测量值，以及体感诱发电位 (SEPs)，它指标了皮质下和皮质体感区域的活动。与基线值相比，NMES + ISO 后 H 反射幅度增加，而被动 NMES 后减少，而 ISO 后则保持不变。三种情况下，皮质下的丘系活动保持不变。NMES + ISO 后，初级和次级体感皮层 (S1 和 S2) 的活动增加，而 ISO 后则减少，而 NMES 后则没有差异。在 S2 处理的后期阶段，ISO 没有引起皮质活动的变化，而 NMES 和 NMES + ISO 后则增加了皮质活动。这些发现表明，NMES 的有益效果可能是通过在脊髓水平增强反射途径来介导的。在大脑水平，脑干中的外周输入表示不受实验条件的影响，而相反，通过体感途径影响突触效率，改变了皮质活动。叠加于自主收缩的神经肌肉电刺激 (NMES+) 在多个人群中有效改善运动表现。在这里，我们研究了三种急性条件下皮质激活和反射反应的变化，包括 NMES+。我们的结果表明，与被动刺激和单纯自主运动相比，NMES+ 在脊髓和皮质水平都具有更大的兴奋作用。这些结果为 NMES+在神经康复和训练环境中的实施开辟了新的视角。
