Borzuola R, Nuccio S, Del Vecchio A, Bazzucchi I, Felici F, De Vito G, Macaluso A
Department of Movement, Human, and Health Sciences, University of Rome "Foro Italico", Rome, Italy.
Department Artificial Intelligence in Biomedical Engineering, Faculty of Engineering, Zentralinstitut für Medizintechnik (ZIMT), Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany.
Front Physiol. 2025 Jul 18;16:1590949. doi: 10.3389/fphys.2025.1590949. eCollection 2025.
Superimposing neuromuscular electrical stimulation (NMES) onto voluntary contractions induces specific neuro-physiological adaptations that may have a direct effect on force related outcomes. This study investigated motor unit discharge characteristics and force steadiness following three acute experimental conditions: NMES superimposed onto isometric contractions (NMES + ISO), passive NMES, and isometric contractions only (ISO).
Seventeen healthy volunteers participated in the study. Each condition involved 20 intermittent (6s contraction/6s rest) isometric ankle dorsi flexions at 20% of their maximum voluntary contraction (MVIC). NMES was delivered to the tibialis anterior (TA) during NMES and NMES + ISO. High-density surface electromyography (HDsEMG) was used to record myoelectric activity in the TA during steady force-matching contractions, at 10% MVIC, performed immediately after each experimental condition. Motor unit discharge rate (DR) and inter-spike variability (ISIvar) were analyzed from decomposed HDsEMG signals. Coherence analysis was performed to evaluate the strength of common synaptic input across different frequency bands and the proportion of common synaptic input (pCSI) received by spinal motoneurons. Force steadiness was evaluated using the coefficient of variation of force (Force).
NMES + ISO significantly increased motor unit DR compared to baseline and post-intervention NMES. NMES + ISO also induced an increase in pCSI compared to baseline, ISO and NMES. Force was reduced after NMES + ISO compared to all experimental conditions, indicating improved force steadiness.
These results suggest that superimposing NMES onto voluntary contractions can enhance motor unit firing rate and pCSI at low force levels. These adaptations seem to positively contribute to force steadiness, likely by engaging filtering mechanisms which minimize the independent synaptic noise affecting motor control. These findings provide new perspectives on the adaptations induced by NMES exercise, highlighting some of the neuro-physiological mechanisms involved and enriching our knowledge of how the neuromuscular system responds and adapts to NMES-based interventions.
将神经肌肉电刺激（NMES）叠加到自主收缩上会引发特定的神经生理适应性变化，这可能会对与力量相关的结果产生直接影响。本研究调查了三种急性实验条件下的运动单位放电特征和力量稳定性：NMES叠加到等长收缩上（NMES + ISO）、被动NMES以及仅进行等长收缩（ISO）。
17名健康志愿者参与了本研究。每种条件下均进行20次间歇性（6秒收缩/6秒休息）的等长踝关节背屈，强度为其最大自主收缩（MVIC）的20%。在NMES和NMES + ISO条件下，将NMES施加于胫骨前肌（TA）。在每个实验条件结束后，立即进行稳定的力量匹配收缩，强度为10% MVIC，同时使用高密度表面肌电图（HDsEMG）记录TA的肌电活动。从分解后的HDsEMG信号中分析运动单位放电率（DR）和峰间期变异性（ISIvar）。进行相干分析以评估不同频段共同突触输入的强度以及脊髓运动神经元接收的共同突触输入比例（pCSI）。使用力量变异系数（Force）评估力量稳定性。
与基线和干预后的NMES相比，NMES + ISO显著提高了运动单位DR。与基线、ISO和NMES相比，NMES + ISO还诱导pCSI增加。与所有实验条件相比，NMES + ISO后力量降低，表明力量稳定性得到改善。
这些结果表明，将NMES叠加到自主收缩上可以在低力量水平下提高运动单位放电率和pCSI。这些适应性变化似乎对力量稳定性有积极贡献，可能是通过激活过滤机制，将影响运动控制的独立突触噪声降至最低。这些发现为NMES运动诱导的适应性变化提供了新的视角，突出了一些涉及的神经生理机制，并丰富了我们对神经肌肉系统如何响应和适应基于NMES的干预措施的认识。
