Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland.
Faculty of Health, School of Exercise and Nutrition Sciences, Institute for Physical Activity and Nutrition (IPAN), Deakin University, Geelong, Australia.
Eur J Appl Physiol. 2024 Nov;124(11):3377-3386. doi: 10.1007/s00421-024-05538-8. Epub 2024 Jun 28.
To assess the effect of a remote handgrip contraction during wide-pulse high-frequency (WPHF) neuromuscular electrical stimulation (NMES) on the magnitude of extra torque, progressive increase in torque during stimulation, and estimates of the persistent inward current (PIC) contribution to motoneuron firing in the plantar flexors.
Ten participants performed triangular shaped contractions to 20% of maximal plantar flexion torque before and after WPHF NMES with and without a handgrip contraction, and control conditions. Extra torque, the relative difference between the initial and final torque during stimulation, and sustained electromyographic (EMG) activity were assessed. High-density EMG was recorded during triangular shaped contractions to calculate ∆F, an estimate of PIC contribution to motoneuron firing, and its variation before vs after the intervention referred to as ∆F change score.
While extra torque was not significantly increased with remote contraction (WPHF + remote) vs WPHF (+ 37 ± 63%, p = 0.112), sustained EMG activity was higher in this condition than WPHF (+ 3.9 ± 4.3% MVC EMG, p = 0.017). Moreover, ∆F was greater (+ 0.35 ± 0.30 Hz) with WPHF + remote than control (+ 0.03 ± 0.1 Hz, p = 0.028). A positive correlation was found between ∆F change score and extra torque in the WPHF + remote (r = 0.862, p = 0.006).
The findings suggest that the addition of remote muscle contraction to WPHF NMES enhances the central contribution to torque production, which may be related to an increased PIC contribution to motoneuron firing. Gaining a better understanding of these mechanisms should enable NMES intervention optimization in clinical and rehabilitation settings, improving neuromuscular function in clinical populations.
评估在宽脉冲高频（WPHF）神经肌肉电刺激（NMES）期间进行远程手部握力收缩对额外扭矩的幅度、刺激过程中扭矩的逐渐增加以及对内向电流（PIC）对足底屈肌运动神经元放电贡献的估计的影响。
10 名参与者在 WPHF NMES 之前和之后进行了 20%最大足底屈曲扭矩的三角形收缩，分别有和没有手部握力收缩，以及控制条件。评估了额外扭矩、刺激过程中初始和最终扭矩之间的相对差异以及持续肌电图（EMG）活动。在三角形收缩期间记录高密度 EMG，以计算 ∆F，这是 PIC 对运动神经元放电贡献的估计值，以及干预前后的变化，称为 ∆F 变化分数。
虽然与 WPHF（+37±63%，p=0.112）相比，远程收缩（WPHF+远程）并没有显著增加额外扭矩，但在这种情况下，持续的 EMG 活动高于 WPHF（+3.9±4.3%MVC EMG，p=0.017）。此外，与对照组（+0.03±0.1Hz）相比，WPHF+远程时 ∆F 更大（+0.35±0.30Hz，p=0.028）。在 WPHF+远程中，发现 ∆F 变化分数与额外扭矩之间存在正相关（r=0.862，p=0.006）。
研究结果表明，将远程肌肉收缩添加到 WPHF NMES 中可以增强对扭矩产生的中枢贡献，这可能与 PIC 对运动神经元放电贡献的增加有关。更好地了解这些机制应能优化 NMES 干预在临床和康复环境中的应用，从而改善临床人群的神经肌肉功能。
