Fatiguing effects of indirect vibration stimulation in upper limb muscles- post and during isometric contractions superimposed on upper limb vibration

Whole body vibration and upper limb vibration (ULV), continues to gain popularity as exercise intervention for rehabilitation and sports applications. However, the fatiguing effects of indirect vibration stimulation are not yet fully understood. We investigated the effects of ULV stimulation superimposed on fatiguing isometric contractions using a purpose developed upper limb stimulation device. Thirteen healthy volunteers were exposed to both ULV superimposed to fatiguing isometric contractions (V) and isometric contractions alone- Control (C). Both Vibration (V) and Control (C) exercises were performed at 80% of the maximum voluntary contractions. The stimulation used was 30 Hz frequency of 0.4 mm amplitude. Surface-electromyographic (EMG) activity of the Biceps Brachii, Triceps Brachii, and Flexor Carpi Radialis were measured. EMG amplitude (EMGrms) and mean frequency (MEF) were computed to quantify muscle activity and fatigue levels. All muscles displayed significantly higher reduction in MEFs and corresponding significant increase in EMGrms with the V than the Control, during fatiguing contractions (P < 0.05). Post vibration, all muscles showed higher levels of MEFs after recovery compared to the control. Our results show that near maximal isometric fatiguing contractions superimposed on vibration stimulation lead to a higher rate of fatigue development compared to the isometric contraction alone in the upper limb muscles. Results also show higher manifestation of mechanical fatigue post treatment with vibration compared to the control. Vibration superimposed on isometric contraction not only seems to alter the neuromuscular function during fatiguing efforts by inducing higher neuromuscular load but also post vibration treatment.

全身振动与上肢振动（Upper Limb Vibration, ULV）作为康复及运动领域的干预手段，正持续受到广泛关注。然而，间接振动刺激的疲劳效应尚未被完全阐明。本研究采用自主研发的上肢刺激装置，探究了叠加于疲劳性等长收缩的ULV刺激效应。招募13名健康志愿者，分别完成两组实验方案：一组为叠加ULV的疲劳性等长收缩组（简称V组），另一组为单纯疲劳性等长收缩的对照组（简称C组）。两组实验均以最大自主收缩量的80%强度进行。本次实验采用的振动刺激参数为：频率30Hz，振幅0.4mm。研究采集了肱二头肌、肱三头肌及桡侧腕屈肌的表面肌电图（Surface-electromyographic, EMG）信号，并通过计算肌电均方根振幅（EMG root mean square, EMGrms）与平均频率（Mean Frequency, MEF），量化肌肉活动水平与疲劳程度。在疲劳性收缩过程中，V组各肌肉的MEF降幅显著高于C组，同时EMGrms增幅亦显著高于C组（P < 0.05）。振动刺激结束后，所有肌肉在恢复期的MEF水平均高于对照组。本研究结果表明，在上肢肌肉中，叠加振动刺激的接近最大强度的疲劳性等长收缩，相较于单纯等长收缩，会导致更快的疲劳进展速度。同时，实验结果还显示，振动刺激组在干预后表现出比对照组更为显著的机械疲劳表征。叠加于等长收缩的振动刺激，不仅可通过提升神经肌肉负荷，改变疲劳过程中的神经肌肉功能，还会对振动刺激后的恢复阶段产生影响。