研究目的：所謂肌肉疲勞(muscle fatigue)是指因運動導致肌肉收縮能力降低或無法維持穩定的力量。儘管肌肉疲勞的機制相當複雜且擁有多面向的特徵，過去大部分的研究都只著重在作用肌肉本身生理特性的改變，而較少注意到隨著肌肉疲勞產生，疲勞引起的肢體微振動的變化。本研究結合肌電訊號、施力波動以及肢體微振動訊號，來描述持續性的25%以及75%最大自主收縮力量等長收縮過程中肌肉疲勞特徵的變化。因此本實驗的研究目的為：(1)比較兩種不同施力程度的疲勞性收縮之下，施力震顫(包含施力波動以及肢體微振動)特徵隨著時間進展的變化差異；(2)比較施力波動與肢體微振動訊號以及肌電訊號在反應肌肉疲勞變化上的差異，以對肌肉疲勞的生理特性有更進一步的瞭解。

　　研究方法：十五位健康成人參與本研究，主要任務為執行持續性的食指外展等長性收縮直到精疲力竭為止，施力程度為75%(高強度)以及25%(低強度)最大自主收縮力量(MVC)。過程中收集受試者的施力波動、背側第一掌骨間肌(FDI)的肌電訊號以及食指指節和手部微振動訊號的變化。分析的參數包括施力波動、肌電訊號以及肢體微振動訊號的均方根值、頻譜高峰頻率、主要頻帶頻譜功率以及肌電訊號中頻從0%到100%耐力限制時間點的變化。掌骨-指骨間關節的機械耦合強度在肌肉疲勞時的變化則以近端指節與掌骨微振動訊號的相關性來呈現。另外還會分析微振動-肌電訊號、微振動-施力波動訊號以及肌電-施力波動訊號互譜值於兩種不同疲勞收縮過程中的變化，來不同生理訊號之間的一致性變化。

　　研究結果：施力波動，肌電訊號以及微振動訊號均方根值在兩種施力強度的疲勞收縮下隨著時間都有明顯的上昇，且以微振動訊號在低程度收縮時相對於起始值的上升幅度最為顯著。指節與手部微振動訊號的相關性在低程度收縮時是逐漸上升的，反之高程度收縮時則逐漸下降。肌電訊號中頻下降趨勢則以高程度收縮較為顯著。微振動訊號頻譜的高峰頻率主要落在8-12 Hz以及20-40 Hz兩個頻帶內，低程度收縮時高峰頻率會由8.72上升到10.48 Hz，而不論施力程度兩個頻帶的頻譜功率皆顯著上升，尤其以低程度收縮的上升幅度最為明顯。訊號間互譜值方面，震顫-肌電訊號有8-12 Hz以及20-30 Hz兩個頻帶的互譜值達顯著水準，而震顫-施力訊號以及肌電-施力訊號只有在8-12 Hz有顯著相關，訊號間互譜值的變化趨勢受到施力程度高低相當大的影響：高程度收縮時，所有訊號組合以及頻帶的互譜值都明顯下降，低程度收縮時，除了震顫-肌電訊號在20-30Hz頻帶的互譜值維持在顯著水準不變之外，其他的互譜值隨著肌肉疲勞都有明顯的上升趨勢。

　　結論：施力波動、肌電訊號以及肢體微振動訊號在肌肉疲勞性收縮過程的特徵變化會因為施力程度不同而有差異，可能是由於不同施力程度所造成動作單元活動徵召與去徵召的差異；其中，肢體微振動訊號比其他生理訊號似乎提供更多額外的關於肌肉疲勞的特徵，因為肢體微振動訊號能更完整地反映出包含肌肉機械特性、反射敏感度以及中樞神經振盪等與肌肉疲勞有關的特徵變化。

　　Objective: Muscle fatigue has been defined as exercise-induced reduction in the ability of a muscle to generate force or power. Despite complexity of underlying mechanisms and multi-facet features of muscle fatigue, little attention has been paid to exhaustion-driven microvibration that steps up in association with fatigue development. In this study, we combined EMG, force fluctuations, and limb microvibrations to characterize fatigue development in the course of sustained isometric contraction at 25% and 75 % maximal voluntary contractions (MVC). The purposes of this study are: 1) to contrast temporal changes in force tremors (force fluctuations and limb microvibrations) between fatiguing isometric contractions at the two exertion levels, and 2) to compare differences of muscle fatigue characterized with force fluctuations, limb microvibrations, and surface EMG to gain a better insight into fatigue physiology.

　　Methods: Fifteen healthy adult volunteers performed sustained isometric index abduction at 25% and 75% MVC until exhaustion. Force fluctuations, electromyographic (EMG) activities of the first dorsal interosseous (FDI) and limb microvibrations from the index and the hand were recorded. A number of temporal alternation in fatigue-related parameters were assessed, including root mean square (RMS) of EMG, force fluctuations, and limb microvibrations, spectral power and spectral peaks of force tremors, EMG median frequency (MDF) from 0% to 100% endurance of limits. The fatigue-related changes in strength of mechanical coupling of the metacarpal-phalangeal (MCP) joint were quantified with correlation between microvibrations of proximal phalange and metacarpal bone. Coherence of microvibration-EMG (CohMV-EMG), microvibration-force fluctuation (CohMV-FF), and EMG-force fluctuation (CohEMG-FF) were calculated to substantiate community changes among different physiological signals resulted from two different fatigue processes.

　　Results: Force fluctuations, EMG RMS and microvibrations increased progressively with time during 25% and 75% MVC fatiguing contractions, with the most remarkable increment for microvibration in reference to its initial value at the low force level (25%MVC) contraction. Correlation of microvibrations between the finger and the hand increased progressively at the low force level contraction, however, the correlation reduced together with EMG MDF at the high force level contraction (75% MVC). Spectral analysis of microvibrations demonstrated that two marked spectral peaks in 8-12 and 20-40 Hz bands. Spectral peaks of microvibrations in 8-12 Hz band increased from 8.72 to 10.48 Hz after low level fatiguing contraction. Besides, spectral power within those two main frequency bands increased significantly, with more obvious trend during the low level fatiguing contraction. As for coherence, there were 8-12 Hz and 20-30 Hz in the CohMV-EMG, but only the 8-12 Hz rhythms were present in the CohMV-FF and CohEMG-FF. Coherence were subject to the levels of fatiguing contraction. At the high level fatiguing contraction, coherence of all the combinations and frequency bands declined drastically with fatigue. Comparatively, at the low level fatiguing contraction, CohMV-EMG in the 20-30 Hz remained insensitive to fatigue progress, whereas CohMV-EMG, CohMV-FF and CohEMG-FF in the 8-12 Hz increased significantly with fatigue.

　　Conclusion: There were exertion-dependent changes in characteristics of force fluctuations, EMG, and limb microvibrations during fatiguing contractions. It might involve with different MU recruitment/ decruitment strategies between the two different exertion levels. In contrast to EMG and force fluctuation, limb microvibration appeared to provide more comprehensive pictures of fatigue development, because it reflects an integrated feature of fatigue-related changes in muscle mechanical properties, reflex sensitivity, and neural involvement as a result of central oscillation.

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