本篇研究觀察人體股四頭肌接受電刺激時，當它被擺在伸長或縮短的位置時肌肉疲勞的情形，利用誘發肌電訊號觀察肌肉活性，而誘發肌電訊號的特徵觀察包含峰對峰值、達峰值時間與峰對峰間隔時間，這些量測值隨著疲勞的過程所形成的曲線，經由雙曲線正切函數的曲線近似便可以取出時間常數、轉折點及相對剩餘值。
　　為了驗證實驗的觀察，本篇研究建構一誘發肌電訊號的數學模型以模擬疲勞的過程，這種結構性的肌電訊號模型考量運動單元的數量、形式及電極與運動單元領域距離來模擬誘發肌電訊號。以不同組成的慢速(型一)與快速(型二)肌肉纖維。誘發肌電訊號是以不同比例的型一與型二肌肉纖維所產生的運動單元動作電位的加成所形成，以非線性的最佳化技術從誘發肌電訊號中粹取型一與型二肌肉纖維的振幅與時間特徵，先以模擬的訊號來驗證特徵粹取的演算法。
　　實驗結果顯示肌肉在較短的位置時，力量輸出與肌電訊號的時間常數及轉折點都比肌肉在較長的位置時大，這顯示肌肉在較長的位置時接受電刺激疲勞的較早也較快，這也可以從肌電圖的特徵與力量曲線中觀察得到。結論：由數學模型可以發現肌肉在較長位置時的易疲勞與型二肌肉纖維的快速耗盡有關，本研究證實了此數學模型用於肌肉疲勞研究中觀察重要生理參數的可行性。

　　This study compared the different fatigue processes of electrically elicited muscle contractions of rectus femoris in both lengthened and shortened positions. Stimulus-evoked electromyography (EMG), after artifact suppression, was used to observe the fatigue process. The measured EMG features included peak to peak amplitude, rise time to peak, and peak to peak duration. The measurements were fitted by a hyperbolic tangent function, which allowed the observation of their time constants, inflection times and relative residual levels during the fatigue process. To verify the observation from experiment, a mathematical model of the evoked EMG was constructed to simulate the changes of EMG features during the fatigue process. A structured model considering the numbers and types of MU and the electrode-motor unit territory distance was utilized to simulate stimulus-evoked EMG. The evoked EMG was simulated by summing up the MUAPs generated from different proportions of fast-twitch or slow-twitch muscle fibers. A nonlinear optimization technique was utilized to extract amplitude and duration features of type I and type II MUs from the stimulus-evoked EMG. The experimental results show that the time constants of torque output and EMG temporal features as well as the inflection time measured in the shortened positions are larger than those in the lengthened position. These evidences indicate that electrically elicited muscle contraction in lengthened position is prone to fatigue earlier and faster. Furthermore, the mathematical modeling reveals that the early fatigue in the lengthened muscles was resulted from the fast depletion of the type II MU. Our study confirms the feasibility of using this mathematical model to observe the important physiological changes from the evoked EMG.

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