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The purposes of this study were twofold: 1 ) to derive the mechanomyographic mean power frequency fatigue threshold (MMG MPFFT) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPFFT to other neuromuscular and gas exchange fatigue thresholds. 9 adults (5 men and 4 women; mean±SD age = 23.7±3.7 years; body weight = 66.3 ±8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the fatigue threshold (PWCFT), MMG MPFFT, and gas exchange threshold (GET) suggested that different physiological mechanisms may underlie these 3 fatigue thresholds. A significant correlation (r = 0.83) for the MPFFT vs. respiratory compensation point (RCP) suggested that these fatigue thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWCFT (mean±SD=163±43 W), MMG MPFFT (132 ±33 W), and GET (144±28 W) than MPFFT ( 196±53 W) and RCP (202±41 W) suggested that these gas exchange and neuromuscular fatigue thresholds may demarcate different exercise intensity domains. [ABSTRACT FROM AUTHOR]