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The purposes of this investigation were twofold: (1) to determine if the model used for estimating the physical working capacity at the fatigue threshold (PWC^sub FT^) from electromyographic (EMG) amplitude data could be applied to the frequency domain of the signal to derive a new fatigue threshold for cycle ergometry called the mean power frequency fatigue threshold (MPF^sub FT^), and (2) to compare the power outputs associated with the PWC^sub FT^, MPF^sub FT^, ventilatory threshold (VT), and respiratory compensation point (RCP). Sixteen men [mean (SD) age = 23.4 (3.2) years] performed incremental cycle ergometer rides to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. There were significant (p < 0.05) mean differences for PWC^sub FT^ [mean (SD) = 168 (36) W] versus MPF^sub FT^ [208 (37) W] and VT [152 (33) W] versus RCP [205 (84) W], but no mean differences for PWC^sub FT^ versus VT or MPF^sub FT^ versus RCP. The mean difference between PWC^sub FT^ and MPF^sub FT^ may be due to the effects of specific metabolites that independently influence the time and frequency domains of the EMG signal. These findings indicated that the PWC^sub FT^ model could be applied to the frequency domain of the EMG signal to estimate MPF^sub FT^. Furthermore, the current findings suggested that the PWC^sub FT^ may demarcate the moderate from heavy exercise domains, while the MPF^sub FT^ demarcates heavy from severe exercise intensities.[PUBLICATION ABSTRACT]