PURPOSE: This study examined the patterns of responses for electromyographic amplitude (EMG RMS), EMG mean power frequency (EMG MPF), mechanomyographic amplitude (MMG RMS), MMG MPF, oxygen consumption rate (O2), and power output (PO) during sustained cycle ergometry at a constant rating of perceived exertion (RPE). METHODS: Ten subjects (mean ± SD; age= 21.1 ± 2.1 yr; body mass= 70.3 ± 13.6 kg) performed an incremental cycling test to exhaustion to determine peak values for each variable. On separate days, each subject completed 4, 8-min submaximal (65-80% O2peak) rides to determine the physical working capacity at the OMNI RPE threshold (PWCOMNI). On the final visit,EMG RMS, EMG MPF, MMG RMS, MMG MPF, O2, and PO were recorded during a 1 hr ride at a constant RPE that corresponded to the PWCOMNI. RESULTS: The mean (± SD), normalized EMG RMS, EMG MPF, MMG RMS, MMG MPF, O2, and PO values at min 10 and min 60 of the 1 hr rides were, 51 ± 17 and 48 ± 26% EMG RMSpeak, 118 ± 17 and 121 ± 21% EMG MPFpeak, 67 ± 15 and 71 ± 11% MMG RMSpeak, 122 ± 45 and 114 ± 39% MMG MPFpeak, 57 ± 5 and 51 ± 11% O2peak, and 52 ± 35 and 38 ± 33% POpeak, respectively. There were significant, negative, linear relationships for EMG RMS (r2 =0.67) and MMG MPF (r2 =0.20) versus time during the 1 hr rides. There were no changes over time, however, for EMG MPF, MMG RMS, or RPE. In addition, there were significant, negative, quadratic relationships for (R2 = 0.90) and PO (R2 = 0.99) versus time. CONCLUSION: EMG RMS and MMG MPF tracked the decreases in and PO during the constant RPE rides, while EMG MPF and MMG RMS, remained unchanged and tracked RPE. The decreases in EMG RMS and MMG MPF were likely attributable to a decrease in motor unit firing rate, while the lack of change in MMG RMS may have been the result of a balance between the de-recruitment of fast twitch fibers as PO decreased, which tends to decrease MMG RMS, and an increase in the ability of activated fibers to oscillate, which tends to increase MMG RMS. These findings indicated that during submaximal cycle ergometry at a constant RPE, fast twitch fiber recruitment and mechanical changes within the working muscle may influence the perception of effort via feedback from type III and IV afferents to the central nervous system.