ELECTROMYOGRAPHIC, MECHANOMYOGRAPHIC, AND HEART RATE RESPONSES AT CRITICAL POWER

Abstract

726 The purpose of the present study was to determine the electromyographic (EMG), mechanomyographic (MMG), and heart rate (HR) responses to cycle ergomertry at the critical power (CP). Seven healthy males (25 ± 3 yrs) performed an incremental test to exhaustion and five or six workbouts at power outputs ranging from peak power (Ppeak)-100 watts (W) to Ppeak + 50 W, to estimate CP. Each subject then completed a 60 min trial at their CP estimated from the nonlinear, 3 parameter regression model (Non-3) of Morton (Ergonomics 39: 611-619, 1996). EMG (μ Vrms) and MMG (m Vrms) amplitudes were recorded from the vastus lateralis every 3 minutes using a bipolar surface electrode and piezoelectric crystal contact sensor arrangement. HR was recorded using a cardiomonitor system. The results indicated that the mean CP was 175 ± 23 W, which represented 58 ± 5% of the Ppeak. Mean HR increased significantly (P<0.05) over the 60 min. The slope of the mean EMG amplitude versus time relationship was not significantly (P>0.05) different from zero however, the mean MMG amplitude decreased significantly (P<0.001) over the 60 min. These findings indicated that there were dissociations between the mechanical aspects of muscle activity (MMG) and both the electrical activity (EMG) and HR during 60 min of cycle ergomertry at the CP. CP has previously been shown to overestimate a long-term maintainable workload, and although these subjects completed 60 min at CP, their HR values were 93 ± 5% of HRpeak at 60 min. The dissociation between EMG and MMG during the continuous trials may have been related to "muscle wisdom" or changes in muscle temperature and/or fluid volume.