The relation between critical power and neuromuscular fatigue as estimated from electromyographic data

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Abstract
The relation between critical power (CP) and the onset of fatigue (fatigue threshold or FT) was defined, as estimated from electromyographic [EMG] data taken from representative [huma] leg muscles during cycling. The rate of rise in integrated EMG (IEMG) activity as a function of time (IEMG slope) was calculated at each of 3 or 4 constant power output ergometer bouts for 11 subjects. The IEMG slopes so obtained were plotted against workload resulting in linear plots (0.88 < R2 < 0.99) which were extrapolated to 0 slope to give an intercept on the power axis which was interpreted as the fatigue threshold (FT). The mean workload at CP was 169.5 .+-. 12.8 W compared with 190.5 .+-. 14.0 W at FT (P < 0.05) though the 2 measurements were highly correlated. Power output at anaerobic threshold (AT) was not significantly different from FT at 187.1 .+-. 15.9 W. The correlation between these 2 variables was 0.903. The IEMG estimation of FT may provide an attractive alternative to the measurement of anaerobic threshold.