Determination of maximal power output at neuromuscular fatigue threshold.

The purpose of this study was to determine the maximal power output at the neuromuscular fatigue threshold (EMGFT), as estimated from electromyographic (EMG) data from representative leg muscles during cycling. The rate of rise in integrated EMG activity as a function of time (iEMG slope) was calculated at each of four constant-power-output ergometer bouts for 20 subjects. The iEMG slopes were plotted against work rates that were well described as linear functions (0.84 < R2 < 0.99). This iEMG slope vs. work rate relationship was extrapolated to zero slope to give an intercept on the power axis that was interpreted as the highest work rate sustainable without EMG evidence of neuromuscular fatigue (EMGFT). Each individual EMGFT was then expressed in terms of an O2 output (VO2) equivalent on the basis of the individual delta efficiency calculated during a linearly increasing maximal exercise test on the same bicycle ergometer. Results indicated a highly significant correlation (r = 0.92, P < 0.01) between EMGFT VO2 and anaerobic threshold VO2, as determined by conventional gas exchange criteria. The mean EMGFT VO2 (1.84 +/- 0.55 l/min) was, however, significantly greater (P < 0.01) than the anaerobic threshold VO2 (1.72 +/- 0.54 l/min). It was suggested that the EMGFT may provide an attractive alternative to the measurement of the highest work rate that can be sustained without evidence of neuromuscular fatigue.