A single electromyographic testing point is valid to monitor neuromuscular fatigue during continuous exercise

Two different protocols for estimating the electromyographic fatigue threshold (EMGFT) have been proposed in the literature. These protocols are distinguished by the number of visits required to determine the EMGFT. The purpose of this study, therefore, was to statistically compare the estimated EMGFT from the single-visit incremental test and the multiple-visit constant workload tests for single-leg knee-extensor exercise. Seven healthy college-aged men [mean ± SEM; age = 25.0 ± 0.7 years] performed the incremental test and on separate occasions also performed 4 constant workload tests to voluntary exhaustion. The EMG amplitude was recorded from the rectus femoris muscle during all the testing sessions. For the single-visit test, the EMG amplitude vs. time relationship for each power output was examined using linear regression. For the multiple-visit tests, the EMG amplitude vs. time relationship was calculated for each constant power output. Thereafter, the power outputs were plotted as a function of the slope coefficient for the EMG amplitude vs. time relationships, and linear regression was performed. The EMGFT was defined as the intersection of the regression line with the y-intercept of the power output vs. slope coefficient plot. The results indicated that the estimated EMGFT from the single-visit test was significantly (p = 0.012) lower than the estimate from the multiple-visit tests. Because this test is performed during a single visit and concludes within 20 minutes, it may also have application in clinical rehabilitation settings and not merely for an athletic population.