Abstract
PURPOSE: The purposes of the present study were to: 1) apply the Dmax method to the amplitude domain of the electromyographic (EMG) signal to estimate the Dmax-EMG; and 2) compare the mean VO2 values at the Dmax-EMG, gas exchange (Dmax-GET), and ventilatory (Dmax-VT) thresholds. METHODS: Ten subjects (4 men and 6 women; mean ± SD age = 21.2 ± 2.9 yrs) performed an incremental cycle ergomter test to exhaustion. Oxygen consumption rate (VO2) and EMG signals from the vastus lateralis were recorded. The EMG amplitude (rms) values were calculated by averaging the last three complete pedal bursts of each power output. The Dmax-GET (VCO2 vs. VO2), Dmax-VT (VE vs. VO2) and Dmax-EMG (EMG amplitude vs. VO2) were determined as the point on the third order polynomial regression that measured the maximal perpendicular distance from the line between the first and last data points. A one-way repeated measures ANOVA was used to examine mean differences between Dmax-GET, Dmax-VT, and Dmax-EMG. In addition, Pearson product moment correlations were used to determine the relationships among the thresholds. RESULTS: The results of the present study indicated that there were no significant mean differences (p > 0.05) among the VO2 values for the Dmax-EMG (2.21 ± 0.48 L·min-1), Dmax- GET (2.34 ± 0.57 L·min-1), and Dmax-VT (2.38 ± 0.63 L·min-1). Furthermore, significant correlations were found among the Dmax-EMG vs. Dmax-GET (r = 0.86), Dmax-EMG vs. Dmax-VT (r = 0.83), and Dmax-GET vs. Dmax-VT (r = 0.99). CONCLUSION: The non-significant difference among Dmax-EMG, Dmax-GET, and Dmax-VT suggested that the Dmax method can be applied to the amplitude content of the EMG signal. Furthermore, these data suggested that the Dmax-EMG threshold may provide an alternative approach to demarcate the moderate from heavy exercise intensity domains.
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