A New Mechanomyographic Amplitude-Based Fatigue Threshold Test for Cycling

Abstract

PURPOSE: The purposes of this study were to: a) apply the Dmax method previously used to determine the gas exchange threshold (GET) to the amplitude content of the mechanomyographic (MMG) signal to estimate the Dmax-MMG threshold; and b) compare the mean VO2 values from the Dmax-MMG, GET, and respiratory compensation point (RCP) during incremental cycle ergometry. METHODS: Ten males (mean ± SD age = 23.3 ± 3.7 yrs) performed an incremental cycle ergometer test to exhaustion. MMG signals from the vastus lateralis and VO2 were recorded. The contraction period for each pedal thrust (descending phase of the pedaling cycle) was determined from the MMG bursts. The GET and RCP values were determined by non-invasive gas exchange measurements using the V-slope method and defined as the VO2 value corresponding to the intersection of two linear regression lines derived separately from the data points below and above the breakpoints for the VCO2 vs. VO2, and VE vs. VCO2 relationships, respectively. The MMG amplitude (rms expressed in m·s2) values were calculated by averaging the last three complete pedal thrusts of each power output. The Dmax-MMG (i.e., MMG vs.VO2) was determined as the point on the third order polynomial regression curve that yielded the maximal perpendicular distance to the straight line formed by the first and the last data points. A one-way repeated measures ANOVA and Tukey post-hoc comparisons were used for mean comparison among thresholds. Pearson product moment correlations were used to determine the relationships among the three fatigue thresholds. RESULTS: The results of the present study indicated that the mean VO2 for the RCP (3.22 ± 0.22 L·min-1) was significantly greater (p < 0.05) than the GET (2.43 ± 0.26 L·min-1) and Dmax-MMG (2.63 ± 0.48 L·min-1). There was no significant difference, however, between the mean VO2 for the GET and Dmax-MMG. Furthermore, there were no significant correlations for the Dmax-MMG vs. GET (r = -0.29), Dmax-MMG vs. RCP (r = -0.04), or GET vs. RCP (r = 0.49). CONCLUSIONS: The non-significant mean difference between the GET and Dmax-MMG suggested that these thresholds may reflect a similar dimension of metabolic and neuromuscular fatigue. It is possible that like the GET, the Dmax-MMG demarcates the moderate from heavy exercise intensity domains.