5 years ago

EMG amplitude, fatigue threshold, and time to task failure: A meta-analysis

Electromyographic (EMG) fatigue threshold (EMGFT) is a correlate of critical power and torque or force thresholds which establish theoretical exercise intensities below which neuromuscular fatigability is negligible and unpredictable. These thresholds are identified by the point where rate of change of EMG amplitude (ΔE M ¯ G) is zero. Recent studies provide evidence of neuromuscular fatigability below critical thresholds and raise questions about the construct validity of EMGFT. Objectives Evaluate the construct validity of EMGFT by aggregating ΔE M ¯ G and time to failure (Tlim) data from fatiguing isometric contractions. Methods Database searches of MEDLINE, SPORTDiscus, Web of Science, and Cochrane (inception–September 2016) were conducted using terms relevant to EMG and muscle fatigue. Inclusion criteria were studies reporting agonist muscle EMG amplitude data during constant force voluntary isometric contractions taken to task failure. Linear and nonlinear regression models were used to relate ΔE M ¯ G and Tlim data extracted from included studies. Results Regression analyses included data from 837 healthy adults and 44 studies. Correlations between ΔE M ¯ G and Tlim were strong in both nonlinear (R2 =0.65) and linear (R2 =0.82) models. ΔE M ¯ G at EMGFT was significantly nonzero overall and in 3 of 5 cohorts in the nonlinear model (p<0.01) and in 2 of 5 cohorts in the linear model. Conclusion EMGFT lacks face validity as currently calculated; models for more precise EMGFT calculation and prediction of task failure using EMG amplitude alone are proposed. The correlation between EMG amplitude change rate and Tlim is shown to remain consistent across sexes and force vs. position tasks.

Publisher URL: www.sciencedirect.com/science

DOI: S1440244017317619

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