Research

The relationships among endurance performance measures as estimated from VO_2PEAK, ventilatory threshold, and electromyographic fatigue threshold: a relationship design

Jennifer L Graef^* , Abbie E Smith^* , Kristina L Kendall^* , Ashley A Walter^* , Jordan R Moon^* , Christopher M Lockwood^* , Travis W Beck^* , Joel T Cramer^* and Jeffrey R Stout

Department of Health and Exercise Science, University of Oklahoma, Huston Huffman Center, 1401 Asp Ave., Norman, OK 73019, USA

Dynamic Medicine 2008, 7:15doi:10.1186/1476-5918-7-15

Published:	10 September 2008

Abstract

Background

The use of surface electromyography has been accepted as a valid, non-invasive measure of neuromuscular fatigue. In particular, the electromyographic fatigue threshold test (EMG_FT) is a reliable submaximal tool to identify the onset of fatigue. This study examined the metabolic relationship between VO_2PEAK, ventilatory threshold (VT), and the EMG_FT, as well as compared the power output at VO_2PEAK, VT, and EMG_FT.

Methods

Thirty-eight college-aged males (mean ± SD = 22.5 ± 3.5 yrs) performed an incremental test to exhaustion on an electronically-braked cycle ergometer for the determination of VO_2PEAK and VT. Each subject also performed a discontinuous incremental cycle ergometer test to determine their EMG_FT value, determined from bipolar surface electrodes placed on the longitudinal axis of the vastus lateralis of the right thigh. Subjects completed a total of four, 2-minute work bouts (ranging from 75–325 W). Adequate rest was given between bouts to allow for subjects' heart rate to drop within 10 beats of their resting heart rate. The EMG amplitude was averaged over 10-second intervals and plotted over the 2-minute work bout. The resulting slopes from each successive work bout were used to calculate EMG_FT.

Results

Power outputs and VO₂ values from each subject's incremental test to exhaustion were regressed. The linear equations were used to compute the VO₂ value that corresponded to each fatigue threshold. Two separate one-way repeated measure ANOVAs indicated significant differences (p < 0.05) among metabolic parameters and power outputs. However, the mean metabolic values for VT (1.90 ± 0.50 l·min^-1) and EMG_FTVO₂(1.84 ± 0.53 l·min^-1) were not significantly different (p > 0.05) and were highly correlated (r = 0.750). Furthermore, the mean workload at VT was 130.7 ± 37.8 W compared with 134.1 ± 43.5 W at EMG_FT (p > 0.05) with a strong correlation between the two variables (r = 0.766).

Conclusion

Metabolic measurements, as well as the power outputs at VT and EMG_FT, were strongly correlated. The significant relationship between VT and EMG_FT suggests that both procedures may reflect similar physiological factors associated with the onset of fatigue. As a result of these findings, the EMG_FT test may provide an attractive alternative to estimating VT.