Estimating electromyographic and heart rate fatigue thresholds from a single treadmill test

INTRODUCTION

The purposes of this study were to (1) develop a fatigue threshold based on electromyography (EMG) and heart rate (HR) responses for treadmill running from a single incremental test; and (2) propose a new fatigue threshold called the RV(EMGFT) and RV(HRFT).

METHODS

Eleven men performed incremental treadmill exercise to exhaustion on a single occasion. The RV(EMGFT) and RV(HRFT) were defined as the average of the highest velocity that resulted in a nonsignificant slope coefficient for the EMG amplitude versus time relationship and the lowest velocity that resulted in a significant positive slope coefficient.

RESULTS

There was a significant (P < 0.05) difference between the 2 thresholds [RV(EMGFT) = 11.7 ± 0.6 km/h and RV(HRFT) = 8.3 ± 0.8 km/h].

CONCLUSIONS

The fatigue threshold for EMG amplitude and heart rate can be determined from a single incremental treadmill test, but there are differences between cardiac and neuromuscular factors of fatigue.

Estimated times to exhaustion and power outputs at the gas exchange threshold, physical working capacity at the rating of perceived exertion threshold, and respiratory compensation point

The purposes of this study were to compare the power outputs and estimated times to exhaustion (Tlim) at the gas exchange threshold (GET), physical working capacity at the rating of perceived exertion threshold (PWCRPE), and respiratory compensation point (RCP). Three male and 5 female subjects (mean ± SD: age, 22.4 ± 2.8 years) performed an incremental test to exhaustion on an electronically braked cycle ergometer to determine peak oxygen consumption rate, GET, and RCP. The PWCRPE was determined from ratings of perceived exertion data recorded during 3 continuous workbouts to exhaustion. The estimated Tlim values for each subject at GET, PWCRPE, and RCP were determined from power curve analyses (Tlim = axb). The results indicated that the PWCRPE (176 ± 55 W) was not significantly different from RCP (181 ± 54 W); however, GET (155 ± 42 W) was significantly less than PWCRPE and RCP. The estimated Tlim for the GET (26.1 ± 9.8 min) was significantly greater than PWCRPE (14.6 ± 5.6 min) and RCP (11.2 ± 3.1 min). The PWCRPE occurred at a mean power output that was 13.5% greater than the GET and, therefore, it is likely that the perception of effort is not driven by the same mechanism that underlies the GET (i.e., lactate buffering). Furthermore, the PWCRPE and RCP were not significantly different and, therefore, these thresholds may be associated with the same mechanisms of fatigue, such as increased levels of interstitial and (or) arterial [K+].

The utility of electromyography and mechanomyography for assessing neuromuscular function: a noninvasive approach

This article introduces the utility of electromyography (EMG) and mechanomyography (MMG) for the assessment of neuromuscular function, and discusses the interpretation of the EMG and MMG signals for various exercise perturbations. The results of these studies suggest that the use of EMG and MMG to determine muscle fatigue is robust. Future studies with clinical populations are needed, however, to determine the optimal use of EMG and/or MMG for assessing muscle function in rehabilitative settings.

Oxygen uptake, heart rate, and ratings of perceived exertion at the PWCVo2

The purpose of the present study was to examine the oxygen uptake (Vo2), heart rate (HR), and ratings of perceived exertion (RPE [OMNI-Leg 0-10]) responses during continuous 1-hour cycle ergometer rides at the PWCVo2 (physical working capacity at the oxygen consumption threshold). Eight subjects (mean age +/- SD = 23 +/- 3.2 years) performed a maximal test to exhaustion for the determination of Vo2peak and ventilatory threshold (VT). The subjects also performed 4 randomly ordered 8-minute workbouts at different power outputs (ranging from 84 to 245 W) to determine the PWCVo2 and a continuous 1-hour cycle ergometer ride at the PWCVo2 during which Vo2, HR, and RPE data were collected every 2 minutes. The PWCVo2 (114 +/- 39 W) and VT (133 +/- 44 W) were not significantly different and occurred at 56 and 63% Vo2peak, respectively. Linear regression showed that the slope coefficients for the Vo2, HR, and RPE vs. time relationships for the continuous 1-hour workbouts were significantly greater than zero. Furthermore, a t-test about a single mean indicated that the mean slope coefficient for the HR vs. time relationship was significantly greater than 0.1 bpm x min(-1) (the rate of increase in HR that can be maintained for an 8-hour day). The results of this study indicated that PWCVo2 could be maintained for an extended period. However, the maximal power output associated with steady state Vo2, HR, and RPE responses was overestimated. The mean increase in Vo2 during the continuous 1-hour ride was 270 mL, which suggested that the PWCVo2 may demarcate the moderate from heavy exercise domains. The mean HR slope coefficient of 0.3 bpm x min(-1) indicated that the power output at the PWCVo2 could likely be maintained for greater than 2 hours.