THE SLOW COMPONENT OF OXYGEN UPTAKE AND THE MEAN POWER FREQUENCY OF EMG DURING HEAW INTENSITY EXERCISE

Abstract

The purpose of this study was to elucidate the mechanisms causing the slow component of oxygen uptake (VO2), by investigating changes in exercising muscle electrical activity. Volunteers performed square-wave dynamic knee extension exercise. Surface EMG of the rectus femoris was used to measure mean power frequency (MPF) and integrated (IEMG) values for each contraction. VO2 was measured breath-by-breath using a mass spectrometer. During 'heavy' intensity exercise eliciting a VO2 slow component and muscle fatigue, there was no decrease in MPF, which contrasts with 'severe' exercise where the MPF decreased as muscle fatigue occurred. Results from this study suggest a change in fibre recruitment from slow-twitch to oxygen-inefficient high-frequency fasttwitch fibres during fatiguing exercise as the cause of the VO2 slow component.