Effects of exercise-induced muscle fatigue on VO2 slow component during heavy constant load exercise

BACKGROUND: The purpose of this study was to determine the relationship between the (V)over dotO(2) slow component and muscle fatigue estimated by isometric-maximal-knee-extension (IMKE) performed immediately after heavy-constant -load exercise (HCE). METHODS: Seven subjects performed HCE for three different exercise (3, 6 and 9 minutes) at a work rate corresponding to 50% of the difference between the V. O(2)peak and ventilatory threshold. Gas exchange variables were derived breath-by -breath. Electromyography was recorded from the vastus-lateralis (VL), rectus femoris (RF) and vastus medialis (VM) muscles, and integrated (iEMG) and mean power frequency (MPF) were calculated in HCE and IMKE. RESULTS: The amplitude of the (V)over dotO2 slow component was 371.4 +/- 109.9 mL/min. iEMG in the VL and VM during HCE was not changed. Although iEMG in the RF at 6 min was significantly increased, the increase of iEMG in the RF is not clearly concomitant with onset of the (V)over dotO2 slow component. The force output in IMKE after HCE significantly decreased. CONCLUSIONS: There was a significant correlation between decreasing rate of force output and increase in amplitude of the (V)over dotO(2) slow component. However, iEMG and MPF in IMKE did not significantly change. Thus, these results suggest that the (V)over dotO2 slow component is induced by muscle fatigue which changes the muscle contraction process after muscle electric discharge.