2003 Volume 1 Issue 1 Pages 9-18
The rate of increase in oxygen uptake (VO2) at the onset of a bout of heavy exercise is faster if it is preceded by a similar bout of heavy exercise. We tested the hypothesis during heavy leg exercise that leg blood flow (LBF) and VO2 would both be elevated during the adaptive phase. On three separate days, six healthy young men completed two bouts of 6-minutes of knee extension / flexion exercise at about 85% VO2peak separated by 5-minutes 0-watt exercise on an electrically braked ergometer. LBF was determined by Doppler ultrasound. In the second exercise bout, LBF and VO2 were significantly elevated in the baseline before exercise and throughout the exercise. Both the mean response time (time to 63% of difference between baseline and calculated end value) and the difference in VO2 between minutes 3 and 6 of exercise indicated significantly faster attainment of the end exercise value in the second heavy exercise bout. These data showing the elevated LBF in the second bout of heavy exercise support the link between O2 delivery and the adaptation of oxidative metabolism at the onset of heavy exercise.