Effects of Moderate versus Variable High Intensity Cycling on Metabolic Responses During Recovery.

Abstract

PURPOSE: Examine oxygen consumption (VO2), energy expenditure and respiratory exchange ratio (RER) during recovery following moderate-intensity exercise (MIE) and variable high-intensity exercise (VIE) in healthy adults (n=5; age = 20.2 ± 5.7 yrs). METHODS: Two experimental conditions (MIE and VIE) were randomized and performed on separate days in the fasted state. Both conditions commenced with a 15-min seated rest, followed by the assigned exercise. MIE consisted of continuous moderate-intensity exercise at 40% of WRmax. VIE consisted of sixteen 10-sec supramaximal sprints (120% WRmax), sixteen 20-sec high intensity bouts (60% WRmax) and low-intensity recovery (20% WRmax) interspersed throughout the exercise. Total duration and total work were matched between conditions. Following exercise, there was 75 minutes of seated recovery. Resting VO2 was averaged over the final 10 min of rest. VO2 and respiratory exchange ratio (RER) were recorded during exercise and every 15-minutes of recovery. NetVO2 was calculated as the VO2 above resting VO2. Energy expenditure (EE) and fat oxidation rate (FatOx) were calculated. VO2 and RER responses between conditions were compared using a 2-way repeated measure ANOVAs and EE and FatOx between conditions were compared using paired t-tests. Significance was established if p≤0.05. RESULTS: During recovery, net VO2 decreased in both conditions from exercise (VIE = 1184.2 ± 247.0 ml·min-1; MIE = 1005.8 ± 222.1 ml·min-1) to 75 minutes (VIE = 40.3 ml·min-1 ± 23.6; MIE = 16.1 ± 10.2 ml·min-1). There were no differences in net VO2 between conditions during recovery. Net EE during recovery from VIE and MIE were 10.8 ± 6.7 kcals and 5.5 ± 3.9 kcals, respectively (p =0.13). During VIE and MIE, RER was 1.02 ± 0.4 and 0.96 ± 0.06, respectively (P=0.06). During recovery, RER was lower in VIE compared to MIE at 30 (0.81 ± 0.07 vs. 0.89 ± 0.07) and 45 minutes (0.85 ± 0.11 vs. 0.95 ± 0.09) but was similar at 15 and 60 minutes. At the end of recovery, RER for VIE and MIE were 0.89 ± 0.08 and 0.95 ± 0.09, respectively (p = 0.08). FatOx at the end of recovery was significantly greater in VIE (0.05 ± 0.04 g·min-1) than MIE (0.01 ± 0.03 g·min-1). CONCLUSION: Although, NetVO2 and EE were similar during recovery, VIE appears to alter fuel utilization patterns during recovery towards a lower RER and greater fat oxidation.