Effects of Altering the Sequence of a Combined Aerobic and Resistance Exercise Session on Energy Expenditure and Metabolism
Bedbrook, Megan Joy
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Despite the known benefits of performing aerobic and resistance exercise independently, the metabolic effects of performing aerobic and resistance exercise in succession, remain unclear. Several studies suggest that the alteration of exercise sequence may influence carbohydrate and lipid oxidation and energy expenditure during exercise and in recovery. High intensity resistance exercise performed prior to a bout of aerobic exercise has been shown to augment fat oxidation during the subsequent bout of aerobic exercise. Changes in hormone and metabolite concentrations from prior resistance exercise could potentially influence substrate selection and energy expenditure in a subsequent bout of aerobic exercise. However, an exercise session whereby aerobic exercise is followed by a bout of resistance exercise has yet to be evaluated to determine the metabolic effects (specifically, the differences in substrate selection for energy provision) when exercise sequence is altered. It was hypothesized that when resistance exercise was performed prior to a bout of aerobic exercise, sympathetic nervous system activity would be elevated, leading to an increase in non-esterified fatty acid (NEFA) and glycerol concentrations and resultant increase in lipid oxidation during the aerobic portion of the exercise compared to the opposite sequence. It was also hypothesized that during recovery there would be an increased reliance on fat oxidation for energy provision with a resistance-aerobic exercise sequence compared to an aerobic-resistance exercise sequence. Additionally, the differences in metabolite concentrations and respiratory parameters between two identical bouts of aerobic exercise performed on separate days (~1 week apart) were measured and it was hypothesized that day-to-day variability would be non-significant (p>0.05). Plasma glucose, lactate, NEFA, glycerol, insulin, C-peptide, glucagon, epinephrine and norepinephrine concentrations in addition to oxygen consumption (VO2) and respiratory exchange ratio (RER) were measured in nine healthy, recreationally active males that participated in 3 different, randomized exercise trials (Trial A: aerobic exercise; Trial AR: aerobic exercise followed by a bout of resistance exercise; Trial RA: resistance exercise followed by an aerobic exercise bout). The aerobic exercise bout was performed at 60% VO2 max for 30 min while the resistance exercise bout consisted of 5 exercises (overhead squat, chest press, triceps extension, shoulder press, and dead-lift) performed for 3 sets of 8 repetitions at 70% 1-RM. Contrary to the primary hypothesis, NEFA concentrations and lipid oxidation rates were similar for the aerobic exercise bout of both the AR and RA trials. During recovery, lipid oxidation was elevated immediately post-exercise in the RA trial compared to the AR trial, however there were no differences between trials by 15 min post-exercise. Furthermore, only epinephrine, and not norepinephrine, concentrations were significantly higher after aerobic exercise in the RA trial compared to the AR trial. VO2 and energy expenditure values were similar for the duration of the 30 min recovery. These results suggest that while exercise sequence may influence carbohydrate and lipid oxidation immediately post exercise, substrate selection and utilization are similar during aerobic exercise bouts irrespective of the sequence in which aerobic and resistance exercise are performed. Thus, when resistance exercise is performed prior to aerobic exercise, compared to the opposite sequence, overall energy provision is not altered at the volume and intensity of exercise performed in this study.