Introduction: The primary aim of the current study was to determine the effect of two doses of chronic high-intensity interval training (HIT) on changes in maximal fat oxidation (MFO) and body composition.
Methods: Sedentary women (N = 23, age and V˙O2max = 24.2 ± 6.2 yr and 30.3 ± 5.2 mL·kg−1·min−1, respectively) completed either high (HI) (80%–90% maximal workload) or moderate (MOD) intensity (60%–80% maximal workload) HIT on a cycle ergometer 3 d·wk−1 for 12 wk consisting of 6–10 sixty-second bouts interspersed with active recovery. Seven women of similar age and fitness level served as controls. Every 3 wk, substrate oxidation was assessed during progressive exercise via indirect calorimetry to determine MFO and minimum fat oxidation, and body composition was assessed every 6 wk. Repeated-measures ANOVA was used to examine changes in substrate oxidation in response to training, with training group used as a between-subjects variable.
Results: Results revealed improved MFO (P = 0.04, 19%–25%) and minimum fat oxidation (P = 0.001, 22–24 W) in response to HIT, yet the magnitude of improvement was similar (P > 0.05) between training paradigms. No change (P > 0.05) in body weight, percent body fat, or waist–hip circumference was revealed with training.
Conclusion: These data suggest that 12 wk of either moderate or more strenuous interval training similarly enhance fat oxidation in sedentary women but do not alter body weight or body composition.