Energy Expenditure And Fat Utilization During And After Interval Versus Continuous Self-paced Exercise Bouts

Abstract

PURPOSE: Exercise is often performed to achieve high energy expenditure (EE) and fat oxidation (FO). The purpose of the study was to compare exercise EE, early recovery EE (REE), and total FO during self-paced "hard interval" vs "talking intensity" continuous exercise bouts typical of fitness industry exercise prescriptions. METHODS: After preliminary testing, 9 regularly active males (age 28 ± 6 yr, VO2max 55 ± 5 ml·min-1·kg-1) performed a self-paced high intensity interval session (INT) consisting of six, 4 min work bouts interspersed by 2 min recovery periods (34 min total exercise time) with continuous gas exchange measurement during the 34 min exercise session and for 30 min post exercise. Responses were compared with those measured during a "talking intensity" exercise bout of identical total duration (SS). The two bouts were performed in randomized order. EE, REE, and FO were estimated from continuous measurements of respiratory gas exchange. Fat oxidation calculations are considered minimum estimates due to presumed contamination of CO2 production with CO2 release due to H+buffering. RESULTS: The INT session elicited higher average heart rate (171 ± 14 vs 154 ± 15, p<0.001), blood lactate concentration (6.5 ± 2.8 vs 2.1 ± 1.1 mmol·L-1, p<0.001), and RPE (17 ± 1 vs 12 ± 1, p<0.001) than the SS session. EE during INT was ∼12% higher (555 ± 75 vs 495 ± 68 kcal, p<0.01) and 30min REE was 23% higher (89 ± 15 vs 72 ± 9 kcal, p<0.01). FO during 34 min exercise tended to be higher in SS (13.0 ± 5.3 vs 9.4 ± 4.5 g, p = 0.12). FO during the first 30 min post-exercise was higher after INT (4.5± 1.4 vs 2.5 ± 1.3 g. p = 0.02). Total FO (34 min exercise+30 min recovery) was similar in the interval based and continuous exercise sessions (13.0 ± 3.7 vs 15.5 ± 6.4 g, p= 0.56). CONCLUSIONS: In this study, we have attempted to simulate two exercise prescriptions typical of the time constraints and intensity goals of "1 hour fitness classes". Our results suggest that for the same time investment, self-paced interval training results in significantly greater total energy expenditure and similar total fat oxidation than continuous exercise performed at "talking intensity."