Isocaloric High-Intensity Interval and Circuit Training Increases Excess Post-Exercise Oxygen Consumption and Lipid Oxidation Compared to Moderate-Intensity Continuous Training

Background: This study compared energy expenditure (EE), substrate metabolism, and excess post-exercise oxygen consumption (EPOC) during moderate-intensity continuous training (MICT), high-intensity interval training (HIIT), and high-intensity circuit training (HICT) isocaloric sessions. Methods: Twelve trained male participants completed isocaloric exercise sessions equalized for EE and average power (AP) across the three modalities. Postexercise EE, carbohydrate and lipid oxidation rates, and EPOC were measured 30 and 60 min after training. Results: Total EE and AP during exercise were similar between the protocols. However, EPOC was significantly higher for HIIT (319.0 ± 88.03 mL) and HICT (329.1 ± 27.79 mL) than for MICT (168.5 ± 21.84 mL), demonstrating greater post-exercise metabolic demand in high-intensity protocols. At 30 min post-exercise, carbohydrate oxidation remained elevated in the HIIT (3.70 ± 1.04 mg/kg/min) and HICT (4.06 ± 1.03 mg/kg/min) groups compared to that in the MICT group (1.42 ± 0.58 mg/kg/min), while lipid oxidation rates were also higher (HIIT: 1.08 ± 0.41; HICT: 1.20 ± 0.24 mg/kg/min; MICT: 0.61 ± 0.20 mg/kg/min). These effects persisted for 60 min, with HIIT and HICT maintaining significantly greater carbohydrate and lipid oxidation than MICT. Correlation analysis indicated a strong relationship between carbohydrate oxidation during exercise and lipid oxidation after 60 min of exercise. Conclusions: High-intensity protocols (HIIT and HICT) promote prolonged postexercise EE, enhance carbohydrate and lipid oxidation, and optimize metabolic recovery, making them effective strategies for maximizing energy utilization beyond the training session.