Acute Metabolic Responses To Isoenergetic HIIT Cycling Vs. Running Sessions In Overweight And Obese Men

INTRODUCTION: High-Intensity Interval Training (HIIT) is a promising strategy to reduce fat mass in individuals with obesity. The choice of exercise modality, including muscle groups engaged and muscle contraction type, could influence oxygen consumption (VO2), substrate utilization, and energy balance in the hours post-HIIT session. PURPOSE: The aim of this study was to compare the acute effects of isoenergetic HIIT running (HIIT-RUN) and cycling (HIIT-BIKE) sessions on post-exercise VO2, fat oxidation, and 24-hour energy balance. METHODS: Eight fasted men (50 ± 13 years; BMI: 28.8 ± 1.9 kg.m-2) completed two isoenergetic HIIT sessions (HIIT-RUN and HIIT-BIKE) in a counterbalanced randomized order. Sessions included a 5-min warm-up followed by 9 to 12 intervals of 45 s at 85% of Heart Rate Reserve (HRR) and 90s at 40% of HRR. VO2 and VCO2 were measured at rest, during exercise, and 2 h post-exercise. Carbohydrate and fat oxidation (g and %) were calculated at rest and during recovery. Enjoyment (PAES), perceived exertion (RPE) and appetite (VAS) were recorded during the session. Energy intake (EI) and expenditure (EE) were assessed with questionnaires in the following 24 h. RESULTS: Both sessions displayed similar EE (kcal), but HIIT-BIKE induced a greater mean respiratory exchange ratio value (p < 0.01). No significant modality effect or time x modality interaction was observed for VO2 and EE in the 2 h post-exercise. Overall, fat oxidation (g and %) was significantly higher during the recovery period compared to the resting phase (p < 0.05), with a greater amount of oxidized fat observed post-running (p < 0.05). Despite similar PAES scores at the end of both sessions, perceived exertion was higher after cycling. Appetite (VAS) and 24 h EI and EE adaptations were similar after both sessions. CONCLUSIONS: In men with overweight or obesity, the two acute isoenergetic HIIT sessions (cycling and running) elicited similar VO2 and EE in the 2 h recovery period promoting fat oxidization. In the context of fat mass loss, HIIT running could more effective in enhancing body composition.