Effects of 3-month high-intensity interval training vs. moderate endurance training and 4-month follow-up on fat metabolism, cardiorespiratory function and mitochondrial respiration in obese adults

Purpose: The purpose of this study was to investigate, in obese adults, changes in body composition, physical capacities, fat oxidation and ex vivo mitochondrial respiration induced by a 3-month either moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT); afterwards, the patients were followed for four months. Methods: Thirty-two patients (mean age 39 years; mean body mass index [BMI] 36 kg∙m−2) participated in this study attending ~ 34 sessions of training. At baseline (PRE), at the end of the program (POST) and after follow-up, body composition, peak O2 uptake (V′O2peak) and fat oxidation rate were measured. Vastus lateralis biopsies for the evaluation of mitochondrial respiration were performed only at PRE and POST. Results: At POST, body mass (BM) and fat mass (FM) decreased (− 6 and − 14%, respectively, P < 0.05) in MICT and HIIT; V′O2peak increased in both groups (+ 6 and + 16%, respectively, P < 0.05). Maximal fat oxidation rate increased only after HIIT (P < 0.001). Maximal ADP-stimulated mitochondrial respiration normalized by citrate synthase increased (P < 0.05) by 67% and 36% in MICT and HIIT, respectively, without significant difference. After follow-up, BM and FM were still lower (− 4 and − 20%, respectively, P < 0.050) compared with baseline in both groups. Only after HIIT, V′O2peak (+ 8%) and maximal fat oxidation rate were still higher (P < 0.05). Conclusions: HIIT was more effective in improving and maintaining V’O2peak and fat oxidation. These results may be relevant for an appropriate prescription of training programs designed to optimize aerobic fitness in obese subjects.