Effect of Short-term High-intensity Interval and Fatmax Training on Aerobic and Metabolic Fitness in Obese Subjects

Obesity is commonly associated with insulin resistance and hyperinsulinemia, which seem to be linked with an impaired ability to oxidize lipids, particularly in class III obese individuals [Body Mass Index (BMI): > 40 kg*m-2] (1). Exercise training is an effective strategy to improve insulin sensitivity and to reduce the risk of type 2 diabetes (2). It has been suggested that 8 (3) or 10 wk (4) of an individualized moderate exercise training program at intensity (Fatmax) that elicits maximal fat oxidation (MFO) may significantly increase the fat oxidation rates (FORs) during exercise; it may also increase the muscle oxidative capacity in overweight and class I obese men. The effects of an individualized Fatmax training program of a shorter duration have never been investigated.

High-intensity interval training (Wingate-based HIIT) has been shown to induce similar adaptations as traditional training at a moderate intensity following 6 wk of training in healthy adults despite the lower training volume (5). This suggests that HIIT may be a time-efficient alternative (6). Recently, HIIT was also reported to rapidly induce adaptations that are linked to improved health-related outcomes in sedentary and overweight/obese individuals (7, 8).

This study aimed to compare the effects of two different 2-wk-long training modalities [continuous at the intensity eliciting the maximal fat oxidation (Fatmax) versus adapted high intensity interval training (HIIT)] on aerobic and metabolic fitness of class II and III obese men. It was hypothesized that, because of the nature of HIIT in the stimulation of rapid changes, aerobic fitness, fat oxidation rates during exercise and insulin sensitivity would be improved to a greater extent when trained with adapted HIIT compared to Fatmax training.

A group of twenty obese men (BMI≥35 kg*m-2) will be assigned to Fatmax group or to adapted HIIT group. Both groups will perform 8 cycling-sessions matched for mechanical work spread over 14 days [40-50 min continuous exercise at ~60-70% of the maximal heart rate (Fatmax) or 10x60-s cycling intervals a ~90% maximal heart rate interspersed with 60-s recovery (HIIT)]. Aerobic fitness and fat oxidation rates (FORs) during exercise will be assessed prior to and following the training with a maximal incremental test. Blood samples will also be drawn to determine hormones and plasma metabolites levels. Insulin sensitivity was assessed by the homeostasis model assessment of insulin resistance (HOMA).

The experimental design will consist of the following: 1) maximal ramp incremental test, to determine peak power output of each subject. 2) pre training test with blood samples, maximal incremental test (Incr) to determine the whole-body fat oxidation kinetics and Fatmax in the first phase (IncrP1) and the maximal parameters in the second phase (IncrP2) of the test. 3) 2-wk training intervention, Fatmax or HIIT and 4) post-training test, control maximal incremental test with blood samples.