Obesity is considered a pandemic [1]. According to the World Health Organization (WHO), in 2016 more than 1900 million adults over 18 years old were overweight, of which 650 million were obese [2]. Besides, obesity and overweight determine a high risk of chronic non-communicable diseases such as type-2 diabetes mellitus, hypertension, cardiovascular disease, and some types of cancers [3], [4].

The Chilean National Health Survey 2016–2017 [5] showed that 74.2% of Chilean population has a BMI ≥ 25. These numbers have induced the development of many initiatives to stop the progression of obesity, due to the high burden of the illness and its comorbidities. According to the WHO, the treatment of obesity should be focused on managing risk factors and long-term weight maintenance, since a decrease of 5–10% body weight has a significant impact on associated diseases [3].

Being physically active is considered a protective factor in obese patients independently of BMI [6]. The American College of Sports Medicine (ACSM) determined that the recommendation for this population at risk is aerobic exercise from moderate to high intensity (40–60% of maximum oxygen consumption), with a duration of at least 20 minutes for five days a week [7]. Moreover, evidence suggests that mild to moderate exercise increases the use of free fatty acids as an energy alternative to carbohydrates [8], [9].

Various exercise referral schemes have been planned for overweight and obese individuals to achieve maximum fat oxidation. Within these programs, bouts of aerobic exercise alternate with periods of rest have been widely studied [10], [11], [12], [13], [14], [15]. Stich et al. [10] and Goto et al. [11], [12] observed a higher rate of fatty acid oxidation in subjects who went through exercise at intervals compared to those who performed it continuously. According to other similar studies [13], [14], [15], there is evidence that bouts of aerobic exercise are more efficient than continuous exercise with equivalent intensity and duration. However, it is necessary to determine the design of a protocol that could allow the optimization of fat oxidation and the applicability in general population.

Therefore, this study aims to compare three different protocols of interval exercise performed at constant, increasing and decreasing intensity respectively: in a apparently healthy, sedentary population of individuals with elevated BMI. Our hypothesis suggests that bouts of exercise of decreasing intensity is the most effective protocol over fat oxidation compared to the other protocols, with equal duration and average intensity.