Abstract

THE ARRANGEMENT OF SHORT EXERCISE INTERVALS OF DIFFERENT INTENSITIES INFLUENCES THE AMOUNT OF FAT OXIDATION IN SEDENTARY OVERWEIGHT ADULT MEN von Oetinger, A.1,2, Cancino, J.3, Villanueva, B.4, Urzúa, R.2,5, Muñoz, M.5, Villanueva, S.4 1: Universidad Nacional Andrés Bello (Santiago, Chile), 2: Universidad Diego Portales (Santiago, Chile), 3: Universidad Mayor (Santiago, Chile), 4: Universidad de Chile (Santiago, Chile), 5: Hospital del Trabajador (Santiago, Chile) Introduction Since sedentarism is an important cause of obesity, it is relevant to design simple exercise protocols that maximize fat oxidation. The aim of this study was to analyse whether the sequence in which three short periods of exercise of different intensities are arranged influences the oxidation of fat in sedentary overweight adult men. Methods Peak aerobic power (pAP) was determined for ten sedentary male subjects, 30 to 39 years old (33.9 ± 0.9 years), with an elevated body mass index (30.1 ± 0.8 kg/m2). Subsequently, they completed three sessions of equivalent interval-exercise protocols on different days. Each session consisted of three 15 min-exercise periods separated by 5 min of rest between them. In one of these protocols (“constant intensity protocol”, C) all three exercise periods were executed at 55% of pAP. In the other two protocols, the exercise periods were done at 40%, 55% and 70% of pAP, in that sequence (“increasing intensity protocol”, I) or in inverse order (“decreasing intensity protocol”, D). Indirect calorimetry measurements showed that the exercise protocols produced the same caloric expenditure (5.9 ± 0.2 kcal/kg for C, 6.0 ± 0.2 kcal/kg for I and 6.1 ± 0.2 kcal/kg for D; p > 0.01). Results Respiratory exchange ratio data revealed that the proportion of calories contributed by the oxidation of fat (F) and carbohydrate (CH) to the total energy expenditure was significantly different in each exercise protocol (F/CH ratio values: 0.37 ± 0.02 for C, 0.29 ± 0.01 for I and 0.44 ± 0.02 for D; p < 0.01). In addition, the perception of exertion (Borg, 1982) by the subjects was significantly lower in the decreasing intensity protocol (scale of perceived exertion ratings: 14.1 ± 0.4 for C, 16.4 ± 0.7 for I and 12.2 ± 0.3 for D; p < 0.01). Discussion Our results showed that an interval exercise protocol of decreasing intensity was more efficient in fat oxidation and caused a diminished sensation of exhaustion than equivalent (isocaloric) exercise protocols of constant or increasing intensities. Based on the inhibitory effect of glycogen content on muscle fat oxidation (Philp et al., 2012), it is hypothesized that the highest intensity exercise interval at the beginning of the protocol could deplete muscular glycogen, allowing greater fat utilization during the following intervals. References Borg GA. (1982). Med Sci Sports Exerc, 14(5), 377-381. Philp A, Hargreaves M, Baar K. (2012). Am J Physiol Endocrinol Metab, 302(11), E1343-E1351.