Evolution of fat oxidation during exercise in obese pubertal boys: clinical implications

In this study, we examined fat oxidation rates during exercise in obese pubescent boys. Three groups of pubescent boys (16 pre-pubescent, Tanner's stage I; 16 pubescent, Tanner's stage III; and 14 post-pubescent, Tanner's stage V) performed a graded test on a leg cycle ergometer. The first step of the test was fixed at 30 W and power was gradually increased by 20 W every 3.5 min. Oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) were determined as the means of measurements during the last 30 s of each step, which allowed us to calculate fat oxidation rates versus exercise intensity. Between 20 and 50% of peak oxygen consumption (VO(2peak)), fat oxidation rate in relative values (mg . min(-1) . kg FFM(-1)) decreased continuously with pubertal development. In the same way, the maximum rate of fat oxidation occurred at a lower percentage of VO(2peak) (pre-pubescent: 49.47 +/- 1.62%; pubescent: 47.43 +/- 1.26%; post-pubescent: 45.00 +/- 0.97%). Our results confirm that puberty is responsible for a decrease in fat free mass capacities to use fat during exercise. The results suggest that post-pubescent obese boys need to practise physical activity at a lower intensity than pre-pubescent boys to enhance lipolysis and diminish adipose tissue and the consequences of obesity.