 20 adolescent boys 10 obese and 10 leans and 20 men 10 obese and 10 lean will complete a sub-maximal test on a ergo cycle to draw their linear relationship between VO2 and Fc. Then they will enter a metabolic chamber three times, for 24 hours each. A first session will be considered as sedentary, and volunteers will remain inactive. During the second and third session, they will have to complete a cycling test generating an energy expenditure of 400 Kcal, once at low intensity 40VO2max and once at high intensity 70 VO2max. Those three sessions will be realized in a randomized order with an interval of at least 7 days and urinary collection over the 24hours will be done during all the sessions. At the beginning of the protocol, blood samples will be taken, body composition assessed by DXA and adiposity location evaluated by MNR. 