The project aims at providing a mathematical model (equations) that predicts energy expenditure with an error near to 5%. Two groups of 60 sedentary to athletic normal weight volunteers aged between 18-60 years participate to this study. The first group stay for 26h in calorimetric chambers. During this stay energy expenditure ,heart rate, accelerometry, and other parameters are recorded during various activities. These data will serve to construct the model. The same type of recordings are performed on second group of volunteers in free living conditions. Their energy expenditure is measured overall by doubly labeled water. The data of the second group will serve to validate the model. The error percentage of the model is defined by the ratio of the value of the difference between prediction and reference measure to the reference measure. Concordance between predictions and measures will be evaluated by Bland - Altman plots.