At this time, 24h energy expenditure is rarely assessed under free-living conditions for specific individuals because of the lack of cheap and accurate software/materials to record the energy expenditure. Some affordable and convenient tools (Polar heart rate monitor, Actiheart, SenseWear Armband) are available on the market but the predictive equations comprised into the software provided with these tools generally miscalculate the energy expenditure (by about +/-10%). Because of this deficiency, the investigators have a poor knowledge of the modification of the energy expended during daily life activities and over 24h in subjects belonging to groups of various ages and physiological states. The investigators hypothesise that it could be possible to improve the energy expenditure prediction.