Measurement must be done on an empty stomach after 8 hours sleep. During the measurement we use mask, recumbent position is required as well as complete mental and physical relaxation. At this stage ( using ergospirometry ) the amount of energy, which is needed to perform all physical functions during times of complete rest and fasting is measured. BMR is helpfull for dietitians to have an idea of the total amount of food or calorie required to maintain body weight.