Abstract: A method and apparatus is disclosed for determining the energy requirements of premature newborns. The method includes identifying a series of groups of newborns in which the age and weight of each newborn within each group are within defined ranges. A characteristic mathematical relationship is generated for each group and relates the mean heart rate to the mean energy expenditure over the group. The mean heart rate of a subject newborn, the energy expenditure which is to be determined is measured and applied to the mathematical relationship appropriate to the group into which the subject falls, so as to determine the mean energy expenditure appropriate to that mean heart rate, said expenditure indicating the energy requirement of the subject.