Measurement and interpretation issues in laboratory and field studies of energy expenditure.

The methods for measuring energy expenditure in the laboratory and the field are described and critically appraised and the criteria for reliable and valid measurements identified. Variation and adaptation in the energy costs of activities and the total daily energy expenditure are considered in the context of discriminating between what is variation and adaptation and what is honest error. This involves issues of comparative energetics and standardization and oxygen uptake kinetics, which are frequently neglected or ignored. The energetics of physical work, where many of the problems arise, are examined. It is technically feasible to measure energy expenditure with high accuracy, but the methods required, calorimeter rooms and doubly labelled water, are not widely available or applicable. The field methods, the factorial method of diary record of activities and their energy costs, and the heart rate methods are of acceptable accuracy for groups but less so for individuals. When using energy costs from the literature, as has been common in human biology, several problems arise. The sample sizes are small and of unknown provenance, and there is no information on variability or on whether the values are based on continuous or intermittent work. The problem of how to allow for differences in size and composition has been tackled with convenience rather than concepts. It is recommended that isometric scaling, using kcal/kg, be avoided and allometric scaling by, e.g., analysis of covariance, be used to remove the effects of size and composition. In investigations of variation and adaptation in the efficiency of work, the effects of oxygen uptake kinetics and of anaerobic metabolism must be considered. © 1996 Wiley-Liss, Inc.