MEASUREMENT AND INTERPRETATION ISSUES IN LABORATORY AND FIELD STUDIESOF ENERGY-EXPENDITURE

The methods for measuring energy expenditure in the laboratory and the field are described and critically appraised and the criteria for rel iable and valid measurements identified. Variation and adaptation in t he energy costs of activities and the total daily energy expenditure a re considered in the context of discriminating between what is variati on and adaptation and what is honest error. This involves issues of co mparative energetics and standardization and oxygen uptake kinetics, w hich are frequently neglected or ignored. The energetics of physical w ork, where many of the problems arise, are examined. It is technically feasible to measure energy expenditure with high accuracy, but the me thods required, calorimeter rooms and doubly labelled water, are not w idely available or applicable. The field methods, the factorial method of diary record of activities and their energy costs, and the heart r ate methods are of acceptable accuracy for groups but less so for indi viduals. When using energy costs from the literature, as has been comm on in human biology, several problems arise. The sample sizes are smal l and of unknown provenance, and there is no information on variabilit y or on whether the values are based on continuous or intermittent wor k. The problem of how to allow for differences in size and composition has been tackled with convenience rather than concepts. It is recomme nded that isometric scaling, using kcal/kg, be avoided and allometric scaling by, e.g., analysis of covariance, be used to remove the effect s of size and composition. In investigations of variation and adaptati on in the efficiency of work, the effects of oxygen uptake kinetics an d of anaerobic metabolism must be considered. (C) 1996 Wiley-Liss, Inc .