Discussion (summarized by B. Schürch)

Durnin's initial impression was that the estimates in Torun's Tables of energy expenditure in moderate and heavy activity might be too low. He would have expected that walking on a level surface would cost more than 3 kcal/min. The highest values for heavy activities to be found in Torun's Tables are between 30 and 40% of physical work capacity (VO₂ max). Adults would occasionally expend more energy than that, and the same could be expected in children.

An important issue in this connection is, of course, if occasional pauses are included in the estimates or not. The sources from which Torun took his figures unfortunately do not always clearly indicate whether this is the case or not.

If energy cost data are used in conjunction with results of time-motion studies to make estimates of 24-hour energy expenditure it would be interesting to know if errors are more likely to be greater in energy cost or time-allocation estimates. Torun believes that both kinds of errors can be considerable, but probably more so in time-allocation data. In a time-motion study, McGregor and her colleagues observed and recorded the activity of 12- to 24-month-old children, first once every 10 minutes, then once every minute. The latter procedure made the children appear less active than the former one. Shetty argues that using BMR equations and BMR factors tends to result in overestimates of energy expenditure in the generally lighter adults of developing countries. The same as yet unexplained phenomenon might lead to overestimates of energy expenditures in children living in tropical countries.

Torun's Tables still contain many gaps and the question is raised, as to whether one could not fill them by simulating these activities in a calorimetric chamber and measuring the corresponding energy expenditure. Torun believes that energy expenditure for simulated and real-life activities would differ too much and that only data collected in free-living individuals should be used to predict energy expenditure in real life. Even if one collects energy expenditure data for free-living individuals, biases cannot be completely excluded. Torun and his colleagues usually eliminated data collected during the first 4 to 8 weeks to reduce the Hawthorne effect (which stipulates that individuals under observation act differently from individuals who are not under observation).