Intra-individual variability and measurement noise in estimates of energy expenditure by whole body indirect calorimetry.

1. Four men were each studied continuously over 12 d in a whole-body calorimeter. Dietary intake and daily activities were kept constant throughout the study. 2. Day-to-day coefficients of variation in energy expenditure within subjects were found to be 1.97% over 24 h, 5.93% during basal metabolic rate measurement, 2.40% overnight and 3.22% in exercise. 3. The contribution of measurement system noise to the observed variability was analysed and shown to be generally small. The source of this noise was considered. 4. The results reinforce and extend other comparable reports and show that within-subject variability forms a small part of reported observations of between-subject variability.