Am J Clin Nuir l992;55:777-82. Printed in USA. © 1992 American Society for Clinical Nutrition 777 Total energy expenditure and spontaneous activity in relation to training in obese boys1’2 Ellen E Blaak, Klaas R Westerterp, Oded Bar-Or, Loek JM Wouters, and Wim HM Saris ABSTRACT Obese boys [n = 10, aged 10- 11 y, average percent body fat (%BF) 32.4] were given a regimented training program (4 wk, 5 1-h sessions, 45 mm cycling/wk at 50-60% of predetermined VO2max) to investigate whether they modify their energy expenditure by reducing or augmenting their spontaneous physical activities. No change was observed in mean weight (52.7 vs 52.9 kg), %BF based on 2H- and ‘80-dilution and densitometry (32.4 vs 31.7), sleeping metabolic rate (5.83 vs 5.68 MJ/24 h), and spontaneous activity by heart rate recording (percent time oflight intensity: 85.3 vs 83.6; medium: 1 1.2 vs 12.4; and heavy: 3.5 vs 3.9) and activity questionnaires (861 vs 821 mm physical activity/wk). There was a 12% increase in average daily metabolic rate by doubly labeled water, half ofwhich can be explained by the energy cost oftraining and the rest by an increase in energy expenditure outside the training hour. In conclusion, training leads to an appreciable augmentation in the overall energy cx- penditure ofobese children, even with a lack ofchange in spon- taneous physical activity. Am J Clin Nutr l992;55:777-82. KEY WORDS Energy expenditure, spontaneous activity, training, children, doubly labeled water, obesity Introduction Recently, the interest in the potential of adding exercise to the treatment of obesity has increased. Exercise is by far the most flexible component of energy expenditure in the energy- balance equation. By increasing exercise a higher energy expen- diture can be achieved and this might result, when intake does not change, in a higher weight loss. However, conflicting results have been found about the efficacy ofadding exercise to diet in weight-loss programs. Although a higher weight loss as a result ofincorporating exercise has been reported (1), other studies (2, 3) found no change. This lack of conclusive results might be partially explained by a concomitant change ofother components of the energy-balance equation. A factor that might contribute to the controversial results is a change in food intake as a result of exercise training. Early studies in rats indicated that when a highly sedentary animal increases its level of activity, appetite may decrease with mild levels ofactivity but increase with mod- crate levels (4). Support for such a phenomenon in humans is weak. Whatever the effect in humans may be, it appears that very small changes in energy intake accompany exercise training (5). Another factor that might explain the sometimes disappointing results ofadding training to weight-loss programs was suggested by Epstein and Wing (6). Subjects may, as result of training, reduce their normal daily activities or nonexercise activities to compensate for the energy deficit. Such a reduction in sponta- neous daily activities might compensate for the additional pre- scribed exercise, thus resulting in an unchanged total energy expenditure from that found before training. Two studies in adults investigated this possibility. In lean and obese women no indications ofcompensation in normal daily activities were de- tected (7, 8), whereas in lean males a training regimen stimulated spontaneous physical activity during the nontraining hours of the day (8). So far, no studies are available that report on the effect oftraining on the spontaneous activity in obese children. The response to exercise isn’t necessarily equal in children and in adults mostly because children have a more flexible time schedule (more spare time) and therefore are more likely to modify their spontaneous activity. To better understand the ef- ficacy of training in the management of childhood obesity, one needs to know the net increment ofenergy expenditure. There- fore, the present study focuses on the effect of training on total energy expenditure and spontaneous activity outside the training hours in obese boys. Subjects and methods Subjects Ten 10-1 1-y-old boys were selected on the basis of their per- centage body fat (between 30 and 40) from a group of overweight boys who had been approached in writing by the Maastricht School Health Service Physician. To exclude health abnormal- ities that would interfere with their resting metabolic rate (RMR) or their ability to sustain a training program, a medical history was taken. Two subjects were asthmatic but were well-controlled by medication and had no limitations in their exercise ability. Informed written consent was obtained from the volunteers and their parents. The study was reviewed and approved by the ethics committee of the university. Physical characteristics ofthe sub- jects are indicated in Table 1. I From the University of Limburg, Maastricht, The Netherlands, and McMaster University, Hamilton, Canada. 2 Address reprint requests to EE Blank, Department ofHuman Biology, University of Limburg, Postbus 616, 6200 MD Maastricht, The Neth- erlands. Received January 22, 1991. Accepted for publication September 1 1, 1991. at Institute of Atmospheric Physics,CAS on July 9, 2011 www.ajcn.org Downloaded from