Long-term exercise training with constant energy intake. 1: Effect on body composition and selected metabolic...

The effects of long-term negative energy balance generated by exercise while maintaining a constant energy intake were studied in five healthy young males (25 +/- 3 years; mean +/- s.d.). After 2 weeks of monitoring to determine habitual energy intake, they were subjected to a 100-day experimental period during which they exercised on a cycle ergometer, 6 days a week, twice a day at 55 per cent of VO2 max. The daily energy deficit was 4.2 MJ for a total of 353 MJ for the duration of the treatment. Body weight decreased from 86.7 to 78.7 kg (P less than 0.001). More than 80 per cent of the weight loss was accounted for by the reductions in fat mass. Fat-free mass did not change significantly. The data suggest that subcutaneous fat was lost about evenly from the trunk and from the limbs as estimated from skinfolds. Cardiorespiratory and metabolic responses to submaximal work loads indicate that the low intensity exercise regimen was capable of inducing some of the known adaptations of exercise training such as a decrease in plasma insulin and norepinephrine concentrations during exercise, reductions in heart rate, pulmonary ventilation and blood lactate concentration at a given exercise intensity, and an increase in skeletal muscle oxidative capacity. The energy cost of sitting and standing was not decreased in spite of the loss in body mass. However, the energy cost of submaximal cycling and walking exercises was reduced considerably. These results clearly demonstrate that it is quite possible to lose fat while preserving fat-free mass through regular prolonged exercise of moderate intensity if energy intake is kept constant at baseline level. They also emphasize the importance of the individual differences in response to negative energy balance.