Changes in body composition and daily energy expenditure induced in rats during eight weeks of daily swim training.

The body weight, body composition, and daily (post-exercise) energy expenditure of five groups of male rats were examined following 1, 2, 4, 6 or 8 weeks of daily (1 h) swim training. Rats that swam daily weighed less than sedentary controls and had smaller adipose and lean tissue masses. The size of these body weight and composition changes grew as daily training progressed. Relative to sedentary rats, the 24 h (post-exercise) expenditure of swim-trained rats, expressed either per BW0.75kg or per g of body protein, was significantly higher after two weeks of daily training. This training-induced elevation in daily (post-exercise) expenditure likewise grew larger as training continued. After eight weeks, rats that swam, although now maintaining significantly smaller lean and adipose masses, expended more calories daily (post-exercise) than sedentary rats (42.2 vs. 39.2 kcal/day respectively). Thus, though exercise-induced elevations in expenditure have been associated with an increased lean tissue mass, other factors are apparently responsible for the progressive elevation (from sedentary levels) of 24 h expenditure found here with extended daily swim training.

Amount of exercise per day and weeks of training: effects on body weight and daily energy expenditure.

The effects of 16 wk of 1 or 3 h of daily swim-training on the body weight and 24-h postexercise energy expenditure of adult male Sprague-Dawley rats were examined. Daily energy expenditure (kcal.d-1.kg-0.75) of sedentary rats displayed the usual age-associated decline in daily energy expenditure (kcal.d-1.kg-0.75) over this 16-wk period. Daily swimming forestalled this decline, leading to differences in daily energy expenditure between exercised and sedentary rats, which grew progressively larger. One and 3 h of daily swimming led to similar declines in weight, but 3 h of daily swimming elevated daily (postexercise) expenditure after fewer weeks of training and to a greater extent than did 1 h of daily swimming. Exercise-induced elevations in daily (nonexercise) expenditure thus appear to be a joint function of how long the daily exercise program has been in effect and the amount of daily exercise.

Exercise intensity does not affect the composition of diet- and exercise-induced body mass loss.

The effect of caloric restriction (1200 kcal/d intake) in combination with high (High) (80-90% of peak VO2) or low (Low) (40-50% of peak VO2) exercise work rates on the composition of lost body mass was determined in 27 obese women (percent fat, 36.7 +/- 4.2%; mean +/- SD). All subjects trained 3 d/wk for 8 wk, with the High (n = 14) and Low (n = 13) groups exercising for 25 and 50 min/d, respectively. After posttesting there were no differences between the groups with respect to pre- to posttest changes (mean of combined groups) in body mass (-7%), fat-free mass (-10%), fat mass (-16%), percent fat (-10%), and sum of five skinfold-thickness measurements (-16%). This study suggests that with regard to conservation of fat-free mass, the selection of an exercise intensity for a diet and exercise regimen may be left to the preference of the clinician and/or dieter.

Resting oxygen consumption in over- and underfed rats with lateral hypothalamic lesions.

Rats maintaining stable, reduced body weights following lateral hypothalamic (LH) lesions were given either ad lib amounts of a palatable liquid diet or restricted amounts of a hydrated chow diet. The palatable diet produced weight gains while the diet restriction led to weight reductions in both LH- and sham-lesioned rats. Body composition analysis indicated that these changes in body mass were accounted for largely by changes in carcass fat. Resting oxygen consumption (expressed relative to body weight raised to the 3/4 power) was altered by both dietary regimens. Resting oxygen consumption in sham-lesioned rats increased by 5% following overfeeding and decreased by 13% following food restriction. LH-lesioned rats made similar responses to these dietary challenges. Overfed LH-lesioned rats increased their rate of resting oxygen consumption by 11%. Underfed LH-lesioned rats decreased oxygen consumption by 11%. These findings provide further evidence that rats with LH lesions defend a reduced level of body weight. The changes in energy expenditure that mitigate weight change in sham-lesioned animals are also present in LH-lesioned rats. In the latter, however, these adjustments serve to stabilize body weight at a lower level.