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.