WILTERDINK, E. J., D. L. BALLOR, and R. E. KEESEY. Amount of exercise per day and weeks of training: effects on body weight and daily energy expenditure. Med. Sci. Sports Exerc., Vol. 24, No. 3, pp. 396–400, 1992. 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.