EXERCISE INTENSITY DOES NOT AFFECT DEPRESSION OF RESTING METABOLIC-RATE DURING SEVERE DIET RESTRICTION IN MALE SPRAGUE-DAWLEY RATS

This study examined the effects of high and low intensity exercise on the resting metabolic rate during severe dietary restriction. We hypot hesized that exercise would attenuate and/or offset the decline in res ting metabolic rate during energy-deficit conditions. Thirty-two male 90-d-old Sprague-Dawley rats were divided into four groups: control, d iet restriction only, diet restriction plus high intensity exercise, a nd diet restriction plus low intensity exercise. The body weights of t he diet-restricted groups were rapidly reduced over 5 wk until rats in these three groups weighed 64% of control weight, and this difference in body weight was maintained for the last 5 wk of the study. The hig h and low intensity exercise groups ran 5 d/wk at 75 and 37.5%, respec tively, of maximal running speed for 45 and 90 min/d, respectively. Re sting metabolic rate (23-h oxygen uptake) was measured during wk 2, 4, 6, 8 and 10. Resting metabolic rate for the three diet-restricted gro ups was significantly lower (25-37%) than for the controls for all mea surements. Exercise training had no effect on the diet-induced depress ion of resting metabolic rate, with the diet-restricted groups differi ng among each other by <2% during the measurement periods. During seve re diet-restriction, exercise-induced elevations of resting metabolic rate seem to be greatly reduced or eliminated. This absence of an exer cise effect on resting metabolic rate persisted through 5 wk of reduce d body weight maintenance. We conclude that during severe diet restric tion, exercise offers no ''protective'' or enhancing effect on resting metabolic rate.