REGULAR EXERCISE AND THE AGE-RELATED DECLINE IN RESTING METABOLIC-RATE IN WOMEN

A low resting metabolic rate (RMR) is a risk factor for future weight gain. We tested the hypothesis that the age-related decline in RMR in sedentary women is not observed in women who exercise regularly. Sixty -five healthy, weight-stable women, aged 21-35 or 50-72 yr, were studi ed: 12 premenopausal and 15 postmenopausal sedentary women, 13 premeno pausal and 15 postmenopausal distance runners, and 10 endurance-traine d postmenopausal swimmers. RMR was measured by indirect calorimetry (v entilated hood system) after an overnight fast, and values were adjust ed for fat mass and fat-free mass (RMRadj). The RMRadj was similar to 10% lower in the postmenopausal vs. premenopausal sedentary women (52 +/- 2 vs. 57 +/- 2 Cal/h; P < 0.002). In contrast; RMRadj was not sign ificantly different in the premenopausal (59 +/- 2 Cal/h) and postmeno pausal (57 +/- 1 Cal/h) distance runners. The postmenopausal swimmers had a RMRadj (57 +/- 2 Cal/h) identical to that of the postmenopausal runners, suggesting a generalized influence of the endurance exercise- trained state in postmenopausal women. Group differences in RMRadj wer e not associated with differences in total energy intake or compositio n or with plasma concentrations of norepinephrine, T-3, or T-4. Howeve r, maximal oxygen consumption (aerobic fitness) accounted for 35% of t he individual variance in RMRadj in the overall population (r = 0.59; P < 0.001). Our results are consistent with the concept that the age-r elated decline in RMR in sedentary women is not observed in women who regularly perform endurance exercise. The elevated level of RMR observ ed in middle-aged and older exercising women may play a role in their lower levels of body weight and fatness compared to those in sedentary women.