Physical Activity and Basal Metabolic Rate in Postmenopausal Women

The primary purpose of this study is to expand research on the effects of physical activity on basal metabolic rate (BMR) in healthy postmenopausal women, and to further compare the effects of long-term habitual exercise to the results of a shorter-term (16 weeks) training program. The investigators will measure BMR by indirect calorimetry and normalize it across subjects for body size (fat free mass) and level of aerobic fitness (VO2MAX). Two groups will be compared: an intervention group (no previous participation in regular exercise, newly enrolled in this study's 16 week training program), and a long-term athlete group (have engaged in at least 5 hours of exercise per week for the past 10 years or longer). A secondary aim is to generate an equation for the prediction of BMR from fat free mass in physically active postmenopausal women, to be applied to hypotheses in biological anthropology. The investigators expect to find at baseline that, controlling for fat free mass and VO2MAX, the long-term group will have significantly higher BMR than the intervention group. At 16 weeks the investigators expect no change in BMR for the long-term group, while BMR will have increased in the intervention group. At the same time, the investigators expect to find that after completing the training regimen, the intervention group will have BMR similar to that of the long-term athletes.