 The overall goal is to determine whether any energy expenditure compensation in response to 16 weeks of aerobic exercise at a higher-dose is greater compared to a lower-dose intervention in older women, and to begin to investigate underlying physiological mechanisms that influence energy expenditure changes in older women. Changes in all components of energy expenditure, as well as concentrations of plasma leptin and serum free T3, in response to the two different exercise programs 14 and 8 kcalkg body weight weekly, 60-65 VO2max, 4 dayswk will be compared in older, non-obese women 60-75 yrs, BMI18-30 kgm2. 