Recent obesity prevalence increases have made obesity prevention a clear and pressing public health issue. The average US. woman gains about 0.5 kg per year, 60 to 80% of which can be assumed to be fat. Overweight women aged 25 to 44 have a higher prevalence of significant weight gains (BMI increases of > 5 kg/m2) than men or older or thinner women. Total and visceral abdominal fat gains are associated with a variety of obesity co-morbidities, including insulin resistance, hypertension, and dyslipidemia. The difficulty in successfully losing weight and maintaining weight loss has resulted in recommendations from several expert panels to advise overweight and mildly obese individuals free of co-morbidities to avoid weight gains rather than to lose weight. Physical activity is observed to decline with age while caloric intake remains stable or declines slightly. There is strong observational evidence that physical activity could prevent or attenuate age associated fat gains. This randomized, controlled behavioral intervention trial will test the hypothesis that regular participation in a twice weekly strength training program over 2 years, can prevent age associated body fat increases (total and visceral abdominal fat) in 80 overweight to mildly obese premenopausal women (BMI 25-35 kg/m2) between the ages of 25 and 44 years, compared to a 'standard care' group (n=80). The overall aim of the study is to prevent body fat gains and to reduce health risks associated with obesity. Treatment effects will be assessed for insulin sensitivity, blood pressure, blood lipids, muscle strength, and psychosocial predictors of strength training adherence. The innovation of this approach rests in its simplicity and the minimal time requirement for full participation (2 exercise sessions weekly). A preliminary study of this innovative approach resulted in 88% exercise session attendance over 12 months and maintenance of treatment effects on total body fat percentage to the end of pilot study measurements (9 months). This supports the feasibility and potential for long term efficacy of the proposed intervention approach. The long-term implication of success in this efficacy trial would be that this modest behavior change could prevent the fat gains and associated co-morbidities commonly observed in midlife women.