Overweight premenopausal Black and White women are randomized to either diet-only, diet+aerobic or diet+resistance exercise training. Diet/behavior intervention, with or without the aerobic or resistance exercise training, will be provided throughout the 18 months of study. Major outcomes will include measures of perceived and physiologic difficulty of exercise (cardiac, ventilatory, electromyographic responses to standardized exercise tasks); aerobic fitness; strength fitness; and spontaneous free-living energy expenditure (all derived from doubly labeled water). The results will provide insight into the effectiveness of, and the mechanisms by which, different types of exercise training can improve physical fitness, spontaneous engagement in physical activities of daily living and, in turn, weight-loss maintenance.