Participants will be randomized to one of three groups: supervised physical activity prescribed in min/week (SUP-PA), unsupervised physical activity prescribed in min/week (UNSUP-PA), and unsupervised physical activity prescribed in steps/day (STEP). Participants in all three groups will participate in a behavioral weight loss intervention which includes dietary counseling and weekly group sessions during the 12-week program. SUP-PA will be prescribed 150 minutes/week of moderate-to-vigorous physical activity (MVPA) completed under direct supervision of trained staff at a designated health-fitness facility. UNSUP-PA will be prescribed a physical activity dose matched to SUP-PA. STEP will be prescribed a 10,000 step/day recommendation with 2,500 of those steps completed at a "brisk" pace. The primary aim of this study is to compare the effects of all three groups on moderate-to-vigorous physical activity (MVPA) accumulated in bouts of at least 10 minutes. The primary outcome will be assessed at baseline, week 4, week 8, and week 12. Secondary aims of this trial include comparing light intensity physical activity, sedentary time, cardiorespiratory fitness, weight, body composition, waist circumference measures, physical activity self-efficacy, blood pressure, and dietary intake across all three groups. Secondary aims will be assessed at baseline and week 12.