Approximately 69% of the U.S. adult population is overweight, defined by a body mass index (BMI) of ≥ 25.0 kg/m2, and 35% are obese (BMI ≥ 30.0 kg/m2), with the prevalence of overweight and obesity rising drastically over the past several decades. Adults who are overweight or obese are typically recommended to change lifestyle factors (e.g. diet, physical activity, etc.) to lose weight and improve health. When evaluating the effects of these lifestyle changes on weight and health in a research setting, physical activity is supervised (i.e. physical activity completed in a health-fitness facility with direct supervision from trained staff). With supervised physical activity, researchers are able to quantify the frequency, intensity, duration, and type of physical activity. Thus, supervised physical activity is considered the gold-standard when evaluating the effects of physical activity on weight and other physiological parameters. However, the results of supervised physical activity trials may not translate to clinical settings. A typical clinical approach prescribes physical activity in an unsupervised manner (i.e. physician tells patient to be more physically active or take more steps/day). Unsupervised physical activity can be done in any environment or at any time that best suits the individual. Knowing the effects of unsupervised physical activity is important because of the translation of this type of physical activity to non-research settings. Therefore, knowing the magnitude of the physiological effects of unsupervised physical activity compared to supervised physical activity at the same prescribed intensity and dose is of clinical and public health importance especially in an overweight and obese population. This study is designed to provide insight on these important research questions that can inform future research and the application to clinical, public health, and health-fitness settings.

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.