 The research team will conduct a 2 x 2 factorial experiment testing the individual and combined effects of two empirically and theoretically relevant sets of behavior change strategies on community-dwelling older adults physical activity. To do this the investigators will randomize participants 70 years old n 308 to 1 of 4 experimental conditions. All conditions include an evidence-based physical activity protocol endorsed by Centers for Disease Control and Prevention CDC for use by all older adults, including those with frailty and multiple co-morbidities and the commercially available physical activity monitor e.g., Fitbit to augment intervention delivery. Intervention components that are experimental and vary by condition are the sets of behavior change strategies which will be combined with the physical activity protocol and the physical activity monitor. Condition 1 has no specific behavior change strategies; Condition 2 includes an intervention component comprised of 5 interpersonal behavior change strategies, such as facilitating social support and social comparison; Condition 3 includes an intervention component comprised of 5 intrapersonal behavior change strategies, such as setting personally meaningful goals; and Condition 4 includes both sets of behavior change strategies -- 5 interpersonal strategies combined with 5 intrapersonal behavior change strategies. 