BACKGROUND: While there has been an explosion of mobile device applications (apps) promoting healthful behaviors, including physical activity and sedentary patterns, surprisingly few have been based explicitly on strategies drawn from behavioral theory and evidence. OBJECTIVE: This study provided an initial 8-week evaluation of three different customized physical activity-sedentary behavior apps drawn from conceptually distinct motivational frames in comparison with a commercially available control app. STUDY DESIGN AND METHODS: Ninety-five underactive adults ages 45 years and older with no prior smartphone experience were randomized to use an analytically framed app, a socially framed app, an affectively framed app, or a diet-tracker control app. Daily physical activity and sedentary behavior were measured using the smartphone's built-in accelerometer and daily self-report measures. RESULTS: Mixed-effects models indicated that, over the 8-week period, the social app users showed significantly greater overall increases in weekly accelerometry-derived moderate to vigorous physical activity relative to the other three arms (p values for between-arm differences = 0.04 to 0.005; social versus control app d = 1.05, CI 0.44 to 1.67; social versus affect app d = 0.89, CI 0.27 to 1.51; social versus analytic app d = 0.89, CI 0.27 to 1.51), while more variable responses were observed among users of the other two motivationally framed apps. Social app users also had significantly lower overall amounts of accelerometry-derived sedentary behavior relative to the other three arms (p values for between-arm differences = 0.02 to 0.001; social versus control app d = 1.10, CI 0.48 to 1.72; social versus affect app d = 0.94, CI 0.32 to 1.56; social versus analytic app d = 1.24, CI 0.59 to 1.89). Additionally, social and affect app users reported lower overall sitting time compared to the other two arms (p values for between-arm differences < 0.001; social versus control app d = 1.59, CI 0.92 to 2.25; social versus analytic app d = 1.89, CI 1.17 to 2.61; affect versus control app d = 1.19, CI 0.56 to 1.81; affect versus analytic app d = 1.41, CI 0.74 to 2.07). CONCLUSION: The results provide initial support for the use of a smartphone-delivered social frame in the early induction of both physical activity and sedentary behavior changes. The information obtained also sets the stage for further investigation of subgroups that might particularly benefit from different motivationally framed apps in these two key health promotion areas. TRIAL REGISTRATION: ClinicalTrials.gov NCT01516411.

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