The purpose of this study is to test the short-term effects of physical activity promotion messages designed for midlife adults. These messages are designed to provide information and motivation for physical activity by engaging key social processes, such as social comparison (i.e., self-evaluations relative to others).

This study will employ an intensive assessment procedure, in which participants are asked to complete several brief surveys per day via mobile device. On some days, as described below, survey content will be assigned with an embedded experimental design, administered via "micro-randomization" (i.e., randomization to receive one of multiple types of content at each momentary report). These methods allow for insight into the immediate effects of different types of content and their accumulated effects over the study period, as participants go about their normal activities.

Participants will complete an initial survey to assess their global and recent experiences (e.g., demographic information, social media use). Participants then will be asked to engage in 7 days of ambulatory data collection (i.e., as they go about their normal daily activities). This includes wearing pedometers to capture PA behavior (steps per day and aerobic-intensity PA) and completing 4 surveys per day via their smartphone.

A. For the first 3 days, surveys will assess each participant's preferences and responses to potential message content as they naturally occur. Content has been pre-tested in preliminary work. This will establish participants' baseline behaviors.

B. For the following 2 days, participants will be randomized at each survey to either: 1) make an upward PA comparison (to someone engaging in a lot of activity), 2) make a downward PA comparison (to someone engaging in very little activity), or 3) assess a different experience (e.g., received social support).

C. For the final 2 days, participants will be randomized at each survey to either: 1) informational messages about ways to increase activity, 2) encouragement to increase their activity in healthy ways, or 3) reminders about their activity goals.

Phases B and C will be counterbalanced, such that half of participants will receive prompts described in Phase B before Phase C, and half will receive prompts described in Phase C before Phase B.

Inclusion Criteria:

• Adult age 40-60 years old
• Sedentary (<150 minutes of moderate-intensity or 75 minutes of vigorous-intensity physical activity a week)
• One or more cardiovascular risk conditions (i.e., smoking, diagnoses of obesity. prediabetes/type 2 diabetes, prehypertension/hypertension, high cholesterol, metabolic syndrome)
• English language fluency
• Own a personal smartphone
• Have no medical or psychiatric contraindications to changing their physical activity (e.g., current injury, substance use disorder)

Exclusion Criteria:

• Not an adult age 40-60 years
• Not sedentary (≥150 minutes of moderate-intensity or 75 minutes of vigorous-intensity physical activity a week)
• No health conditions listed above (smoking, diagnoses of obesity, prediabetes/type 2 diabetes, prehypertension/hypertension, high cholesterol, metabolic syndrome)
• No English language fluency
• Does not own a personal smartphone
• Has medical or psychiatric contraindications to changing their physical activity (e.g., current injury, substance use disorder)

Self-identification as a woman, man, nonbinary, or other

Adults in midlife with elevated risk for cardiovascular disease (as defined by one or more of the following: smoking, diagnoses of obesity. prediabetes/type 2 diabetes, prehypertension/ hypertension, high cholesterol, or metabolic syndrome)