Interested participants will schedule and complete a phone screen with a researcher to determine eligibility, and if deemed eligible, will complete an initial hour-long baseline assessment with a member of the study team. The baseline assessment will be conducted over video call using the secure, easy-to-use and HIPAA-compliant Zoom service hosted by Drexel University. During the baseline assessment, the assessor will electronically obtain the participant's informed consent to participate in the study, guide the participant on using a mobile phone application to track their daily steps (Google Fit), verbally provide participants with psychoeducational content on safely increasing their physical activity, and administer a psychological task (Implicit Association Test) as well as questionnaires (Demographics; Physical Activity Enjoyment Scale; Treatment Self-Regulation Questionnaire; Self-Efficacy for Exercise Scale). Immediately following the assessment, participants will be randomized to receive one of two possible remote physical activity interventions: adaptive goal-setting (AGS) or static goal-setting (SGS). Randomization will follow a stratified procedure based on age (cutoff point = 45 years), and permuted block randomization will be used within strata to assign individuals to an intervention condition (AGS or SGS). Both interventions will be preceded by a 10-day baseline "run-in" period during which participants will be asked to record their activity but will not receive any daily step goals. In addition, in both interventions, a brief (10-minute) mid-study (3-week) check-in call will be conducted with each participant by a member of the study team to encourage continued compliance with step goals and problem-solve any barriers to increasing physical activity. Participants will also complete a brief survey once each week over the course of the intervention period. At the conclusion of the intervention period, participants will complete several post-intervention questionnaires/tasks and will then be compensated for their participation.

Participants in the adaptive goal-setting condition will begin receiving a new step goal each day over text message (SMS) following the baseline run-in period (starting Week 2). These messages will continue to be delivered each day for the entire duration of the 6-week intervention period (through Week 8), and will contain information about the participant's daily-assigned step goal as well as their number of steps on the previous day in reference to their previous day's goal. Goals will be calculated using a 60th percentile method (consistent with prior research on adaptive goal-setting), such that each day's goal will be set to the 60th percentile value of the last 9 days of available step data for that participant. Goals will be calculated by an algorithm stored on a remote database that automatically extracts user data from the Google Fit cloud server (Google Fitness Store). The database will store daily steps data for each participant, use these data to calculate new daily step goals and transmit them over SMS using a commercial cloud communications platform. The maximum steps goal permitted by the algorithm will be 20,000 steps/day, to ensure that goals remain within an attainable range for most individuals. Participants in the static goal-setting condition will receive the same exact step goal each day (10,000 steps), consistent with prior research, and will receive daily text message updates providing a summary of their previous day's steps and encouraging them to reach their 10,000-step goal for that day.