Our goal is to develop personalized decision rules for selecting the frequency, timing, and content of messages to promote physical activity. The objective of this project is to evaluate the acceptability and feasibility of two strategies for calibrating decision rules used to send those messages. Participants will wear an activity monitor for the collection of PA data and be randomly assigned to one of two adaptive intervention strategies. The decision rule for each participant will be refined on a monthly basis throughout the 6-month study based upon the accumulating data on how each participant is responding to different messages under different conditions. Our hypothesis is that more intensive intervention strategies will offer a better user experience because the resulting treatments will be experienced as more personalized.

Inclusion Criteria:

• Participants capable of reading, speaking and understanding English and of giving informed consent.
• Participants between the ages of 18-29 years.
• Participants must be free of visual impairment that would interfere with the receipt of text messages on their phone.
• Participants must be willing to wear a Fitbit Versa 3 almost continually (23.5 hours/day) for a 6- month period of time.
• Participants must own an iPhone or Android smartphone that they would be willing to download the custom Precision AIM and Fitbit app onto and sync with a Fitbit Versa 3.
• Participants interested in setting goals to increase their physical activity levels over the 6-month study.

Exclusion Criteria:

• Participants engaging in 150 or more minutes of moderate- or greater intensity PA /week as assessed by a research grade accelerometer.
• Participants engaged in organized programs with mandated physical activity (e.g., varsity sports, ROTC).
• Participants with contraindications to normal physical activity on the Physical Activity Readiness Questionnaire.
• Participants who require an assistive device for mobility or have any other condition that may limit or prevent participation in moderate-intensity physical activity.
• Participants who are pregnant or planning to become pregnant within the next 6 months.
• Participants with a prior diagnosis of cancer, cardiovascular disease, diabetes or metabolic syndrome.