This study will test the effects of a social media game on the physical activity of older adult women. The game will consist of playful weekly challenges that require sharing photographs on a private social media group and also wearing an activity monitor to track steps. Participants will be randomized to this game group or to receive the activity monitor only.

Older adult women are at risk for negative health impacts of physical inactivity, but current strategies to increase their activity have had disappointing long-term results. The intervention tested in this study seeks to test an innovative intervention that targets older womens' perceptions of enjoyment and their personal identity and values. The investigators will test the efficacy of a 12-month social media-based physical activity intervention for sedentary older adult women. Participants will be randomized to receive a standard Fitbit-only intervention or to an enhanced Fitbit + weekly social challenges intervention. The investigators hypothesize that participants in the enhanced intervention will demonstrate greater increases in autonomous regulation and objectively-measured steps as compared to those in the standard intervention. The investigators will also measure outcomes after a 6 month maintenance period (18 months after beginning the intervention). Additional outcomes will include engagement with the social network and self-reported playful experiences.

Inclusion Criteria:

1. Female
2. Age between 65 and 85
3. Able to read and understand English
4. Willingness to be randomized to any condition
5. Daily availability of an iOS or Android mobile device that is capable of taking and sending photos
6. Willingness to use a private Facebook group
7. Sufficient internet access to post photos to Facebook at least once per week
8. Having an existing Facebook account or willingness to create one

Exclusion Criteria:

1. Unable to find transportation to the study location
2. Unable to walk for exercise (self-report)
3. Walk <475 meters in 6 minute walk test during baseline assessment
4. Stroke, hip fracture, hip or knee replacement, or spinal surgery in the past 6 months
5. Participant answered "yes" to any question on the PAR-Q+ and does not provide a doctor's note giving permission to begin a physical activity program
6. Self-reported weekly PA ≥ 150 minutes
7. BMI under 18 or over 40
8. Participant reports psychological issues that would interfere with study completion. Examples will be provided to illustrate potential psychological issues, such as dementia or schizophrenia.
9. Participant plans to move away from the Galveston-Houston area or to be out of town for more than 2 weeks at a time during the study period
10. Clinical judgment concerning safety
11. Currently participating in an organized commercial or research physical activity program
12. Uses a wearable activity monitor other than a simple pedometer and is unwilling to stop during the trial
13. Another member of the household is a participant or staff member on this trial

Participants must self-report as women

The investigators will provide access to all data, regardless of publication, collected as a part of this project. All external investigators must submit a written request identifying their research question(s) and specifying the data they would like to analyze. The request must include a data security plan and explanation of how the data will be stored and who will have access. All requests will be reviewed by the investigators in conjunction with UTMB's Institute for Translational Sciences key resources (in particular, the regulatory and ethics resources) to be sure appropriate NIH requirements are followed.

Data will only be available upon request

All external investigators must submit a written request identifying their research question(s) and specifying the data they would like to analyze. The request must include a data security plan and explanation of how the data will be stored and who will have access. All requests will be reviewed by the investigators in conjunction with UTMB's Institute for Translational Sciences key resources (in particular, the regulatory and ethics resources) to be sure appropriate NIH requirements are followed.