This study is a two-arm, single-site randomized controlled trial to test whether a four-week technology-based intergenerational social motivation intervention enhances physical activity in 60 cognitively unimpaired older adults with a first-degree history of Alzheimer's disease. These at-risk older adults will be recruited as a subgroup from a longitudinal cohort at McGill University, PREVENT-AD. At the outset, half of the participants will be randomized to the intergenerational social motivation condition (intervention group) and the other half will be randomized to the control group (1:1). A multimodal AD risk score based on older participants' already acquired AD biomarker, health and cognitive data will be used as strata for randomization to ensure equal assignment of high-risk participants to Intervention and control groups, using a permuted block method with random blocks.

The primary outcome is an increase in step count as measured by accelerometer. Secondary outcomes are an increase in total physical activity, mood, generativity, cognition, and loneliness. After an initial visit consisting of behavioral testing and structural and functional MRI, participants in the intervention group will be paired with younger adults (14 to 40 years) to form intergenerational dyads. Younger adults are either a family member of the older adult or a younger adult recruited from the community. Participants in the intervention group will receive personalized, positive daily messages over a four-week period via their device using the 'Our Family Garden' technology platform. These daily messages combine (1) pro-social goals (donation to charity after reaching exercise goals), (2) intergenerational social engagement, and (3) positive personalized messages from their younger study partners. This study will have 6 visits over a 2-month period in addition to the four-week intervention period (3 months total). Cognitive and behavioral data will be collected at each visit and physical activity data will be collected over the intervention period.

The primary endpoint is defined as the end of the initial period. Data collected are stored in one of three ways; (1) Physical activity monitoring data are extracted from their respective software packages and uploaded directly to a secure data storage environment at a high-performance computing facility. All pen-and-paper psychosocial and neuropsychological assessments are scored and entered in REDCap. Computerized psychosocial assessments are collected directly in REDCap and computerized neuropsychological assessments are entered in REDCap. TextMagic is used to distribute the daily intervention messages. Collected and anonymized survey data are stored on the web application behind an administrative login developed with Django, a high-level Python web framework. All data from REDCap will be exported to CSV files using the data de-identification feature for subsequent analysis with R and SPSS statistical analysis packages. After compiling all data across the 3 different data servers, data will be checked for completeness and correctness using frequency distributions (for missing data and out-of-range values). For the final dataset, the multiple imputations by chained equations (MICE) will be used to input missing values with 10 imputations.