Validation of SAUDE: A Citizen Science App for Functional Balance Assessment in Older Adults

Background: Citizen science (CS) can broaden participation and support knowledge co-production in health research. However, its application in rehabilitation remains limited, particularly with respect to the validation of tools for functional assessment and fall-risk monitoring. Objective: To validate SAUDE, a mobile application designed to support citizen-led assessment of balance and mobility, and to examine its usability among older adults. Methods: A cross-sectional mixed-methods study was conducted with 47 community-dwelling older adults. Participants independently performed three standardized functional tests—Timed Up and Go (TUG), 30-second Sit-to-Stand (STS), and Single-Leg Stance (SLS)—using the SAUDE app, while simultaneous in-person assessments were conducted by a trained evaluator. Criterion validity was examined using concordance correlation coefficients (CCC). Convergent validity was assessed through inter-test correlations, and construct validity through associations with self-reported fall history. Usability observations were collected during testing. Results: Strong agreement was observed between app-based and assessor-based measurements for all tests (CCC [95% CI]: TUG = 0.893 [0.836, 0.932], STS = 0.977 [0.960, 0.987], SLS = 0.955 [0.922; 0.974]). Inter-test correlations supported convergent validity, and moderate associations between TUG performance and fall history provided evidence of construct validity. Most participants completed the assessments independently, although visual, cognitive, and motor limitations affected interaction with the app in some cases. Conclusions: SAUDE demonstrated validity and usability as a citizen science platform for self-assessment of functional mobility in older adults. Its open-access design and integration of fall-related outcomes support its potential for community-based health monitoring. Further development should focus on accessibility enhancements, data handling optimization, and evaluation in larger, real-world settings to advance inclusive rehabilitation strategies.