Integrating Wearable Sleep Monitoring with Repeated Balance and Cognitive Testing: A Six-Week Longitudinal Observational Cohort and Feasibility Study Among Older Adults

Preserving functional independence is a primary goal of successful aging, yet the temporal dynamics linking sleep, motor balance, and cognition remain underexplored. This six-week longitudinal study evaluated the feasibility of continuous wearable sleep monitoring and unraveled the "Sleep-Balance-Cognition Triad" in 15 community-dwelling older adults. Sleep was tracked objectively via a consumer-grade wearable (Oura Ring) and subjectively via daily diaries. Motor function (Mini-BESTest, Timed Up and Go) and cognitive performance (NIH Toolbox) were assessed weekly. We evaluated both between-person habitual sleep traits and within-person acute temporal deviations using rolling multi-day windows. Results demonstrated exceptional feasibility for the wearable (100% compliance) compared to daily diaries (89.4%). Bland-Altman analysis revealed severe subjective sleep state misperception: participants systematically underestimated nocturnal awakenings by 64.9 minutes and overestimated total sleep time by 31.3 minutes. Habitual sleep consistency was protective of cognitive health, with longer average sleep strongly correlating with better working memory. Intra-individual analyses revealed a striking dissociation: while cognitive performance remained resilient to acute sleep deviations, motor systems exhibited dose-dependent vulnerability. Extended sleep and lethargy periods of 6 to 10 days or more significantly impaired dynamic balance and slowed functional mobility. In conclusion, sleep exerts a complex, dynamic impact on functional capacity. While long-term consistency buffers cognitive reserve, acute sleep fluctuations unmask progressive motor vulnerabilities. Furthermore, significant discrepancies in subjective recall highlight the clinical necessity of objective tracking. Continuous commercial wearables offer a highly feasible, actionable tool for the remote monitoring of fall risk and functional decline in older adults.