Sleep and functional capacity in adults: Cross-sectional associations among self-report and objective assessments

Objectives: This study examined the relationship between self-reported and objectively measured sleep and functional capacity in adults.

Design: Cross-sectional.

Participants: Data were from the Midlife in the United States study. The sample consisted of men and women (n = 664) aged 25-83 who completed telephone interviews, questionnaires, and an overnight clinic stay.

Measurements: Sleep was assessed by self-report (Pittsburgh Sleep Quality Index [PSQI]) and by objective measures (sleep latency, duration, wake after sleep onset [WASO], and midpoint/midpoint variability) from 7 consecutive days of actigraphy. Functional capacity was assessed by self-report of limitations and measured gait speed, grip strength, and chair stands.

Results: In linear regression models adjusting for demographic and health factors, better self-reported sleep quality predicted fewer reported limitations, stronger grip, quicker gait, and faster chair stands (all P< .01). Greater WASO predicted more self-report limitations and slower gait speed (P< .05). Long (>8 hours) sleep duration and a more variable sleep schedule predicted lower grip strength (p < .05). Finally, after adjustment for objective sleep measures, PSQI remained a significant predictor of functional measures (P< .05) and explained a significant amount of additional variance (change in R²: 0.01-0.05).

Conclusions: The present results suggest that subjective and objective sleep measures capture distinct aspects of sleep that are independently related to functional capacity. The variance in functional measures explained by sleep variables, though small, was comparable to other risk factors for functional impairment (eg, obesity), underscoring the importance of associations between sleep and optimal function in adults.