Abstract
OBJECTIVES: To document the stability, concurrent validity, and clinical correlates of two fatigability severity measures as recommended by the American Geriatrics Society. DESIGN: Descriptive, cross-sectional. SETTING: Two independent living and one community senior centers. PARTICIPANTS: Forty-three participants, with an average age 85 ± 6. MEASUREMENTS: Perceived fatigability severity was quantified by directly asking participants to report change in energy after a standardized 10-minute walk at a self-selected pace. Performance fatigability severity was defined as a ratio of change in walking speed to total distance walked. The walk test was repeated within 2 weeks to assess stability. Total daily physical activity (PA) was measured over 7 consecutive days using a waist-worn accelerometer. Frailty was measured using the Vulnerable Elders Survey interview scale, and gait speed was measured using a standardized 25-feet walk test. RESULTS: The perceived and performance fatigability severity measures were significantly correlated (correlation coefficient (r) = 0.94, P < .001) and stable over two assessments (r = 0.82 and 0.85, P < .001). Both fatigability severity measures were significantly correlated with PA level (r = -0.42 and r = -0.44, respectively, P = .02), frailty (r = 0.47 and 0.53, respectively, P = .001) and gait speed (r = -0.45, P = .003 and r = -0.54, P = .001, respectively). CONCLUSION: The methodology described in this study permits the calculation of two highly correlated fatigability severity scores, which summarize the relationship between a person's change in self-reported tiredness or change in physical performance and concurrently measured PA. The fatigability severity scores are reproducible and correlated with clinical measures predictive of decline. The methods used to quantify fatigability severity can be implemented during a brief assessment (<15 minutes) and should be useful in the design and evaluation of interventions to increase PA in older adults at risk of functional decline.