Fatigued, but Not Frail: Perceived Fatigability as a Marker of Impending Decline in Mobility-Intact Older Adults

Objectives: To evaluate perceived fatigability as a predictor of meaningful functional decline in non-mobility-limited older adults. Design: Longitudinal analysis of data from the Baltimore Longitudinal Study of Aging (BLSA). Setting: National Institute on Aging, Clinical Research Unit, Baltimore, Maryland. Participants: Men and women aged 60 to 89 participating in the BLSA with concurrent perceived fatigability and functional assessments and follow-up functional assessment within 1 to 3 years (N = 540). Measurements: Perceived fatigability was ascertained using the Borg rating of perceived exertion (RPE) after 5 minutes of treadmill walking at 1.5 miles per hour. Functional assessments included usual and fast gait speed, the Health, Aging and Body Composition physical performance battery (HABC PPB) and reported walking ability. Reported tiredness and energy level were examined as complementary predictors. Covariates included age, age squared, race, follow-up time, and baseline function. Meaningful decline was defined as 0.05 m/s per year for usual gait speed, 0.07 m/s per year for fast gait speed, 0.12 points/year for HABC PPB, and 1 point for walking ability index. Results: Over a mean 2.1 years, 20–31% of participants declined across functional assessments. Fatigability was associated with a 13–19% greater likelihood of meaningful decline in all measures (P = .002–.02) per 1-unit RPE increase. After considering tiredness and energy level separately, findings were essentially unchanged, and neither was associated with gait speed or physical performance decline. In contrast, each separately predicted decline in reported walking ability independent of fatigability (P = .03 and P < .001, respectively). Conclusion: Routine assessment of fatigability may help identify older persons vulnerable to greater-than-expected functional decline.