Fatigue and Fatigability in Older Adults

Fatigue is believed to be a common complaint among older adults; however, multiple studies of self-reported fatigue across the lifespan have found this may not be the case. To explain this paradox, this article considers “fatigability”–a phenotype characterized by the relationship between an individual's perceived fatigue and the activity level with which the fatigue is associated. Fatigability may be measured by combining self-report measures of fatigue with performance of physical or cognitive activities, provided that the work of the activity is known or can be standardized. Doing so prevents self-pacing and allows meaningful comparisons across subjects and between studies. Increased fatigability with aging may arise from a variety of factors including age-related changes in energy production or utilization, and inflammatory mechanisms. A few published intervention studies have targeted fatigue in older adults, though none have examined fatigability specifically. Because fatigue may represent a physiologic warning system, future clinical studies may benefit from a focus on fatigability, where both symptoms and function are considered.