Fatigue in older adults is associated with functional decline and reduced participation in daily life; however, it is not well characterized. Examining fatigue within activity performance, or "fatigability," is a recommended approach to begin to understand fatigue and its underlying mechanisms. This study examined the construct validity of lab-based measures of fatigability and compared these measures with fatigability in daily life (termed ecological fatigability).
Participants with osteoarthritis and fatigue (n = 163) underwent laboratory assessments, completed questionnaires, and wore accelerometers for 7 days while tracking symptoms and behaviors. Lab-based fatigability measures were quantified using the 6-minute walk test. Perceived fatigability was assessed by asking participants before and after the test to report: (i) fatigue severity and (ii) perceived exertion. Performance fatigability was calculated using change in walking speed divided by total distance walked. Ecological fatigability was calculated from the 7-day assessment in which fatigue severity was reported five times a day and physical activity was continuously measured. Additional ecological measures (eg, self-pacing) were examined.
Lab-based perceived and performance fatigability measures were highly inter-correlated, moderately correlated with gait speed and metabolic measures, and weakly correlated with physical activity. Although ecological fatigability was weakly correlated with lab-based measures, participants with high fatigability on lab-based measures demonstrated more self-pacing behaviors than participants with low fatigability.
Lab-based fatigability measures are related to physical capacity measured both in the lab and daily life. Lab-based fatigability measures provide important information regarding daily life fatigability useful for future intervention development.