Fatigability in Osteoarthritis: Effects of an Activity Bout on Subsequent Symptoms and Activity

Fatigue is a common symptom among older adults that is even more prevalent with increasing age (1,2,3,4). Fatigue has profound consequences on function and health (5) and has been associated with pain, sleep problems, depression, and increased mortality (2,3,6,7,8). Additionally, older adults who report fatigue are at greater risk for current and future disability in mobility and activities of daily living (9,10). Following engagement in fatiguing tasks, older adults have shown immediate decrements in balance and gait, which may in turn be related to a higher risk for falling (11). Despite its negative impact on daily life that may persist for years (12), fatigue in older adults has received little attention in research and clinical practice (4). In the interest of improving understanding of fatigue in older adults and developing clinical interventions, the National Institute on Aging introduced the concept of “fatiga-bility” or the ratio of subjective fatigue or tiredness to the frequency, intensity, or duration of activity (13). Thus, persons who are highly fatigable experience fatigue levels that are in some way activity limiting. Fatigue embedded within the context of daily activity is intended to discern how fatigue affects overall function instead of simply examining fatigability of a specific body system (eg, muscle fatigability [14] or aerobic capacity [15]). Various clinical populations (eg, chronic fatigue syndrome, cancer) are considered fatigable meaning fatigue is associated with reduced activity (16,17). In osteoarthritis (OA), over 40% of people aged 65 years and older have reported clinically important fatigue (6), and our team found that, compared with age-matched controls, people with OA were four times more likely to experience an increase in fatigue following a high bout of daily activity (18). Furthermore, examination of daily OA symptoms and activity revealed an inverse relation between fatigue and activity across a day. Although these results had ecological validity, it is unclear from these data what types of activity precipitated the fatigue increases, or how such activity altered subsequent fatigue, pain, and activity patterns. In addition, a comparison of changes in pain and fatigue related to activity was not examined, though pain, the cardinal symptom of OA, and a known correlate to fatigue (6,7,8,19) may play an important role in understanding fatigability in this population. The purpose of this study was to examine how standardized lab-based physical tasks designed to simulate activities of daily living and performed to the point of self-reported fatigue, affect subsequent fatigue, pain, and activity in older adults with hip and/or knee OA. We addressed the following research questions: Compared with a baseline period in which fatigue, pain, and activity were measured: Are fatigue and pain higher and activity lower in a 5-day period following performance of lab-based tasks (ie, are there carryover effects)? Are there differences in the diurnal patterns (within-day variation) of fatigue, pain, and activity following lab-based tasks? We hypothesized that there would be negative carryover effects in levels of OA symptoms and activity (ie, increased fatigue, pain, and decreased activity) after performance of lab-based physical tasks. We also hypothesized that diurnal patterns of OA symptoms and activity would be significantly altered following the lab-based tasks. Specifically, we expected to see reduced within-day variation of both symptoms and activity evidenced by higher and more stable symptom levels and lower and more stable activity levels. Due to the novelty of using simulated daily activities to induce fatigue in a controlled setting, the duration of the potential negative effects was unknown.