Associations between patient-reported functional disability and measures of physical ability in juvenile fibromyalgia

Juvenile fibromyalgia (JFM) is a chronic condition characterized by symptoms of pain and fatigue and is associated with sedentary behavior and functional disability. Adults with fibromyalgia exhibit deficits in physical fitness as evidenced by lower aerobic capacity and physical endurance, but it is unknown whether these impairments are apparent in adolescents with JFM. Furthermore, the extent to which functional disability and pain interference relate to measures of physical fitness has not been investigated in a pediatric pain population. During a baseline assessment for a clinical trial, 321 adolescents with juvenile fibromyalgia (M age = 15.14, 85.2% female) completed measures of pain intensity, fatigue, JFM symptom severity, functional disability, and pain interference. They also completed 2 validated fitness tasks: (1) the Harvard step test, which assesses aerobic fitness, and (2) the 6-minute walk test, a simple submaximal test of endurance. We examined associations among self-report measures and fitness assessments using bivariate correlations. We then employed hierarchical regression analyses to determine the unique contributions of physical fitness assessments to self-reported functional disability and pain interference. Results indicated that youth with JFM exhibited deficits in aerobic capacity and physical endurance. However, physical fitness explained negligible variance in functional disability and pain interference beyond that accounted for by pain, fatigue, and JFM symptom severity. Scores on available functional disability measures may reflect perceived difficulties in coping with symptoms during physical tasks rather than actual physical capability. Rigorous and sensitive assessments of physical fitness and endurance are needed to determine whether rehabilitation interventions for pediatric pain improve physical functioning.