Objective Levels of Physical Activity and Performance and Selfreported Physical Function in Fibromyalgia (FM) Patients

Abstract

2097 Purpose: Interpretation of self-report physical function is confounded by a dearth of accurate and specific measures of physical activity and function. Patients' self-reports of physical function are likely obfuscated by illness beliefs and fear of ramifications. This study sought to determine if 2 surrogate measures of physical function (activity monitoring and submaximal exercise testing) were related to self-reported physical function in FM. Methods: Thirty-five FM patients (40.7 ± 9.6yr; 74% female) and 43 controls (CTL, 37.7 ± 9.1; 47% female) completed a submaximal bicycle test. The test consisted of continuous 3-min stages, culminating when HR reached 85% of agepredicted maximum. Peak exercise performance was de. ned as the highest wattage achieved. Of these subjects, 30 FM (41.5 ± 8.9; 77% female) and 29 CTL (38 ± 8.9, 48% female) also wore an activity monitor for 5 consecutive days and 4 nights. Activity was sampled in 30-sec epochs, averaged into 5-min intervals. Self-reported physical functioning was assessed via the SF-36 and the Multidimensional Fatigue Inventory. Results: Mean peak performance on the exercise test was lower for the FM group than CTL (98 ± 30 watts vs. 128 ± 43, p = 0.001). Average daytime and nighttime activity levels were similar between FM and CTL (daytime: 1456 ± 492 vs. 1445 ± 556 and nighttime: 147 ± 156 vs. 152 ± 107 activity units, respectively). However, peak activity was significantly lower in FM relative to CTL (7870 ± 3223 vs. 12178 ± 7862 activity units, p = 0.023), and was more variable. As expected, peak and average symptom ratings were higher in FM than CTL and SF-36 physical functioning scores were lower (SF-36 physical composite score: 35.6 ± 10.8 vs. 55.8 ± 5.4, p = 0.00). However, none of these variables were related to average or peak activity levels. No objective measure of activity (peak exercise performance or peak or average activity) was correlated with any self-report measure of function, or symptoms, in either the patient or control group (r's = −.05 to 0.23). Conclusions: FM patients report the lowest physical function among almost all rheumatic illnesses. Despite this, FM patients in this study were able to maintain a “normal” average level of activity relative to the controls, albeit with considerably greater variability. Peak physical function as evaluated by 2 different measures was not related to self-reported physical function in either FM or CTL. These observations suggest that factors other than pure physical movement influence selfreported functioning, and support the notion that peak activity levels and peak exercise performance are indices of “capacity” rather than indices of day-to-day patient ability.