Examination of patient-reported, performancebased, and accelerometer-based outcome measures of physical function in adults with fibromyalgia

Assessment of physical functioning is critical for evaluating treatment effectiveness. Patient‐reported and performance‐based measures of physical functioning are commonly used in clinical trials of chronic pain treatments, but there is growing interest in the application of accelerometer devices to objectively measure physical activity and track movement patterns over time. All three measurement approaches have different strengths and weaknesses, but the relationships between patient‐reported, performancebased, and accelerometer‐based measures of physical functioning are not well understood. Accordingly, we analyzed baseline data from an ongoing randomized clinical trial of 144 adults with fibromyalgia, a condition characterized by chronic widespread pain. Participants wore a uniaxial accelerometer on the wrist for >= 5 days, recording an integrated measure of motion over 15‐second epochs at 32 Hertz. Pearson correlation coefficients were computed between accelerometer‐measured daily activity counts per minute (CPM), distance walked during a performancebased 6‐minute walk test (6MWD), and patient‐reported physical functioning (PROMIS‐29 subscale) and pain interference with functioning (Revised Fibromyalgia Impact Questionnaire [FIQR] and PROMIS‐29 subscale). The mean (+/‐SD) age of the participants was 49.5 (+/‐12.6) years and 93% were women. Participants had a mean 6MWD of 421.2 (+/‐96.5) meters, mean FIQR function score of 15.2 (+/‐6.8), and mean PROMIS pain interference and physical function scores of 62.9 (+/‐5.7) and 37.6 (+/‐4.6), respectively. Additionally, the average daily CPM (excluding sleep intervals) was 243.4 (+/‐89.0). The correlations between CPM, 6MWD, and patient‐reported FIQR and PROMIS measures ranged from .27‐.46. These low to moderate correlations indicate that patient‐reported, performancebased, and accelerometry‐based measures assess different aspects of physical functioning: (1) perceived abilities, (2) objective physical capacity in a standardized environment, and (3) real‐world, daily activity patterns. Thus, results from the current study suggest that a combination of different functional assessment methods may be useful to evaluate treatment effectiveness as they measure complementary but unique aspects of physical functioning.