Background/Purpose: Fibromyalgia (FM) is a chronic multidimensional disorder that causes physical and psychological impairment, incurring significant healthcare costs. Self-efficacy and pain catastrophizing have been shown consistently to predict disability in chronic pain populations. However, the extent and the mechanism of their impact on physical functioning in people with FM are yet unclear. The purpose of this study is to examine if self-efficacy and pain catastrophizing are associated with both self-reported and performance-based physical functioning in individuals with FM. We also explore the potential of the overall impact of FM as a mediator.

Methods: We analyzed the baseline data from a randomized controlled trial comparing the effects of Tai Chi and aerobic exercise in individuals meeting both the 1990 and 2010 ACR Criteria for FM. Participants completed the 8-Item Arthritis Self-Efficacy Scale modified for FM (ASES-8, range 0-10), Catastrophizing subscale of the Coping Strategies Questionnaire (CSQ-CAT, range 0-42), 36-Item Short-Form Health Survey Physical Functioning scale (PF-10, range 0-100), and the Revised Fibromyalgia Impact Questionnaire (FIQR, range 0-100), with higher scores indicating higher levels of the respective constructs measured, as well as the 6-Minute Walk Test (6MWT, measured in meters). Pearson correlation and multivariate linear regression analyses were used to test for associations. We also performed mediation analyses (Baron and Kenney with Sobel test and bootstrapping) using the FIQR as a mediator.

Results: We included 224 participants (mean age: 51.8 years [SD=12.0]; mean BMI: 30.7 kg/m² [SD=6.7]; 92.9% women; 61.2% white; 22.3% black). ASES-8 and CSQ-CAT were significantly associated with PF-10 (r= 0.25 and -0.30 respectively, both p<0.001) and with 6MWT (r=0.17 and -0.14 respectively, p=0.01 and 0.04 respectively). When adjusted for age, gender, obesity, and education, only the association between CSQ-CAT and 6MWT became insignificant (p=0.06). In addition, mediation analyses revealed that the FIQR attenuated the associations of ASES-8 and CSQ-CAT with PF-10 and 6MWT (see Figure).

Conclusion: Our study shows that, while FM patients’ belief in the ability to manage FM-related symptoms and the tendency to catastrophize pain may shape the perception of his or her physical capacity and also influence the level of physical performance, they may not independently predict physical functioning in individuals with FM. The results of the mediation study show that the overall impact of FM, often viewed as a dependent variable, attenuates the associations between the cognitive constructs and physical functioning, suggesting its potential as a mediator. Future longitudinal studies designed to verify the directionality of the relationships are warranted.