Self-reported physical function is strongly related to pain behavior and pain interference and weakly related to physical capacity in people with chronic low back pain

Background: Inclusion of self-reported and capacity-based measures may help to further elucidate the interactive link between how people think and move. Objective: To characterize the relationship between self-reported factors of physical function and pain with objective physical capacity measures. Design: Cross-sectional study of 328 adults with chronic low back pain (CLBP). Method: Spearman correlations assessed the relationship between pairs of measures. Multiple linear regression models assessed the association between self-reported measures of physical function and the grouping of physical capacity measures. Self-reported measures included Roland Morris Disability Questionnaire (RMDQ), PROMIS Physical Function, Pain Behavior, and Pain Interference; Fear-Avoidance Beliefs Questionnaire (FABQ), Pain Catastrophizing Scale (PCS), and Chronic Pain Acceptance Questionnaire (CPAQ). Capacity measures included walking speed and endurance, lower extremity functional strength, lumbopelvic range of motion, and trunk endurance. Results: PROMIS Physical Function was directly and weakly correlated with walking speed (p = 0.26, 2-min walk) and inversely and weakly correlated with lower extremity strength (p =-0.29, 5x sit-to-stand). RMDQ was not correlated with any of the capacity-based measures. PROMIS Physical Function was inversely and moderately correlated with Pain Interference (p =-0.48) and Pain Behavior (p =-0.43), PCS (p =-0.36), and FABQ (p = -0.31). The RMDQ was strongly correlated with PROMIS Physical Function (p =-0.56), Pain Behavior (p = 0.51) and Pain Interference (p = 0.49); and moderately correlated with PCS (p = 0.37) and FABQ (p = 0.33). PROMIS Physical Function and RMDQ were not correlated with CPAQ. Lower scores on PROMIS Physical Function were weakly associated with lower measures of lower extremity strength (-0.30, 95% CI:-0.51 to -0.09, p = 0.005). Higher scores on RMDQ were also weakly associated with lower measures of lower extremity strength (0.26, 95% CI: 0.11 to 0.41, p = 0.001). Conclusions: A strong association emerged between self-reported limitations in physical function, pain behavior, and pain interference. A weak association emerged between self-reported physical function and lower extremity strength.