Pain-Related Fear, Lumbar Flexion, and Dynamic EMG Among Persons With Chronic Musculoskeletal Low Back Pain

OBJECTIVES: The purpose of this study was to examine the relationship between pain-related fear, lumbar flexion, and dynamic EMG activity among persons with chronic musculoskeletal low back pain. It was hypothesized that pain-related fear would be significantly related to decreased lumbar flexion and specific patterns of EMG activity during flexion and extension. STUDY DESIGN: Data was obtained from subjects who, on a single day, completed self-report measures of pain and pain-related fear, and were interviewed to determine demographic and pain information. Subjects then underwent a dynamic EMG evaluation for which they were asked to stand, then bend forward as far as possible, stay fully flexed, and return to standing. Lumbar EMG and angle of flexion were recorded during this time. A flexion-relaxation ratio (FRR) was computed by comparing maximal EMG while flexing to the average EMG in full flexion. SUBJECTS: Seventy-six persons with chronic musculoskeletal low back pain. RESULTS: Zero-order correlations indicated that pain-related fear was significantly related to reduced lumber flexion (r = -0.55), maximum EMG during flexion (r = -0.38) and extension (r = -0.51), and the FRR (r = -0.40). When controlling for pain and demographic factors, pain-related fear continued to be related to reduced lumbar flexion. Using a path-analytic model to examine whether angle of flexion mediated the relationship between fear and EMG activity, the models examining maximal EMG during flexion and extension supported the notion that pain-related fear influences these measures indirectly through its association with decreased range of motion. Conversely, pain-related fear was independently related to higher average EMG in full flexion, while angle of flexion was not significantly related. Pain-related fear was directly related to a smaller FRR, as well as indirectly through angle of flexion. CONCLUSIONS: Pain-related fear is significantly associated with reduced lumbar flexion, greater EMG in full flexion, and a smaller FRR. The relationship between pain-related fear and EMG during flexion and extension appears to be mediated by reduced lumbar flexion. These results suggest that pain-related fear is directly associated with musculoskeletal abnormalities observed among persons with chronic low back pain, as well as indirectly through limited lumbar flexion. These musculoskeletal abnormalities as well as limited movement may be involved in the development and maintenance of chronic low back pain. In addition, changes in musculoskeletal functioning and flexion associated with pain-related fear may warrant greater attention as part of treatment.