Study design: A cross-sectional study of peak activation of trunk muscles in 20 participants with chronic low back pain.
Objective: To determine how pain-related fear influences peak activation of abdominal and trunk extensor muscles during maximal isometric trunk exertions.
Summary of background data: The pain adaptation model and the pain-spasm-pain model have been proposed to explain differences in trunk muscle activation between healthy participants and those with chronic low back pain. However, there is no clear consensus in the literature in support of either model, and there are no studies that have examined the role of pain-related fear on muscle activity in the context of these 2 models.
Methods: Participants with chronic low back pain performed a series of maximal isometric exertions into extension, flexion, rotation right and left, and side-bend right and left from a tall kneeling position with the spine in a neutral posture. A doubly multivariate MANCOVA was conducted with a between subject factor of group (high pain-related fear, low pain-related fear), a within subject factor of direction (extension, flexion, rotation left and right, side bend left and right), McGill Pain Questionnaire ratings entered as covariates, and peak EMG for all 10 trunk muscles entered as dependent variables.
Results: Averaged across all pull directions and all 10 trunk muscles assessed, participants with high pain-related fear had peak EMG that was only 49.5% of participants with low fear. Additionally, we found significantly smaller peak force for isometric exertions in flexion, side-bend right, and side-bend left directions.
Conclusion: Pain-related fear is associated with increased disability, in theory, because of avoidance behavior and disuse. Our data suggest that participants high in pain-related fear specifically avoid activation of the abdominal muscles during maximal isometric trunk exertions.