Reduced Trunk Coupling in Persons With Recurrent Low Back Pain Is Associated With Greater Deep-to-Superficial Trunk Muscle Activation Ratios During the Balance-Dexterity Task

Background Motor control dysfunction persisting during symptom remission in persons with recurrent low back pain (LBP) may contribute to the recurrence of pain. Objectives To investigate trunk control in persons in remission from recurrent LBP and in back-healthy controls using a dynamic, internally driven balance task. No differences in task performance were expected between groups, but it was hypothesized that persons with recurrent LBP would exhibit greater trunk coupling, consistent with a trunk-stiffening strategy. Methods In this cross-sectional controlled laboratory study, persons with and without recurrent LBP (n = 19 per group) completed the balance-dexterity task, which involved balancing on one limb in standing while compressing an unstable spring with the other. Task performance measures included center-of-pressure velocity under the stance limb and vertical force variability under the spring. Trunk coupling was quantified with the coefficient of determination (R 2 ) of an angle-angle plot of thorax-pelvis frontal plane motion. Fine-wire and surface electromyography captured activations of paraspinals and abdominals. Results There were no differences between groups for any task performance measure. The group in remission from recurrent LBP exhibited reduced trunk coupling, or more dissociated thorax and pelvis motion, compared to the healthy control group (P = .024). Trunk coupling in this group was associated moderately with the lumbar multifidus-to-erector spinae activation ratio (r = 0.618, P = .006) and weakly with the internal oblique-to-external oblique ratio (r = 0.476, P = .046). Conclusion The balance-dexterity task is a submaximal, internally driven unstable balance task during which more dissociated trunk motion was observed in persons in remission from recurrent LBP. Findings underscore the task-dependent nature of trunk control research and assessment in persons with recurrent LBP. J Orthop Sports Phys Ther 2019;49(12):887–898. Epub 15 May 2019. doi:10.2519/jospt.2019.8756