Delayed abdominal muscle onsets and self-report measures of pain and disability in chronic low back pain

Objective: The objective of this study was the measure the onset time of the transverse abdominis (TA) muscle during rapid unilateral shoulder movements in individuals with chronic low back pain (LBP), and to evaluate the relationship between latency times and self-report measures of pain and disability. Design: Descriptive cross-sectional study. Setting: University laboratory. Participants: Eighty individuals with chronic LBP of a non-specific origin (males n = 44, females n = 36). Main outcome measures: Responses of the right and left surface TA/ internal obliques were measured using surface electromyography (EMG) during rapid unilateral shoulder flexion, abduction, and extension. Pain intensity was measured using a visual analog scale (VAS), and disability with the Oswestry disability index (ODI). Results: Seventy-five percent of individuals were identified as lacking feedforward activation. A significant side x direction main effect was identified, with the ipsilateral latency more delayed in flexion and abduction (F(2316) = 58.2, p < 0.001). Individuals without feedforward activation had lower ODI scores (23.2 +/- 6.9% vs 31.0 +/- 9.2%, mean difference 7.8%, 95% CI 3.9 to 11.6%, p < 0.001). Regression analysis found that 17% of the variance in VAS scores for the entire sample (n = 80) were explained by the latency times measured. This relationship was stronger when the sample was separated into individuals who did (n = 20), and did not (n = 60) have feedforward activation. Conclusion: Deep abdominal muscle onsets during rapid limb movement were significantly associated with self-rated pain scores. Seventy-five percent of individuals with chronic non-specific LBP exhibited delayed activation. No evidence has been provided in this study to support, or refute the use of specific localized deep abdominal contractions for exercise rehabilitation programs. (C) 2009 Elsevier Ltd. All rights reserved.