The Effect of Chronic Low Back Pain on Trunk Muscle Activations in Target Reaching Movements With Various Loads

Study Design. A cross-sectional study of the timing of trunk muscle activations between 19 participants with chronic low back pain (LBP) compared with 19 matched controls. Objective. To determine the effects of target height and load on trunk muscle coordination in whole body reaching tasks, and whether participants with chronic LBP display a shift in trunk muscle coordination performing these tasks. Summary of Background Data. Changes in the precise timing of trunk muscle activation may cause an initial episode of back pain, or contribute to the development of recurrent or chronic symptoms. However, most paradigms used to examine timing of trunk muscle activation did not necessitate large displacements of the trunk. Methods. Participants with and without chronic LBP performed a series of bilateral reaching tasks to 3 target heights with 3 different loads held in the reaching hands. During reaching, joint motions were recorded with an optoelectric system and surface electromyographic signals were collected bilaterally from 5 trunk muscles: rectus abdominis, external oblique, internal oblique, iliocostalis lumborum, and the multifidis, and bilaterally from the deltoid muscle. The onset latencies of the antagonist trunk muscles relative to the deltoid muscle were analyzed to determine the effects of group, target height and load. Results. Onset of trunk extensor muscles was significantly delayed in participants with chronic LBP compared with control subjects. Further, the onset latency of the antagonist trunk muscles increased with target distance, but decreased with target load. Conclusion. These findings suggest that a well documented control strategy generalizes beyond single joint movements and that individuals with chronic LBP display a shift in this strategy.

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