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

Thomas, James S., PhD, PT*; France, Christopher R., PhD; Sha, DaoHang, PhD*; Vander Wiele, Nicole, DPT*; Moenter, Stacey, DPT*; Swank, Kevin, BS*

doi: 10.1097/BRS.0b013e31815d0003
Occupational Health/Ergonomics
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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.

The timing and coordination of the trunk muscles of individuals with and without chronic low back pain are assessed using a target reaching paradigm. Participants with chronic low back pain had significantly longer latencies of the trunk extensor muscles compared with healthy matched controls. This suggests a shift in control strategy occurs with chronic low back pain.

From the *School of Physical Therapy, Ohio University, Athens, OH; and †Department of Psychology, Ohio University, Athens, OH.

Acknowledgment date: January 26, 2007. First revision date: May 1, 2007. Second revision date: July 16, 2007. Acceptance date: September 4, 2007.

This work was supported by National Institutes of Health Grant RO1-HD045512.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Federal funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

The authors of the manuscript have no financial or other relationships that might lead to a conflict of interest, and the study was conducted in accordance with the current American Psychological Association guidelines for human research and was approved by the Ohio University Institutional Review Board.

Address correspondence and reprint requests to James S. Thomas, PhD, PT, Ohio University School of Physical Therapy, W277 Grover Center, Athens, OH 45701; E-mail: thomasj5@ohiou.edu

© 2007 Lippincott Williams & Wilkins, Inc.