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Different Ways to Balance the Spine: Subtle Changes in Sagittal Spinal Curves Affect Regional Muscle Activity

Claus, Andrew P., MPhty*; Hides, Julie A., PhD*; Moseley, G Lorimer, PhD†‡; Hodges, Paul W., PhD*

doi: 10.1097/BRS.0b013e3181908ead

Study Design. Exploratory study of regional muscle activity in different postures.

Objective. To detail the relationship between spinal curves and regional muscle activity.

Summary of Background Data. Sagittal balanced spinal posture (C7 above S1 in the sagittal plane) is a goal for spinal surgery and conservative ergonomics. Three combinations of thoracolumbar and lumbar spinal curves can be considered sagittal balanced postures: (i) flat—at both regions, (ii) long lordosis—lordotic at both regions, and (iii) short lordosis—thoracic kyphosis and lumbar lordosis. This study compares regional muscle activity between these 3 sagittal balanced postures in sitting, as well as a slump posture.

Methods. Fine-wire electromyography (EMG) electrodes were inserted into the lumbar multifidus (deep and superficial), iliocostalis (lateral and medial), longissimus thoracis, and transversus abdominis in 14 healthy male volunteers. Fine-wire or surface EMG electrodes were also used to record activity of the obliquus internus, obliquus externus, and rectus abdominis muscles. Root mean square EMG amplitude in the flat, long lordosis, short lordosis, and slump sitting postures were normalized to maximal voluntary contraction, and also to the peak activity across the sitting postures. Muscle activity was compared between postures with a linear mixed model analysis.

Results. Of the extensor muscles, it was most notable that activity of the deep and superficial fibers of lumbar multifidus increased incrementally in the 3 sagittal balanced postures; flat, long lordosis, and short lordosis (P < 0.05). Of the abdominal muscles, obliquus internus was more active in short lordosis than the other postures (P < 0.05). Comparing the sagittal balanced postures, the flat posture showed the least muscle activity (similar to the slump posture at most muscles examined).

Conclusion. Discrete combinations of muscle activity supported the 3 different sagittal balanced postures in sitting, providing new detail for surgeons, researchers, and therapists to distinguish between different sagittal balanced postures.

A variety of spinal curves achieve sagittal balanced spinal postures (C7 above S1). This study examined Electromyography at 5 spinal extensors and 4 abdominal muscles, whereas subjects sat in 3 combinations of thoracolumbar and lumbar spinal curves. The results provide new detail of specific muscle function with spinal curves.

From the *Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, The University of Queensland, School of Health and Rehabilitation Sciences, Brisbane, Australia; †Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, United Kingdom; and ‡Prince of Wales Medical Research Institute and School of Medical Sciences, The University of New South Wales, Sydney, Australia.

Acknowledgment date: June 9, 2008. Revision date: August 26, 2008. Acceptance date: September 8, 2008.

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

Federal, institutional, and foundation 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.

Supported by the National Health and Medical Research Council of Australia (to P.H.); The Nuffield Medical Research Fellowship from the University of Oxford (to G.L.M.). Reimbursement of study participants was funded by the The Dorothy Hopkins Award.

All procedures were approved by the University of Queensland Medical Research Ethics Committee, and written informed consent was obtained from all research subjects.

Address correspondence and reprint requests to Andrew Claus, MPhty, Division of Physiotherapy, School of Health and Rehabilitation Sciences, The University of Queensland, St. Lucia, Queensland 4072, Australia; E-mail:

© 2009 Lippincott Williams & Wilkins, Inc.