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Volume 42 Number 2, March/April 2005
Pages 235 — 250

Abstract - Electromyographic activity imbalances between contralateral back muscles: An assessment of measurement properties

Christian Larivière, PhD;1* Denis Gagnon, PhD;2 A. Bertrand Arsenault, PhD;3 Denis Gravel, PhD;3
Patrick Loisel, MD4

1Occupational Health and Safety Research Institute Robert-Sauvé, Montreal, Quebec, Canada; 2Department of Kinanthropology, University of Sherbrooke, Sherbrooke, Quebec, Canada; 3School of Rehabilitation, University of Montreal, Montreal, Quebec, Canada; 4Department of Surgery, Faculty of Medicine, University of Sherbrooke, Quebec, Canada
Abstract — Electromyographic (EMG) contralateral imbalances of back muscles are often interpreted as an aberrant back muscle pattern related to back pain. This study assessed different measurement properties (influence of the control of asymmetric efforts and of the force level, reliability, and sensitivity to low back status) of EMG imbalance parameters. Healthy controls (n = 34) and chronic low back pain subjects (n = 55) stood in a dynamometer measuring the principal (extension) and coupled (lateral bending, axial rotation) L5/S1 moments during isometric trunk extension efforts. The results showed that back pain subjects did not produce higher coupled moments than controls. Providing feedback of the axial rotation moment to correct asymmetric efforts during the task did not reduce EMG contralateral imbalances, except for some extreme cases. Normalized EMG imbalance parameters remain relatively constant between 40% and 80% of the maximal voluntary contraction. The reliability of EMG imbalance parameters was moderate, at best. Finally, neither low back status nor pain location had an effect on EMG contralateral imbalances. We conclude that the clinical relevance of EMG contralateral imbalances of back muscles remains to be established.
Key words: asymmetry, back pain, dynamometry, electromyography, force level, lumbar impairment, muscle imbalance, pain location, reliability, visual feedback.

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