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Fatigue-Related Changes in Torque Output and Electromyographic Parameters of Trunk Muscles During Isometric Axial Rotation Exertion: An Investigation in Patients With Back Pain and in Healthy Subjects

Ng, Joseph K.-F., PhD*†; Richardson, Carolyn A., PhD*; Parnianpour, Mohamad, PhD; Kippers, Vaughan, PhD

Exercise Physiology and Physical Examination
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Study Design.  A cross-sectional case–control study.

Objectives.  To examine the effect of fatigue on torque output as well as electromyographic frequency and amplitude values of trunk muscles during isometric axial rotation exertion in back pain patients and to compare the results with a matched control group.

Summary of Background Data.  Back pain patients exhibited different activation strategies in trunk muscles during the axial rotation exertions. Fatigue changes of abdominal and back muscles during axial rotation exertion have not been examined in patients with back pain.

Methods.  Twelve back pain patients and 12 matched controls performed isometric fatiguing axial rotation to both sides at 80% maximum voluntary contraction in a standing position. During the fatiguing exertion, electromyographic changes of rectus abdominis, external oblique, internal oblique, latissimus dorsi, iliocostalis lumborum, and multifidus were recorded bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were also measured.

Results.  No difference in the endurance capacity was found between back pain and control groups. At the initial period of the exertion, back pain patients demonstrated a statistical trend (P = 0.058) of greater sagittal coupling torque as well as lower activity of rectus abdominis and multifidus and higher activity in external oblique. During the fatigue process similar changes of coupling torque were demonstrated in both sagittal and coronal planes, but a smaller fatigue rate for right external oblique, increase in median frequency for latissimus dorsi, and lesser increase in activity for back muscles were found in the back pain group compared with the control group.

Conclusions.  Alterations in electromyographic activation and fatigue rates of abdominal and back muscles demonstrated during the fatigue process provide insights into the muscle dysfunctions in back pain and may help clinicians to devise more rational treatment strategies.

From the Departments of *Physiotherapy and

†Anatomical Sciences, University of Queensland, Brisbane, Queensland, Australia, and the

‡Department of Industrial, Welding and Systems Engineering, Ohio State University, Columbus, Ohio.

Supported by the Dorothy Hopkins Award for Clinical Study and the research support grant of Manipulative Therapists Special Group of Queensland, Australia.

Acknowledgment date: June 25, 2001.

Acceptance date: September 10, 2001.

Device status category: 1.

Conflict of interest category: 14.

Address correspondence to

Joseph K.-F. Ng, PhD

Department of Rehabilitation Sciences

The Hong Kong Polytechnic University

Hung Hom, Hong Kong

E-mail: rsjoseph@polyu.edu.hk

© 2002 Lippincott Williams & Wilkins, Inc.