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Muscular and kinematic behavior of the lumbar spine during flexion-extension.

Journal article
Authors Allison Kaigle Holm
Per Wessberg
Tommy H. Hansson
Published in Journal of spinal disorders
Volume 11
Issue 2
Pages 163-74
ISSN 0895-0385
Publication year 1998
Published at Institute of Surgical Sciences, Department of Orthopaedics
Pages 163-74
Language en
Keywords Adult, Biomechanics, Electromyography, Female, Human Experimentation, Humans, Joint Instability, physiopathology, Low Back Pain, physiopathology, Lumbosacral Region, physiology, Male, Middle Aged, Movement, Muscle, Skeletal, physiology, Posture
Subject categories Orthopaedics


Reduction in lumbar muscular activity at full body flexion, known as flexion relaxation, has been studied in relation to overall trunk, lumbar spine, and hip flexion, but has not been evaluated in conjunction with motion on the segmental level. In this study, intervertebral motion in a lumbar motion segment, trunk flexion, and the electromyographic activity in the lumbar erector spinae muscles were simultaneously measured during dynamic flexion-extension in seven patients with chronic low back pain with symptoms suggesting segmental instability and in six asymptomatic controls. A linkage system, which attached directly to the spinous processes of a lumbar motion segment, was used to continuously measure the sagittal plane intervertebral motion, while a potentiometric goniometer measured trunk flexion; myoelectric activity was measured using surface electrodes. It was found that intervertebral motions, as well as trunk mobility, were significantly less in the patients, both in terms of range and pattern of motion. Flexion relaxation was demonstrated in the controls by a 78% decrease in myoelectric activity at full flexion, whereas in the patients, only a 13% reduction was found, with most of the patients experiencing no reduction at all. Flexion relaxation occurred only in subjects in whom intervertebral rotation had reached a stage of completion considerably before full trunk flexion was achieved. These findings suggest that persistent muscle activation, which restricts intervertebral motion, is a means by which the neuromuscular system provides stability to help protect diseased passive spinal structures from movements that may cause pain.

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