Abstract
Background
Full flexion lumbar postures maintained over a prolonged period of time have been
shown to lead to changes in the supporting passive structures of the spine and it
has been hypothesized that this may lead to low back pain/disorders. However, the
specific biomechanics and physiology of this link have not been fully developed. Of
particular interest is the interplay between the active and passive extensor mechanisms
and the role of rest break in this response.
Methods
Ten healthy participants performed a regimen of a 10-min full lumbar flexion followed
by a 10-min upright standing, with a slow speed isokinetic lift every 2.5 min. Changes in the full lumbar flexion angle (system creep) and the electromyographic
activity of back extensors in the isokinetic lifts were evaluated.
Findings
Results showed significant increases in the full flexion angle and increased activity
of the extensor muscles in the prolonged flexion to compensate for the reduced extension
moment producing capability of the passive tissues. A 30-s rest break in the middle
of the flexion moderated these viscoelastic responses.
Interpretation
The results suggest that prolonged lumbar flexion results in the systematic transfer
of an extension moment from passive tissues to active muscles. Heavy lifting or high
force exertion of back muscles immediately after prolonged flexion could be a risk
factor for low back disorders when the muscles lose their force generating capacity
due to passive stretching. This study also indicated the importance of sufficient
rest between consecutive full flexion tasks in reducing the risk.
Keywords
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Article info
Publication history
Published online: August 20, 2007
Accepted:
June 26,
2007
Received:
January 30,
2007
Identification
Copyright
© 2007 Elsevier Ltd. Published by Elsevier Inc. All rights reserved.
