THE INFLUENCE OF MUSCLE-FIBER SIZE AND TYPE DISTRIBUTION ON ELECTROMYOGRAPHIC MEASURES OF BACK MUSCLE FATIGABILITY

Citation
Af. Mannion et al., THE INFLUENCE OF MUSCLE-FIBER SIZE AND TYPE DISTRIBUTION ON ELECTROMYOGRAPHIC MEASURES OF BACK MUSCLE FATIGABILITY, Spine (Philadelphia, Pa. 1976), 23(5), 1998, pp. 576-584
Citations number
46
Categorie Soggetti
Orthopedics,"Clinical Neurology
ISSN journal
03622436
Volume
23
Issue
5
Year of publication
1998
Pages
576 - 584
Database
ISI
SICI code
0362-2436(1998)23:5<576:TIOMSA>2.0.ZU;2-E
Abstract
Study Design. This was a cross-sectional study carried out on a group of 31 healthy, consenting volunteers with no history of low back pain (17 men, 14 women). Objectives. To evaluate the relationship between e lectromyographic measures of erector spinae fatigability and the muscl e's fiber type characteristics. Summary of Background Data. Using elec tromyographic techniques, a pronounced fatigability of the muscles of patients with low back pain has been identified. It has been postulate d that this is the result of an unfavorable back muscle fiber type dis tribution, although an association between electromyographic measures of fatigue and the muscle's fiber type characteristics has never been established. Methods. Two tests of back extensor fatigability were per formed (on separate days), each to the limit of endurance: 1) maintena nce of 60% total maximum voluntary contraction of the back extensors, and 2) performance of the Biering-Sorensen test. Pairs of surface elec trodes were attached to the skin overlying the belly of the erector sp inae, bilaterally, at T10 and L3. The median frequency was computed fo rm the electromyographic power spectrum, and fatigability was given by the slope of the linear regression of median frequency on time (MFgra d; %.s(-1)). One week later, two percutaneous erector spinae muscle bi opsy samples were obtained from the same sites described for electromy ography (left side only). Samples were prepared for histochemistry for the identification of muscle fiber types. Fiber sizes (cross-sectiona l areas) were quantified using computerized image analysis. Results. T he mean fiber size at each erector spinae region showed a significant correlation with maximum back extensor strength. In the thoracic regio n, the relative area of the muscle occupied by Type I fibers (which ac counts for the relative size and distribution of the fiber types) show ed a significant relationship with MF-grad recorded during each fatigu e test. A similar relationship was observed for the lumbar region, but for the Biering-Sorensen test only. Conclusions. The electromyographi c changes recorded in back muscles during fatigue appear to be related to the underlying muscle fiber type area distribution. This confirms the usefulness of electromyography in reflecting such muscle character istics in a noninvasive manner, when monitoring changes in function co nsequent to the development of, or rehabilitation from, low back pain.