Pain alters muscles' response to perturbation

[Guest guest]

April 2007 Biomechanics Magazine

Pain alters muscles' response to perturbation

By: Jordana Bieze

http://www.biomech.com/showArticle.jhtml?articleID=198900169

Trunk muscles in patients with low back pain exhibit impaired

responses to perturbation that could contribute to decreased

postural stability, according to two separate studies presented in

February at the APTA's annual Combined Sections Meeting.

In an 82-subject study, researchers from Drexel University in

Philadelphia, PA, found that low back pain was associated with

significantly delayed onset of several trunk muscles and

significantly fewer muscles activated in a feed-forward manner in

response to a self-generated upper extremity perturbation. In the 43

subjects with low back pain, delay in onset ranged from 75 to 99 ms

and occurred in the internal oblique and erector spinae muscles on

the ipsilateral side and in the external oblique, rectus abdominus,

and lumbar multifidus on the contralateral side. In those with back

pain, a mean of 4.1 muscles were activated in a feed-forward manner,

compared with 5.3 in the asymptomatic group.

Meanwhile, researchers from Ohio State University also found

significant differences between subjects with and without back pain

in response to an external perturbation. In four asymptomatic

subjects, a 100-N impulse force elicited a lumbar multifidus

response within 30 ms or less, typically followed by erector spinae

response; the extensor muscle response then gave way to response

from the internal and external oblique muscles within 31 to 80 ms of

the perturbation. In two subjects with low back pain, however, the

researchers detected no initial multifidus activity, instead

measuring periods of flexor-extensor cocontraction beginning about

30 ms after the perturbation.

The results of both studies suggest that neuromuscular training may

help improve postural stability in low back pain patients.