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EMG-based classification of low back pain
February 2003
| Principal Investigator: | Ted Milner, Simon Fraser University |
For more information about this study, please contact Dr. Milner.
Issue
With the high incidence and associated cost of work-related low back pain (LBP), an accurate, objective and safe method is needed to assess lumbar impairment. With LBP, the ability of paraspinal muscles to resist fatigue is reduced, and the reactive response of trunk muscles is delayed. A method for classifying LBP based on these impairments was developed and assessed for accuracy.Key findings
- Results indicate that assessment of reactive responses of trunk muscles produced a more accurate method for classifying LBP than measures of fatigue. Using average muscle reaction times, a model was developed that was able to accurately classify individuals with and without LBP.
- Because the reaction times measured during the study indicate that the responses were reflexive in nature and not voluntary, it appears that the protocol is objective and cannot be affected by motivational issues or fear of injury.
- Due to the small magnitude of perturbation force and displacement generated during testing, the protocol also appears to be a safe method for classifying LBP.
Objectives
- To determine if measures of fatigue and reactive responses of trunk muscles could accurately classify individuals with and without LBP
- To develop and validate an assessment tool for classifying LBP based on these measures.
Method
Sixty people in total participated in the study of which 31 were LBP patients and 29 were healthy controls.
Subjects were placed in a semi-seated position in a testing apparatus which allowed isometric contraction in trunk flexion, extension and lateral bending to the left and right. This apparatus was designed to restrain hip motion while allowing the upper body to move freely in any direction, so that response patterns of trunk muscles were responsible for all postural readjustments.
Isometric force was applied through a cable attached to a chest harness at approximately T9 and was held with an electromagnet. The quick release of this electromagnet produced the sudden unloading on the trunk, resulting in displacement of the trunk, and initiating reactive responses in the trunk muscles.
Changes in the electrical signal recorded from muscles during isometric contraction and individual muscle reaction times in response to trunk displacement were recorded. A logistic regression model was developed using these measures to distinguish individuals with and without LBP.
Results
In general, individuals with LBP tended to have longer muscle reaction times and more variability than healthy controls. There was no significant difference in parameters related to muscle fatigue between individuals with and without low back pain at 60% of maximum isometric force.
Conclusions
The primary goal of the study was to determine if differences in muscle fatigue and/or reaction latency to unexpected trunk displacement could accurately classify individuals with and without LBP. From the results of this study, muscle reaction time following load-release appears to be an accurate method of classifying LBP, and provides further evidence to suggest that individuals with LBP have altered recruitment of trunk muscles.
Future directions
Future research may allow for clinical applications of this reaction classification model for LBP, such as in the objective assessment of impairment and evaluation of LBP treatment options.
Publications
Reeves, N.P., Cholewicki, J. and Milner, T.E. (2005) Muscle reflex classification of low-back pain. J. Electromyogr. Kinesiol. 15: 53-60
Reeves, N.P., Cholewicki, J. and Milner, T.E. (2004) Muscle reaction classification of low back pain. ISEK 2004