A method to objectively assess muscular disorders of the lumbar back associated with chronic low back pain
Casavant, David A.
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Recent information regarding chronic low back pain indicates that approximately 80% of all cases are muscular in origin. However, presently available diagnostic techniques and prescribed treatments are often ineffective in detecting and remedying this common ailment. The research effort reported in this thesis involves an electromyographic techniques used to objectively evaluate abnormal back muscle interactions associated with low back pain. In order to measure the functional state of the trunk extensor muscles. myoelectric (ME) activity was monitored from multiple sites of the lumbar musculature during sustained, isometric contractions. The fatigue characteristics of each muscle were quantified by observing the spectral shift of the power spectrum of the ME signal. The resulting "fatigue patterns" thus represented the dynamic interaction of the synergistic back muscles. Differences in these patterns associated with low back disorders may represent functional disturbances. To obtain an indication of the force contribution of each muscle, their relative activity levels were also monitored. Multifactor analysis of variance (ANOVA) techniques demonstrated significantly higher fatigue rates in the back extensor muscles of back patients as compared to pain-free controls. With regard to overall strength, however, back patients and controls were remarkably similar. Possible explanations of the observed endurance deficiency in back patients are: 1) muscle atrophy resulting from low patient motivation and inactivity, or 2) higher precontraction metabolic concentrations in the erector spinae muscles of back patients caused by high resting tensions and frequent muscle spasm, or 3) compensation by healthy muscles in order to relieve and/or protect deficient and/or injured synergists. In conjunction with the above-described study involving back patients, additional research was performed using pain-free controls to investigate the ability of the erector spinae muscles to recover following a fatiguing contraction. Recovery was quantified by observing the time required for the ME power spectrum to return to it's initial state following fatigue. Preliminary findings suggest the existence a circulatory reactive mechanism occurring immediately following a high level, ischemia-producing contraction. Furthermore, the reproducability of the back assessment procedure was established by repeating the procedure on the same day and on adjacent days. The results maintained that the assessment procedure is reliable.
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