Electromyographic study of muscle fatigue on patients with chronic low back pain

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Electromyographic study of muscle fatigue on patients with chronic low back pain


Author: Lam, Frederick T. F
Title: Electromyographic study of muscle fatigue on patients with chronic low back pain
Degree: M.Phil.
Year: 2001
Subject: Backache -- Patients -- Rehabilitation
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Rehabilitation Sciences
Pages: viii, 131 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1578445
URI: http://theses.lib.polyu.edu.hk/handle/200/1019
Abstract: Endurance of the muscles on the back is considered as an important contributing factor in the development of low back pain (LBP). Currently, researchers are looking at reliable methods for measuring back muscles' fatigue rate by surface electromyogram (EMG). Many of these studies are still at the experimental stage and the feasibility of using EMG as a clinical tool for such purpose remains uncertain. This study attempted to monitor and quantify muscular endurance of the back through the measurement of surface EMG. Comparison has been made between the fatigue rate of a group of able-bodied subjects and another group of gender-, age-, weight- and height-matched patients with chronic low back pain (CLBP). Twenty patients with CLBP (mean age (yr)=33.15, S.D.=6.06) and 20 able-bodied subjects (mean age (yr)=32.65, S.D.=5.41) participated in this study. The average duration of LBP for the patients with CLBP was 2.15 years (S.D.=l .57). Two pairs of surface electrodes were placed along the muscle fibres of the two back extensors i.e., the iliocostalis lumborum and multifidus. The subjects were positioned in prone lying with their upper trunk maintained in an unsupported horizontal position for 30 seconds (Sorenson's test) while EMG were picked up from these two muscles. In order to observe the recovery of muscle fatigue, the procedure was repeated after a rest of 60 seconds. The EMG parameters chosen included the root-mean-square slope (RMS slope), initial root-mean-square voltage (Initial RMS voltage), median frequency slope (MF slope) and initial median frequency (Initial MF). A positive RMS slope was found on both able-bodied subjects and patients. This could be explained by additional recruitment of motor units during sustained contractions of the back muscles. However, there was no significant difference found in the initial RMS voltage and RMS slopes between able-bodied subjects and patients. It is therefore not possible to use RMS parameters alone to differentiate the difference in endurance of the back muscles between these two groups of subjects. The MF was relatively less variable than RMS voltage. A negative MF slope was found on both able-bodied subjects and patients with CLBP. This could be explained by accumulation of metabolite, leading to a decrease in the conduction velocity of motor units during fatiguing contraction. This was particularly noticeable on patients with CLBP. A steeper mean normalised MF slope (p<0.05) for iliocostalis lumborum was found on patients (-0.73 %/s(+-0.26)) when compared with able-bodied subjects (-0.51 %/s(+-0.19)). This indicated a poorer muscular endurance of this muscle on patients with CLBP, which could imply a smaller percentage of type 1 muscle fibres. The results did not show any correlation between the physical characteristics of the subjects and the MF. This may be due to similar variability of the physical measurements in both groups of subjects. There was no significant difference in the initial MF between these two groups of subjects. In addition, it was found that both MF and RMS parameters recovered back to their normal values after 60s. The subjects may therefore be regarded as sustaining a low load of fatiguing contraction during the Sorenson's test. In summary, this study established a protocol of MF measurement which could be useful for further investigation of its use as a discriminative variable between able-bodied subjects and CLBP patients. Longitudinal monitoring of the fatigue rate and hence endurance of the back muscles could also be established in a clinical setting.

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