Reference change limits of the paraspinal spectral EMG in evaluation of low back pain rehabilitation
Introduction
Poor back extensor muscle endurance is common among chronic low back pain patients (CLBP) 1, 2, 3, 4, 5and CLBP is accompanied with type II fibre atrophy in multifidus muscles [6]. These changes are reversible with back muscle training 2, 7, 8. Paraspinal muscle fatigue results for abnormal trunk movements and loss of muscle control which may lead to microinjury of ligaments and intervertebral discs 9, 10, 11. Also, excessive paraspinal fatigability represents a risk for future low back pain 5, 12, 13. Therefore, back muscle endurance plays a vital role in the assessment of lumbar spinal function and dysfunction.
Active rehabilitation is widely used in the treatment of chronic low back pain, but it is not known how much and to whom this should be prescribed [14]. This is partly due to the lack of objective physiologic measurement that would quantify the program outcome and treatment efficacy. In clinical practice, back extensor strength and maximal endurance are used, although subject motivation and current level of pain influence the result. Lumbar paraspinal EMG spectral compression towards lower frequencies is used to measure the back extensor muscle fatigability in isometric test conditions 1, 2, 5, 15, 16and applied for the follow-up of active rehabilitation 2, 15, 17.
The endurance tests that are used in back muscle testing may involve other muscle groups, e.g. hip extensor muscles [18]. Submaximal isoinertial back endurance test using spectral EMG has been evaluated for its validity to assess the lumbar back muscle fatigability [19]. In this test, the subject is seated on a test device that targets the loading to the lumbar paraspinal muscles and restricts the use of the hip extensor muscles. The level of loading is calculated on the basis of subject upper body mass, and therefore no maximal voluntary back extension force measurements are needed. Similar dynamic testing conditions using EMG spectral compression have been used in the assessment of paraspinal muscle fatigability 17, 20, 21.
One goal in active low back rehabilitation is to improve the paraspinal muscle endurance. It is assumed that the recently developed isoinertial back endurance test using spectral EMG would be suitable for objective assessment of improved back muscle endurance during the active low back rehabilitation. Before using that for the rehabilitation follow up, one must determine the responsiveness of the EMG method. This can be done by assessing the reference change limits (RCL) of the variable. The RCL is a minimal threshold limit that should be exceeded in order to achieve significant change in a variable 22, 23.
The aim of the present study was to assess the RCL of isoinertial back endurance test with EMG spectral mean power frequency compression as a measure of paraspinal muscle fatigability, and to evaluate how the back extensor muscle endurance changes during the active back rehabilitation.
Section snippets
Subjects
This study was approved by Kuopio University Hospital Human Ethics Committee (Kuopio, Finland). Fourteen females (age 44.9±7.6 years, height 164.1±5.8 cm, weight 63.4±7.9 kg) were recruited from the employees of North Karelia Central Hospital and Kuntohovi Rehabilitation Centre (Joensuu, Finland) to participate in the study examining RCL of the repeated measures. After signing a written voluntary consent, the subjects were clinically examined in order to exclude the specific low back disorders.
RCL in repeated measurement assessments
The correlation between the repeated measurements of MPFSLOPE on the left and right side of the spine, and for their pooled data was 0.89–0.94 (P<0.001, Fig. 2). The RCL of the pooled MPFSLOPE with 90% confidence interval was 4.5% decrease·min−1 change for the improved result (positive outcome) and −3.4% decrease·min−1 change for the impaired result (negative outcome).
Changes in pain and disability
Both low back pain intensity (VAS) and functional disability (OSW) improved during the rehabilitation (P<0.05). The estimates of
Discussion
We assessed the reference change limits for the paraspinal muscle EMG spectral decrease obtained during the submaximal isoinertial trunk extensor endurance test. Eight chronic low back pain patients out of 15 improved, two became worse and five did not show significant changes in their EMG spectral compression after 10-week active rehabilitation. It is thus possible to define the individual improvement level in order to consider the result to be due to intervention rather than intraindividual
Conclusions
It was possible to define the reference change limits for the spectral EMG obtained during the submaximal isoinertial back endurance task. According to this, active rehabilitation program was only moderately effective on improving the lumbar paraspinal muscle endurance when the individual test results were considered. The changes in back pain intensity were moderate to good and functional capacity changed only marginally. The close relationship between the spectral EMG measurements in
Acknowledgements
The Finnish Ministry of Education and Finnish Academy (TULES Graduate School), Finnish Work Environmental Fund, The Finnish Medical Society Duodecim, and Yrjö Jahnsson, Eemil Aaltonen and Instrumentarium Science Foundations supported the study. We would like to acknowledge Pirjo Halonen, MSc, Satu-Mari Kokko, MSc, Sirpa Moilanen, Pt. and Timo Piironen, Pt. for their valuable help. We would also like to thank the doctors of the Kuopio Occupational Health Center for their help in recruiting the
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