Surface EMG in chronic low back pain.

Chronic low back pain (CHLBP) occupies first place among factors restricting people's life activity under the age of 45. Frequency of CHLBP occurrence oscillates between 60 and 80%. Dysfunction of the erector trunci is a fundamental cause of CHLBP. The aim of the study was to evaluate the usefulness of surface electromyography (EMG) as an identification method in CHLBP. EMG apparatus was connected to a PC equipped with the EMG-LAB programme. This programme allows the registration, transformation, analysis and projection of results on-line. A summary of complete examination is presented in the form of statistical values of parameters such as mean amplitude, mean density, background amplitude, background density, and upper amplitude and upper density. Plain, surface electrodes were attached to the skin overlying the erector spinae at the T7 and L4 vertebrae, approximately 3-4 cm from the midline of the back. Electrodes were positioned unilaterally on the right side. A reference electrode was positioned on the skin overlying the right arm. Sixty-two patients with CHLBP were examined (30 men and 32 women, mean age 41 +/- 8 years). The control group consisted of 31 people without back problems (16 men and 15 women, mean age 39 +/- 6 years). The statistical values of mean amplitude, mean density and upper amplitude were found to be higher in the control group at the T7 level. At the L4 level, mean amplitude, mean density, background amplitude, background density and upper amplitude were significantly higher in control group. The findings of this study show that (1) dysfunction of the erector spinae plays a significant role in CHLBP, and (2) this process applies to small and large motor units, but the character of these changes is different in particular muscles. Surface EMG is an objective, non-invasive method of examining function of the erector spinae in the author's opinion.