Power spectrum analyses of electromyographic activity. Discriminators in the differential assessment of patients with chronic low-back pain.

Some parameters of the electromyographic power spectrum of the paraspinal muscles were recorded and analyzed with regard to their ability to discriminate between normal controls and patients with back pain classified as "avoiders" or "confronters" by their responses to the Pain Behavior Checklist. In terms of the activity of the multifidus muscle, the avoider group displayed spectral changes towards lower frequencies, reduced variability in the density spectrum, and higher values of estimated initial frequencies. Measures of the activity of the iliocostalis lumborum did not contribute in any significant way to these group differences. Based on these findings, and on the available literature concerning the histology and physiology of paraspinal muscles, it is proposed that the observed characteristics of the avoider group may be due to a reduced ratio of slow twitch to fast twitch muscle fibers in the multifidus.