Median frequency estimates of paraspinal muscles: reliability analysis.

The technique of monitoring the frequency shift of the electromyographic signal through a single parameter, the median frequency (MF), was investigated with regard to its reliability characteristics as tested on two back muscle groups: the multifidus and iliocostalis lumborum. The proportion of variance in the MF parameters accounted for by the test/retest reliability as well as by the left versus right side analysis is satisfactory for the multifidus, it is, however, consistently lower for the iliocostalis. For the purpose of measuring muscular function, the MF recording technique appears to be well suited for clinical research, its application in the assessment of muscular dysfunction of back muscles is nevertheless far from simple.