Classification of back muscle impairment based on the surface electromyographic signal.

A surface electromyographic (EMG) procedure for classifying muscle impairments in persons with low back pain (LBP) is described. The procedure was studied using a device, the Back Analysis System (BAS), to acquire and process EMG signals from six bilateral muscle sites during sustained isometric contractions designed to progressively fatigue the lower back. Back muscle impairment was determined on the basis of the different ways in which the EMG median frequency parameters change as a function of contraction duration and muscle site. The article describes a series of studies that have been useful in developing an automated procedure for identifying back muscle impairment by comparing individual test results to a normative database. To date, the research results have produced multivariate discriminant functions that have identified two muscle impairment categories associated with deconditioning and imbalances secondary to LBP. We have found that the functions can distinguish individuals with and without LBP with an accuracy of approximately 90%. Other studies are described in which the technique is applied to monitoring changes in muscle performance capability that occur following rehabilitation for LBP. Many of our findings here are also compared to the results of independent studies by others using similar procedures. The need for further research and development of the technique to improve its clinical applicability is also described.