For well over a decade my associates and I have been developing an objective, noninvasive technique to evaluate the performance of low-back muscles, with emphasis on being able to distinguish between healthy and dysfunctioned backs. Our approach is based on the well-known fact that the EMG signal undergoes a compression in the frequency domain during a sustained muscle contraction. In particular we track the median frequency of EMG signals detected from six muscles in the lower back during an isometric extension of the trunk. The measurements are taken with the Back Analysis System which consists of a postural restraining device, special electrodes for detecting the EMG signals, a muscle fatigue monitor which calculates the median frequencies, and the appropriate software. We have found that the pattern of fatigue exhibited by the six median frequency curves can be used to distinguish individuals who have low-back pain from those who do not with an accuracy of at least 84%. An even more relevant and timely application of our technique is for quantifying the progression of the performance of low-back muscles during a rehabilitation program. Although more work is required to explore the intricacies of the technique, present results provide a convincing indication that it is reliable and that it is ready to be placed into practice.