Muscle fatigue and lack of endurance are complaints of persons with chronic low back pain, but there are no standard ways to assess endurance in this population. The purposes of this study were to examine three measures of endurance, to determine relationships of these measures to each other, and to describe effects of gender, obesity, smoking, and self-reported fitness on the clinical measures. The measures of endurance selected were not dependent on maximal voluntary muscular contractions. They were the Sorensen test, median frequency decline of selected muscles, and a submaximal bicycle ergometer test. Thirty-five consenting individuals who were referred for treatment answered questions about their daily exercise prior to being tested. Repeatability of the Sorensen test holding time and of the slope measure of decline in the median frequencies was acceptable for subjects who reported a higher activity level. The decline of the median frequency in the biceps femoris muscles correlated with holding time of the Sorensen test. Smoking, gender, or obesity level did not affect test results on any of the endurance measures. Subjects who reportedly were more active achieved significantly higher scores on the Sorensen test. The importance of controlling for self-perception of activity in physical testing is discussed.
