Between-days reliability of subjective and objective assessments of back extensor muscle fatigue in subjects without lower-back pain

Background: It is important to evaluate the reliability of common used meth ods of examining muscle fatigue from the lower back since the methods are u sed in patient evaluation. Methods: To establish between-days reliability, ten subjects without lower- back pain performed a Sorensen test, a prone test for back extensor muscles against gravity, on three separate days. EMG was recorded from the L1 and L5 of the back extensor muscles. Fatigue was subjectively rated using a Bor g CR-10 scale. Intraclass correlation coefficient, standard error of measur ement and coefficient of variation were calculated from a one-way ANOVA. Pe rcent agreement was also calculated. Results: The study revealed good reliability for the slope for the total ti me (ICC 0.65-0.90), the initial and end median frequency (ICC 0.75-0.89), m edian frequencies at Borg ratings of three (ICC 0.63-0.88), five (ICC 0.62- 0.84) and seven (ICC 0.67-0.87), endurance time (ICC 0.89). The Borg rating s of the first minute agreed better than those of the second and the third. The Borg ratings at the second and the third test agreed to 40-80%, indica ting a need for a practice session. Conclusion: The protocol used for assessing fatigue in the back extensor mu scles proved to be reliable and is recommended for further use. (C) 2000 El sevier Science Ltd. All rights reserved.