Diagnostic accuracy and reliability of muscle strength and endurance measurements in patients with chronic low back pain.

OBJECTIVE Dynamometric trunk muscle strength and endurance tests are performed widely within the rehabilitation management of chronic low back pain. The aim of this study was to examine the accuracy and long-term reliability of these measurements in patients with chronic low back pain. DESIGN Cross-sectional study. SUBJECTS Thirty-two patients with chronic low back pain, 19 healthy controls and 15 patients with chronic headache matched for age, sex and body mass index. METHODS Both patient groups and healthy controls performed isokinetic and isometric trunk extensor and flexor tests on a Biodex 2000 dynamometer. The Biering-Sørensen test served to examine back muscle endurance. Borg-Category-Ratio-Scales CR-10 rated participants' body experience immediately before and after the testing. Patients with chronic low back pain repeated measurements after 3 weeks. RESULTS Among dynamometric tests, isokinetic measurements revealed the best area under the curve (AUC = 0.89) for the discrimination between patients with chronic low back pain and healthy controls. Reliability testing revealed highly significant learning effects for isometric trunk flexion and isokinetic measurements. The Biering-Sørensen test demonstrated excellent accuracy (AUC = 0.93) and no learning effects. Borg-category-ratio-scale ratings were not associated with the observed changes. CONCLUSION In chronic low back pain dynamometric trunk muscle measures are limited to muscle function assessment purposes. Monitoring treatment outcome in these patients with these measures appears to be problematic because of learning effects. Based on our findings, we recommend the Biering-Sørensen test for management of chronic low back pain rehabilitation.