Gruther, W., F. Wick, B. Paul, C. Leitner, M. Posch, M. Matzner, R. Crevenna, and G. Ebenbichler. “Diagnostic Accuracy and Reliability of Muscle Strength and Endurance Measurements in Patients With Chronic Low Back Pain”. Journal of Rehabilitation Medicine, vol. 41, no. 8, June 2009, pp. 613-9, doi:10.2340/16501977-0391.