Van Tulder, M., Becker, A., Bekkering, T., Breen, A., del Real, M.T., Hutchinson, A., Koes, B., Lærum, E., Malmivara, A. (2006). Chapter 3. European guidelines for the management of acute nonspecific low back pain in primary care. Eur Spine J. 2006 Mar;15 Suppl 2:S169-91.