Heck, J. F., & Sparano, J. M. (2000). A classification system for the assessment of lumbar pain in athletes. Journal of athletic training, 35(2), S. 204-211. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1323419/?page=1

Heck, Jonathan F., and Jeana M. Sparano. "A Classification System for the Assessment of Lumbar Pain in Athletes." Journal of Athletic Training 35, no. 2 (2000): S. 204-211.

Heck, Jonathan F., and Jeana M. Sparano. "A Classification System for the Assessment of Lumbar Pain in Athletes." Journal of Athletic Training 35.2 (2000): S. 204-211.