Livingston, L. A., & Spaulding, S. J. (2002). OPTOTRAK measurement of the quadriceps angle using standardized foot positions. Journal of athletic training, 37(3), S. 252-255. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC164352/pdf/attr_37_03_0252.pdf

Livingston, Lori A., and Sandi J. Spaulding. "OPTOTRAK Measurement of the Quadriceps Angle Using Standardized Foot Positions." Journal of Athletic Training 37, no. 3 (2002): S. 252-255.

Livingston, Lori A., and Sandi J. Spaulding. "OPTOTRAK Measurement of the Quadriceps Angle Using Standardized Foot Positions." Journal of Athletic Training 37.3 (2002): S. 252-255.