Heck, J. F. (1996). The incidence of spearing during a high school's 1975 and 1990 football seasons. Journal of athletic training, 31(1), S. 31-37. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1318352/pdf/jathtrain00017-0033.pdf

Heck, Jonathan F. "The Incidence of Spearing During a High School's 1975 and 1990 Football Seasons." Journal of Athletic Training 31, no. 1 (1996): S. 31-37.

Heck, Jonathan F. "The Incidence of Spearing During a High School's 1975 and 1990 Football Seasons." Journal of Athletic Training 31.1 (1996): S. 31-37.