Harden, LM, N Neveling, F Rossouw, SJ Semple, FE Marx, J Rossouw, and G Rogers. 2004. “The Effects of an L-Methionine Combination Supplement on Symptoms of Upper Respiratory Tract Infections and Performance in Ultramarathon Runners Before, During and After Ultra-Endurance Exercise”. South African Journal of Sports Medicine 16 (1):10-16. https://doi.org/10.17159/2078-516X/2004/v16i1a188.