Harden, L.; Neveling, N.; Rossouw, F.; Semple, S.; Marx, F.; Rossouw, J.; Rogers, G. 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. SA J Sports Med 2004, 16, 10-16.