Electrocardiographic and biochemical studies on marathon runners.

The electrocardiographic findings and certain biochemical observations in 48 male runners before and after participation in the Comrades Marathon race are presented. In 21 of the 48 runners electrocardiographic changes consistent with early ischaemic heart disease could be demonstrated before the race. In 2 runners who had normal tracings before the race, abnormalities could be shown after the race. The total serum creatine kinase activity was markedly elevated after the race in the majority of the 23 runners in whom this was measured. In 11 of these subjects, the Marsh-Bender (MB) fraction could be demonstrated after the race. It is concluded that an elevated MB fraction is probably not a reliable index of myocardial damage after strenuous exercise.