[Muscle cell proteins are selectively released into the blood stream by marathon running]

In 19 marathon runners of both sexes, plasma concentrations of total creatine kinase (CK) activity, CKMB mass, myoglobin and troponin I were determined before and immediately after the race. Total CK activity and myoglobin increased significantly in all runners and showed neither a correlation with the individual age of the runners nor with the time they needed to reach the goal. In 12 of the runners, CKMB mass increased during the race to a level suggesting myocardial necrosis. However, the runners did not show any detectable deterioration of cardiac function after the race. The appearance of considerable amounts of muscle proteins in plasma precipitated by the muscle strain during the race seems explained by damage of skeletal muscle detected by histological studies. These phenomena may also be a consequence of profoundly disturbed cellular permeability, perhaps due to a kind of local stunning of muscle tissue by prolonged muscular strain.