Background: To evaluate the effect of continuous, moderate-intensity ultra-endurance running exercise on skeletal muscle and hepatic damage, as indicated by serum enzyme activity measured immediately following the race.
Methods: Thirty-nine runners of the Spartathlon race (a 246-km continuous race from Athens to Sparta, Greece) who managed to complete the race within the 36-h limit participated in this study. Mean finishing time of the study participants was 33.3+/-0.5 h and their average age, height, and body mass were 41+/-1 yr, 174+/-1 cm, and 67.5+/-1.1 kg, respectively. Blood samples, taken a day before and immediately after completion of the race, were assayed for the following variables: creatine kinase (CK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyltransferase (gamma-GT).
Results: A dramatic increase in most of muscle and liver damage indicators was observed. The mean values for CK, LDH, AST, and ALT after the race were 43,763+/-6,764, 2,300+/-285, 1,182+/-165, and 264+/-37 IU.L, respectively. These values were 29,384+/-4,327, 585+/-89, 5,615+/-902, and 1,606+/-331% higher than the corresponding values before the race (P<0.001) for CK, LDH, AST, and ALT, respectively. However, there was not a significant increase in gamma-GT levels.
Conclusion: Muscle and liver damage indicators were elevated at the highest level ever reported as a result of prolonged exercise, although no severe symptoms that required hospitalization were observed in any of the participants. The data suggest that even moderate-intensity exercise of prolonged duration can induce asymptomatic exertional rhabdomyolysis.