Creatine phosphokinase and lactate dehydrogenase levels after ultra long-distance running. An analysis of iso-enzyme profiles with special reference to indicators of myocardial damage.

Blood samples obtained from 20 runners on completion or partial completion of a 160-km marathon were assayed for total serum creatine kinase (CK) and lactate dehydrogenase (LD), as well as for the respective iso-enzymes. Total CK was significantly elevated in all subjects, the mean value (2 243 U/l) constituting a 24-fold increase above the normal upper limit. In 65% of these cases, the cardiac-specific iso-enzyme of CK, MB, was present. The mean LD level (1 220 U/l) also exceeded the upper limit of normal significantly, 5 subjects presenting a 'flipped' LD pattern (LD1 greater than LD2). Three subjects exhibited the MB iso-enzyme in the presence of a flipped LD pattern. No electrocardiographic evidence of irreversible cardiac 'damage' could, however, be established after the race, nor any significant decrease in the Bruce protocol stress test rating. It is concluded that the MB iso-enzyme of CK, even in conjunction with a flipped LD pattern, may not represent unequivocal evidence of myocardial damage under all circumstances.