Elevated serum creatine kinase MB and creatine kinase BB-isoenzyme fractions after ultra-marathon running.

To determine the incidence and range of serum creatine kinase MB (CK-MB) isoenzyme activity after ultra-marathon running, a popular test kit was used to measure total serum creatine kinase (CK) and CK MB-activity in 75 athletes immediately after they had completed an 88-km running race. Total serum CK activity was markedly elevated after the race (mean value: 637 U X 1(-1) and 45 (60%) runners showed abnormal CK-MB isoenzyme activities (greater than 4% of total CK activity - range 1-19%). Electrophoresis of 31 sera with either CK-MB to total CK activity greater than 4% or with total CK activity greater than 854 U X 1(-1) showed that 31 (100%) had visible CK-MM bands, 21 (68%) had visible CK-BB bands, but only 14 (44%) had visible CK-MB bands. We conclude that prolonged exercise increases the serum activity of all three CK-isoenzymes, and that the CK-MB test kit used in this study identified a greater number of sera with elevated post-race CK-MB isoenzyme activity than did electrophoresis. This discrepancy could result either from cross-reaction of elevated CK-BB activity with the test kit, or from relative insensitivity of the electrophoresis. The tissue source and long-term significance of the elevated serum CK-MB and CK-BB isoenzyme activity induced by ultra-marathon running are uncertain. Until these issues are resolved, these biochemical findings in ultra-marathon runners must be interpreted with the appropriate caution.