Serum creatine kinase and isoenzyme responses of veteran class fell runners

The exercise response of creatine kinase (CK) and creatine kinase MB (CK-MB) was studied in 11 veteran class male fell runners (aged greater than 40 years) following (1) a laboratory functional diagnostic test (GXT) to maximum oxygen uptake (VO2max), (2) a competitive fell race (8 km distance and 419 m total height gain) at approx. 80% VO2max. Subjects rested for 72 h pre- and 24 h post-GXT test, resuming normal training for 8 days before resting again 72 h pre- and 24 h post-fell race. Blood samples were obtained during normal training, pre- and 24 h post-GXT test, and pre-, 24 and 48 h post-fell race. Two distinct exercise profiles emerged. Post-GXT test CK-MB rose significantly (mean 2.0 U x 1(-1), p less than 0.05) with the mean values of per cent CK-MB to CK (MB/CK%) rising to 4.4% (p less than 0.01). Total CK remained stable at 50 U x 1(-1). Post-fell race CK-MB rose significantly (mean 2.4 U x 1(-1), p less than 0.01) with the mean MB/CK% rising to 3.1% (p less than 0.05) and total CK to 81.6 U x 1(-1) (p less than 0.01). Two subjects who exhibited ECG abnormalities during and post-GXT test, were observed to have the highest MB/CK% post-test (8.2 and 5.6% respectively) and the highest CK-MB (2.3 and 3.7 U x 1(-1). An inverse relationship was observed between MB/CK% and time to complete the fell race. It is probably that the increase in serum isoenzyme CK-MB following exercise arises from myocardial tissue efflux, reflecting reversible ischaemia. CK-MB appears to be a very specific indicator of myocardial stress during exercise.