Serum creatine kinase and isoenzyme responses of veteran class fell runners

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Abstract
The exercise response of creatine kinase (CK) and creatine kinase MB (CK-MB) was studied in 11 veteran class male fell runners (aged >40 years) following (1) a laboratory functional diagnostic test (GXT) to maximum oxygen uptake (VO2 max), (2) a competitive fell race (8 km distance and 419 m total height gain) at approx. 80% VO2 max. 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 (x 2.0 U·1−1, pp−1. Post-fell race CK-MB rose significantly (x 2.4 U·1−1, pp−1 (p−1). An inverse relationship was observed between MB/CK% and time to complete the fell race. It is probable 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.