Creatine kinase MB and citrate synthase in type I and type II muscle fibres in trained and untrained men

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Abstract
Total creatine kinase (CK), creatine kinase MB (CK-MB) and citrate synthase (CS) were determined in isolated and pooled type I and type II skeletal muscle fibres. Determinations were made on biopsies from 3 sedentary men, 3 junior cyclists and 2 elite cyclists. CS and CK-MB activities were higher in the trained groups in both fibre types. The total CK activity was not related to training status, although it was lower in type I fibres than in type II fibres (ppp<0.01). Thus, with endurance training there seems to be a specific adaptation for CK-MB, particularly in type I fibres.