Creatine kinase and hexose phosphate isomerase activity in skeletal muscles of healthy male adults.

Creatine kinase (CPK) and hexose phosphate isomerase (PHI) activities were measured in surgically obtained skeletal muscle samples of healthy adult men (n = 45). Median values of 4,200 for CPK and 275 for PHI (U/g wet weight, 37 degrees C) were found. Duplicate determinations on 7 samples divided and treated separately gave a very good reproducibility. There is a significant relationship between the activity of the two enzymes (r = +0.798, p less than 0.001). The mean activity levels were for both enzymes higher in m. vastus medialis quadricipitis and m. triceps brachii, c. long., than in vastus lateralis quadric. and in deltoideus. PHI frequency distribution was not of the normal type but probably bimodal, suggesting muscle types with lower and higher glycolytic rate in man.