(en) In adult muscles, CPK activity is closely related to the concentration of CT. Following a powerful disturbance (i.e. slicing), this system remains tightly coupled and regenerates along a trajectory that first passes from a "slow muscle" type to a "fast muscle" type. The activity of the CPK or the concentration of CT may well therefore reflect the state of modulation of the muscle in differentiation. In the growing muscle however, the trajectory which carries the newborn towards the adult is different, the CPK growing faster, almost with the square of the CT. The adjustment of the mechanism that ensures the CPK-CT relationship of the growing muscle is therefore different from that of the adult muscle.
Maréchal, G., & Plaghki, L. (1979). [Cpk and Ct in Striated Muscles]. Archives Internationales de Physiologie et de Biochimie, 87(1), 141-142. (Original work published 1979)