# Creatine kinase (CK)

Creatine kinase (CK) is an enzyme that helps regenerate ATP energy, by moving a phosphate from phosphocreatine to ADP. It is busiest in tissues with high, fluctuating energy needs: your skeletal muscle, heart muscle, and brain. When those tissues are damaged, CK spills into your blood. Lab fractionation into isoenzymes helps pinpoint the source: CK-MM (skeletal muscle), CK-MB (heart), and CK-BB (brain). Historically, a CK-MB rise was used to diagnose a heart attack. But since the 2018 Fourth Universal Definition of MI, cardiac troponin (preferably high-sensitivity) has replaced it as the standard. A temporary CK spike after unusual hard exercise is normal and harmless. A persistent rise, though, suggests muscle disease (myopathy), severe breakdown (rhabdomyolysis), or statin-related muscle toxicity. In sarcopenia research, resting CK and its trend are explored as indirect signs of muscle-membrane integrity.

## Sources

- Brancaccio P, Maffulli N, Limongelli FM. (2007). Creatine kinase monitoring in sport medicine. British Medical Bulletin. https://doi.org/10.1093/bmb/ldm014

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