Creatine Kinase Levels After Exercise

Physical exercise or strenuous sporting activities can increase blood creatine kinase (CK) levels—something to bear in mind in patients with suspected statin-associated muscle symptoms. In their article about CK increases under statin treatment, Laufs et al. have repeatedly highlighted this important aspect (1). Nevertheless, some comments are necessary to supplement the information provided.

Muscle exercise stress does not regularly “increase CK levels to 500–600 U/L“ (1); in this respect, there is considerable interindividual variability. The majority of competitive athletes have raised CK level in the blood (2). In individual cases, CK levels may occur that are clearly above 1000 U/L (3). However, some athletes show only moderate or no response (non-responders) (4). Regular preventative exercise with relatively constant muscular-mechanical stress is not often associated with CK increases. On the other hand, CK levels respond to marked changes in the amount and intensity of exercise. Thus, CK levels may increase significantly after unusual and eccentric types of exercise. This primarily applies to strength and speed-strength exercise stress (4). Therefore, taking a thorough exercise history is important to resolve issues with differential diagnosis. A cut-off CK concentration of more than 4x upper limit of normal (ULN) is of little diagnostic value. One can only agree with the authors that patients with suspected exercise-induced CK increases should observe a training break of one week. Unfortunately, competitive athletes often find it quite impossible to do this.

Marked increases in CK activity in the blood are often associated with an increase in aminotransferases; here, glutamic oxaloacetic transaminase (GOT)/aspartate aminotransferase (AST)—because of its higher muscular activity—shows a stronger response compared with glutamic pyruvate transaminase (GPT)/alanine aminotransferase (ALT). Gamma-glutamyl transpeptidase (GGT) remains unchanged (3). Increases in aminotransferase levels can be expected when the creatine kinase levels exceed 3x-4x ULN.