The creatine phosphokinase (CPK or CK) is a muscle enzyme test that is elevated any time there is any muscle injury. In the case of strenuous exercise, the elevation depends on how strenuous the exercise and the muscles injured. Each person is unique, so there is likely no way to predict how long it takes to normalize the muscle test. Hydration will prevent kidney injury from occurring. Marked injury to the muscle with “rhabdomyolysis” will cause red urine and could cause kidney injury. The elevation of CK tests is never normal but may be an expected finding in people who regularly engage in strenuous physical activity.