What causes creatinine kinase levels to rise with muscle weakness?

Damage to muscle. The correct term is creatine kinase (ck). Creatinine is something else. Useful to know: most "muscle" weakness is actually caused by nerve, not muscle, malfunction. True muscle weakess: myocytes (muscle cells) contain lots of the enzyme ck. Low levels are found in blood normally. Damage to myocyte cell membranes from a variety of causes causes leakage of ck into the blood. Recovery->normalization.
Muscle damage. Damage to muscle (including heart)tissue, causes the release of creatinine kinase into the blood stream. The damaged muscle is weaker as a result. The creatinine kinase (CPK) levels are increased in a heart attack, muscle injury/inflammation, or due to taking statin medications. Talk to your doctor for clarification.