Muscles are susceptible to damage, just like other body tissues. Trauma, infections, certain medications or even strenuous exercise can cause varying degrees of muscle injury. Pain is a common indicator of muscle damage but is generally not useful for establishing the extent of injury. For this reason, a biomarker in the bloodstream called creatine kinase is often measured to diagnose and evaluate muscle damage.
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Creatine Kinase Function
Creatine kinase, or CK, is a type of enzyme found within your muscles. It aids in the production of phosphocreatine, a molecule utilized by your muscles for energy. Injury to the membrane surrounding muscle cells allows CK to leak into the bloodstream.
CK exists as three forms: CK-MM, CK-MB and CK-BB. CK-MM is located primarily in the skeletal muscles, whereas CK-MB is localized to the heart and CK-BB is mostly found in the brain. For males over 18 years of age, normal blood CK levels typically range from 52 to 336 units per L, or U/L. Normal CK levels in females usually range from 38 to 176 U/L.
Causes of Elevated Creatine Kinase
Injuries to the skeletal muscles often trigger high levels of CK-MM. These muscles are the type that most commonly comes to mind when we hear the word muscle. They are "voluntary" muscles that you are able to control -- for example, your bicep and tricep. Damage to the skeletal muscles can occur for various reasons, including muscular dystrophy, trauma, strenuous exercise, immobility, certain drugs, muscle injections, seizures and surgery.
Strenuous exercise frequently triggers a rise in CK that peaks 16 to 24 hours following a workout, then stays elevated for 72 hours before falling back to baseline. Those with muscle diseases typically experience chronically elevated CK-MM. People with Duchenne muscular dystrophy may have CK-MM levels 50 times greater than normal.
Branched Chain Amino Acids
Some studies suggest that amino acids may ameliorate elevation of CK levels after exercise. According to a study published in December 2007 in the "International Journal of Sport Nutrition and Exercise Metabolism," branched-chain amino acid, or BCAA, supplements may reduce CK levels after exercise as well as muscle damage and soreness. The study researchers found that consumption of a beverage containing 200 kilocalories of BCAA immediately before and 60 minutes into a workout reduced CK levels 4, 24 and 48 hours after completion of exercise. These findings may be of benefit to people suffering from delayed onset muscle soreness after exercise.
One of the most common causes of elevated CK is a lack of oxygen to the heart muscle, known medically as a myocardial infarction or heart attack. CK-MB levels typically peak 2 to 24 hours following a heart attack and gradually fall back to baseline after three to four days. Seek immediate medical attention if you have symptoms of a heart attack, such as chest pain, shortness of breath, jaw pain that radiates to your left arm or excessive perspiration. Since many of the causes of skeletal muscle damage can also be quite serious, contact your doctor if you experience severe or prolonged muscle pain or weakness.
- Muscular Dystrophy Association; Simply Stated . . . The Creatine Kinase Test; February 2000
- MedlinePlus; CPK Isoenzymes Test; David C. Dugdale III, M.D.; February 2011
- International Journal of Sport Nutrition and Exercise Metabolism: Branched-Chain Amino Acid Supplementation and Indicators of Muscle Damage after Endurance Exercise
- ChronoLab: Creatine Kinase (CK) Clinical Significance