Exercise initiates several changes in the body and its physiology which can help improve your performance. Ironically, the improvements in your body's efficiency occur as the result of muscular damage caused by exercise. While some changes such as increased muscle mass are evident, other changes occur in the body's chemistry. One chemical is an enzyme linked with energy production called CPK.
The Role of CPK
CPK or creatine phosphokinase is an enzyme of the body that is found within the skeletal muscles as well as in the heart and brain. Enzymes are chemical structures that speed up metabolic reactions in the body. CPK helps your muscles produce energy when it is broken down into creatine phosphate, an important substrate used for ATP production during physical activity. ATP is the energy currency of the body. It is required by all cells of the body for normal functioning.
CPK and Muscle Response
Your blood concentration of CPK varies with physical activity. Very intense exercise can cause tears in your muscle fibers which your body subsequently repairs. The basic process involved in muscle adaptations to exercise involves the release of CPK in response to muscle damage. Levels may also rise with other forms of damage such as injuries from contact sports or a heart attack. Extreme damage to muscles can cause dangerous levels of CPK to leak into the bloodstream, leading to kidney damage or failure, a condition called rhabdomyolysis.
Endurance Exercise and CPK
Aerobic endurance exercise can result in elevated blood levels of CPK. A 2002 study published in the "Journal of Applied Physiology" found that after 90 minutes of cycling, subjects showed significantly elevated CPK levels three hours post exercise. Researches attributed the rise to properties of the quadriceps muscles. In a 2012 review article published in the "Journal of Nutrition and Metabolism, elevated creatine kinase levels after mild to moderate intensity aerobic exercise were due to a disturbance to muscle energy processes, and did not represent the severe damages characteristic of a heart attack or physical damage to the muscles.
When to Test CPK Levels
CPK levels are measured by a simple blood test. Post-exercise values can be elevated, and the test should not be taken after a vigorous exercise session. This test is typically run to diagnose a heart attack or diagnose chest pain rather than as a routine test. However, severe muscle pain, swelling and dark brown urine after exercise could indicate rhabdomyolysis, a life-threatening condition that calls for immediate testing and treatment.