Exercise & Creatine Kinase

Creatine kinase is an enzyme, or form of protein, that the body uses for quick energy. Normally, creatine kinase is confined to muscle cells. When damaged, the muscle cells may leak, allowing creatine kinase to enter the bloodstream. Elevated levels of creatine kinase in the blood can indicate an injury or disease, but it is also normal for many athletes to register higher levels after exercising.

Normal Creatine Kinase Levels

Doctors must evaluate many factors in determining what the normal creatine kinase level for each patient should be. Levels vary a great deal, depending on the patient's age, race and sex, as well as how much of his weight is muscle, his level of activity and even the climate. According to "The Journal of Family Practice," the normal, pre-exercise creatine kinase levels for males is between 55 and 170 units per liter, and the range is between 30 and 135 units per liter in females.

Exercises Elevating Creatine Kinase the Most

Creatine kinase levels can spike dramatically, but temporarily, after strenuous activities. Marathoners, triathletes, weightlifters and downhill runners are among those seeing the greatest elevations of the enzyme. "The Journal of Family Practice" reported that male marathoners showed a blood creatine kinase level that was more than 22 times greater than their normal prerace levels, and female marathoners had levels 8.6 times their prerace levels, a full 24 hours after the end of the race; triathletes had levels that averaged about 12 times pre-competition levels. In healthy patients, however, the creatine kinase levels soon declined as the muscles recovered from the exertion, returning to the levels that were normal and appropriate for each individual, based on his fitness level, age, gender and ethnicity.

Activities Providing Least Impact on Creatine Kinase Levels

Weight-bearing exercises cause the greatest increase in creatine kinase. Swimmers, cyclists and other engaged in non-weight-bearing activities saw only minor elevations in creatine kinase.

Timing of Elevated Creatine Kinase Levels

Creatine kinase levels are normally at their highest points 16 to 24 hours following the race or exercise session. After peaking, levels gradually decline and typically return to normal within approximately 72 hours.

Fitness Level and Creatine Kinase

Creatine kinase in the blood is an indication that the patient has experienced some degree of muscle damage. A person who has been exercising regularly for years and is in good physical condition will experience less muscle damage than someone who is new to exercise. Therefore, if an unfit person and one who is well trained participate in an identical exercise, the fitter participant should experience a lower rate of creatine kinase increase than the unfit participant. Because of this, doctors must evaluate the level of training and fitness of the patient in deciding whether creatine kinase levels are appropriately elevated.