The enzyme CPK is an indicator of damaged muscle fiber after intense exercise


February 08, 1994|By Dr. Gabe Mirkin | Dr. Gabe Mirkin,United Features Syndicate

The soreness that you feel on the day after you exercise intensely is caused by damage to the muscle fibers. Muscle biopsies taken on the day after exercising show bleeding and disruption of the Z-band filaments, which hold the fibers together as they slide over each other during a contraction.

Doctors can assess muscle fiber damage by drawing blood and checking for CPK, a muscle enzyme. CPK is found in muscles and is released into the bloodstream when muscles are damaged.

Those exercisers who have the highest post-exercise blood levels of CPK also have the most muscle soreness. Using blood CPK levels, as a measure of muscle damage, researchers have shown that running fast downhill stretches shin muscles while they contract and causes more post-exercise soreness than almost any other exercise.

Cooling down, or exercising at a very slow pace after you have exercised more vigorously, will not prevent muscle soreness.

Q: Is a slow heart rate always a sign of a strong heart? -- C.E., Hagerstown.

A: Highly fit athletes usually have slow resting heart rates because their strong hearts pump large amounts of blood with each beat. However, a slow heart rate can also mean that you have a block in your heart's electrical conduction system and your heart is damaged.

Every muscle in your body contracts in response to an electrical stimulus. The electricity for all normal hearts starts in the upper part of the heart. As the electrical impulse travels along nerves down the heart, it causes the heart to contract and squeeze blood out of its chambers to your body. After an electrical current passes from the heart, a new current starts in the same spot in the upper part of your heart. If your heart muscle or the nerves that carry the electric impulses are damaged, the electrical impulse may not get through and the heart may miss some beats, so it beats more slowly. This can be a sign that your heart is damaged. If you have a slow heart rate and exercise regularly, you probably have a strong healthy heart. If you have a slow heart rate and never exercise intensely, you should check with your doctor.

Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.

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