Ask Doctor Cory.

Dear Dr. Cory:

Why do you get cramps if you do not exercise or stretch before a basketball game? Why are you sore after a basketball game? How can you run out of energy after you run?

Willie Snifflett Stocks Elementary School Tarboro, North Carolina

Dear Willie:

Muscle cramps usually occur when you exercise a muscle that you usually don't, or when you overuse a muscle.

Muscles get their energy from food and oxygen in the blood. But when muscles work too hard and fast for the blood supply to keep up, like in a race, they use stored food and work for a while without oxygen.

Waste products, like lactic (LACK-tik) acid, build up in the muscles, creating muscle cramps or soreness.

Warm-up exercises and stretches get food and oxygen to your muscles to get ready for exercise. Cool-down exercises and stretches also flood your muscles with oxygen to wash away the lactic acid.

Stretches should not be bouncy or painful. Stretch only to the point of tightness, not pain. Then hold for about thirty seconds and relax.

Gentle muscle activity, like easy swimming, jogging, or fast walking, in the days after hard activity, will help to improve circulation to the muscles and ease muscle soreness, if there is no muscle injury.

Dr. Cory:

How is it that you have more bones when you are a baby than when you are not a baby?

B.J. Stocks Elementary School Tarboro, North Carolina

Dear B.J.:

Most of us are born with more than 300 bones, but only have 206 by the time we're grown up.

This is because as we get older, some of our bones join together, or fuse (fyooz). For example, babies are born with eight bones that make up the skull. This allows the baby's head to pass more easily through the birth canal. The six gaps between the bones also give our heads room to grow.

These bones gradually fuse to become one bone, which makes the skull stronger.

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Muscles need time to build strength. For an activity using the same muscles over and over, they'll need to be built up gradually.

The more you use muscles, the longer they will last without running out of energy. That is because they gradually get better at using their energy and better at removing lactic acid and other waste products.

Sincerely, Cory SerVaas, M.D.