You're at match point and suddenly your calf muscle cramps, forcing you to leave the tennis court. Or you're in the last few miles of the cycling portion of a triathlon and a leg cramp slows you to a crawl.
We don't have the foggiest idea what causes muscle cramps. One theory used to hold that it had something to do with blood chemistry. But now studies show that crampers and non-crampers have the same blood levels of calcium, sodium, magnesium and potassium.
Crampers and non-crampers also suffer from the same degree of dehydration, have the same level of fitness, train by doing the same amount of exercise and have similar increases in body temperature when exercising.
The vast majority of muscle cramps strike their victims after more than 90 minutes of exercise. During a recent marathon, for example, leg cramps hit many runners after 14 miles while more than one-third occurred during the final mile.
If you develop a muscle cramp while you are exercising, stop. Knead the muscle with your fingers and stretch it out. If the cramp is in your calf muscle, stop exercising, pull the front part of your foot up with one hand and massage the muscle with your other hand.
If you suffer from frequent muscle cramps during exercise, check with your doctor. He or she can run tests to see if you have a pinched nerve, a blocked artery, a mineral or thyroid abnormality, or a disease of muscle metabolism.
If no cause is found, try to work up to the point where you can exercise for more than two hours, once a week; drink plenty of fluid at the start and at least every 15 minutes during your workout. If you are primarily a vegetarian, add some salt to your food, but do not take salt tablets.
Q: How can I tell if I'm overexercising?
A: If you feel good when you exercise and your joints and muscles do not feel sore, you're probably getting the right amount of exercise.
When you exercise too much, you will stop looking forward to each new workout. Your joints and muscles will be plagued with soreness and a burning sensation that becomes most severe when you start your workout.
Some people are so obsessed with exercise that they do not listen to their bodies. They continue pushing the limits of their workouts and end up injured or sick. These athletic overachievers need an objective test to warn them when they are exercising too much. This test should be done only by people who have healthy hearts.
First, exercise flat out for at least five minutes; then stop. Place your fingers on the side of your neck where you feel your pulse. Count your heart beat for six seconds. Exactly 60 seconds later, take your pulse again for another six seconds. Subtract the second pulse rate from the first and then multiply that number by 10. This final number is your recovery pulse rate per minute.
If you do this test once a week, you will soon find out what number is "normal" for you. An increasing recovery pulse rate means that you are training well. A decreasing recovery rate means that you should take a day off.
Q: Is it possible to overdose on vitamins?
A: Megadoses of any vitamin can be dangerous, even fatal. Vitamins have specific functions in your body. When you get more of a vitamin than you need, these functions can be exaggerated and can harm you.
Taking large amounts of vitamin D, for example, can make your body take in too much calcium and can cause you to develop kidney stones and calcium deposits in your muscles. Excessive amounts of niacin can damage your liver and can lead to very high blood sugar levels.
Fat-soluble vitamins, like vitamins A, D and E, are stored in your body. They can build up to toxic levels if too much is consumed.
Taking more vitamins than you need will not make your reactions any better or faster. In fact, extra vitamins are wasted. More than 80 percent of a gram of vitamin C, for example, is excreted in your urine shortly after you take the vitamin.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.