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Know When to Stop Exercising

After you have played a long tennis match on a hot summer day, you feel weaker and less accurate with your shots. The fatigue, muscle weakness, tired aching feeling and decreased coordination that you get in any sport lasting several hours is caused by low levels of fluids, salt or calories. There are no early warning signals. By the time you feel hungry, you have already run low on calories and are ready to crash. By the time you feel thirsty, you are already severely dehydrated and feel weak and tired. By the time you are low on salt, you already have tired, aching or burning muscles; feel weak, tired and dizzy; and may already have muscle cramps.

The primary limiting factor in sports that require great endurance is the time it takes for your heart to pump oxygen in your bloodstream from your lungs into your muscles. A study from the University of Connecticut (Medicine and Science in Sports and Exercise, May, 2006) shows that with dehydration, your heart beats with far less force so it pumps far less blood with each beat, and is unable to bring as much oxygen to your muscles.

You can't depend on thirst to tell you when you lack fluids. Certain brain cells called osmoreceptors tell you when you are thirty, but only after the salt concentration of your blood has risen considerably. When you exercise, you sweat. Sweat contains far more water than salt in comparison to blood. So you lose far more water than salt during exercise and blood levels of salt rise. By the time that a your blood salt concentration is high enough to trip off the osmoreceptors, you are severely dehydrated and it is too late for you to be able to drink enough during exercise to catch up with your water deficit. On the other hand, if you take salt with fluids, then your blood salt levels rise faster and tell you that you are thirsty earlier.

There are other reasons that you should take salt with fluids during prolonged exercise. First, it helps prevent muscle cramps. Remember, during exercise you lose salt and water. If you are replacing only water, you can eventually take in so much water that your salt levels drop to cause muscle cramps. Second, even though salt is a mild diuretic at rest, during exercise it helps your body to retain water. So when you are going to exercise for more than a couple hours, particularly in hot weather, drink small amounts frequently and eat salted foods such as peanuts. Always stop if you feel sick, have chills, headache, severe muscle burning or aching, dizziness, or blurred vision. Seek help if your symptoms do not subside in a few minutes; you could be headed for heat stroke that can kill you.


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Dear Dr. Mirkin: How does weight loss affect your heart?

A study from Turkey shows that the heart beats with greater strength when a person loses weight (Heart Vessels, March 2006). The obese patients in the study received echocardiograms to predict their risk for heart failure by measuring their left ventricular function. After they lost at least ten percent of their total body weight, the strength of the contractions of their hearts increased significantly. This study shows that weight loss should be part of the treatment for heart failure if the person is overweight. It also explains why being overweight makes you tired and short of breath, because your heart has to work much harder to push blood through blood vessels blocked by fat. Losing excess weight improves heart function and also helps to prevent diabetes, heart attacks, strokes, kidney damage and even certain cancers. Best diet for heart health and weight loss


Dear Dr. Mirkin: Are there any drugs to make athletes stronger that are not banned by sports authorities such as the Olympic committee?

Yes; some athletes take estrogen blockers and human chorionic gonadotropin (Journal of Clinical Endocrinology & Metabolism, Volume 91, 2006). Estrogen blockers such as Tamoxifen, Arimedex, Aromasin, and Femara are used to treat women with, or at high risk, for breast cancer. Evidently lowering the female hormone, estrogen, may act the same way as raising the male hormone, testosterone, to help athletes recover faster from hard workouts. Human chorionic gonadotropins are hormones that are produced in very large amounts by a woman's body when she is pregnant. These hormones appear to promote cells growth, which includes muscle tissue.

Both male and female athletes can experience strength gains from these hormones or anti-hormones. Since nobody really knows all the side effects that occur when healthy athletes take them, the athletes may be risking their lives.


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June 26th, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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