THE SKINNY ABOUT LONG-ENDURANCE EXERCISE

This tackles the myth that working out longer is good for your heart and helps you to lose weight.

   Once upon a time there was a marathon runner named Jim Fixx. Jim believed that long-duration cardiovascular endurance training was the best method for achieving optimal health. He set out preaching his message of endurance training as the key to a healthy heart and long term health. He practiced what he preached up to the day he died at the age of 52 from a heart attack while he was out on a run.

    The fact is that long-distance runners have higher rates of sudden cardiac death than do other athletes. This fact remains true for runners all over the world regardless of culture or diet. There are two ways to look at this: (1) even though distance runners run a higher risk of dying of sudden cardiac death, the probability of it happening are still relatively low; (2) perhaps there is something about long duration endurance training that contributes to heart damage. Most people will side with the first option, mostly because it fits into their world view of healthy people who exercise a lot don’t die from heart attacks, so if that does happen, then it must be the result of some kind of undiagnosed pre-existing condition. To be fair, many of the hearts examined of runners who died of sudden cardiac death showed signs of disease or abnormalities.

    Long-distance runners may actually be creating a biological condition that contributes to higher risks of heart attack or stroke. Studies show that those signs of disease and possibly the abnormalities may be the result of the endurance training, and not, as popularly believed, the result of undiagnosed pre-existing conditions. J. Sanchez-Quesada et. al. studied the blood of long-distance runners and discovered that they experienced increased levels of LDL cholesterol (the bad kind) and triglycerides. (Atherosclerosis. 1995 Dec; 111(2):297-305) In addition to increased levels of LDL and triglycerides, there was evidence of oxidation occurring. Oxidation of LDL is linked to higher risks of heart attack and stroke. The American Journal of Cardiology discovered that long-distance running disrupts the balance between blood thinners and thickeners, elevating levels of blood clotting and inflamation. (American Journal of Cardiology. 2001 Oct 15; 88(8): 920-923).

    The human body, the amazing machine that it is, adapts to any form of exercise that occurs for more than ten minutes. The body shifts to become more efficient. In essence, it downsizes. Endurance exercise decreases the size of the heart, lungs, and muscles so that they will be more efficient–they go longer using less energy. A body that is more efficient and smaller sounds like a good thing. It is exactly the kind of thing for which most Americans are shooting when they engage in some form of exercise program. The trade-off, however, is that the body loses its ability to provide short bursts of intense energy for short periods of time. The body adapts to what is going on long term and endurance training convinces the body that every time that it is being used, it is being used for long-term endurance. Therefore, the body ignores any provision for short-term needs.

    Studies show that short-duration exercise improves cardiovascular health more than long-term endurance exercise. A Harvard study compared men who engaged in high-intensity, interval exercise with those who engaged in endurance training and determined that the first group reduced their risk of heart disease by 100% than those in the second group. (Circulation. 2000 Aug. 29; 102(9): 975-980). Dr. Seiler studied athletes who ran for twenty minutes alternating between two minute intervals of running with two minutes of rest. He discovered that this form of exercise allows the body to increase cardiac output without shrinking the heart muscle. More importantly, it also allows the body to maintain it’s ability to adjust to changing cardiac demand.

    The ability to react to changing demands on the heart is important because heart attacks typically occur when there is a sudden, sizable demand on the heart or when a person is at rest. Heart attacks generally occur when someone suddenly lifts some heavy object, is having sex, or is faced with a sudden emotion blow. Endurance training is not conditioning the heart for the situations that cause heart attacks.

    It turns out that interval training is not only good for the heart and lungs, while allowing a person to maintain muscle mass, it also is better at burning fat. Colorado State University examined the duration that the body burns fat after brief periods of exercise. The participants of the study exercised for twenty minutes with two minute intervals of exercise and one minute of rest. The study found that participants still burned fat sixteen hours after exercising. Not only did they continue to burn fat longer, their bodies were burning fat 62% higher than before interval training.

    Surprisingly, the body’s highest percentage of burning fat as a source of fuel occurs when it is at rest. As long as a steady source of food is going into the body, the body will not be worried about using up its fat store while at rest. Here is how the numbers break down for the amount of protein, carbohydrate, and fat the body uses as fuel. At rest, the body will burn 1-5% protein; 35% carbohydrate; 60% fat. At low intensity the body will burn 5-8% protein; 70% carbohydrate; 15% fat. At moderate intensity the body will burn 2-5% protein; 40% carbohydrate; 55% fat. At high intensity the body will burn 2% fat; 95% carbohydrate; 3% fat. (These statistics come from Revising Energy Systems. IDEA Health and Fitness Source as adapted by McArdle W.D., et. al. 1999. Sports and Exercise Nutrition. New York: Lippincott Williams & Wilkins)

    Logic says that the longer you exercise, the more fat you will burn; therefore, the more weight you will lose. This logic comes from what the body does during exercise. When you exercise, the first thing that your body burns is fuel source called ATP. ATP is apparently the body’s energy reserve. There is only enough to last for about two minutes of activity. After that, the body switches to burning glycogen. Glycogen is a carbohydrate that is stored in muscles. Glycogen reserves will last for the next fifteen minutes of exercise. After that, the body will begin to burn fat that is stored in the body. So, the longer you work out, the more fat you’ll lose, right? Wrong.

    The reason why fat is so hard to lose, which is why you are exercising in the first place, is because your body really wants to hold onto its fat stores. Fat is the body’s insurance policy against starvation. This is why low-calorie diets don’t work. When calories are reduced, the body is forced to start burning its fat reserves. Over time, this triggers the body to think that it is starving, so it adapts, burning fat at a slower rate and turning every calorie consumed into fat. So the attempt to starve the body slim makes the body increase its fat production.

    Long-endurance exercise also triggers the body’s fat production. Since the body adapts, and endurance training forces it to burn fat, the body becomes convinced that every time it is active, it will be forced to burn large amounts of fat for fuel. This convinces the body that it will run out of fat, so it focuses on fat production. The body is going to decide that it needs to store fat so it has something to burn the next time it is active. So you exercise for an hour four times a week and burn a lot of fat. The body will compensate by taking the calories you eat and use them to make new stores of fat. So starvation diets trigger fat production, and so does endurance training. So the result is that you have to exercise longer and longer to burn the same amount of fat and lose weight because your body is convinced that it will starve to death if it doesn’t make more fat. This is why people on diets and who engage in long periods of aerobic exercise “plateau.”

    The solution is finding a way to exercise that won’t convince your body that it is going to starve. During brief intervals of exercise, the body burns ATP and glycogen stored in the muscles. Over time, this will cause your body to store more energy in the muscles and not as fat on the belly. The body notices that when it exercises, it is engaged in brief periods of activity. Therefore, the body will want to be ready for the next period of activity by storing energy in the muscles. The body won’t store energy as fat because the body is not used long enough to burn fat during exercise; therefore, since the body is constantly attempting to increase efficiency, it will decide that storing fat is inefficient because it is not burning fat as its primary source of fuel.

    This is not a theory; it is a fact! The Laval University in Quebec compared those who practiced long, moderate intensity, aerobic exercise (the condition in which the body burns the most fat during exercise) with those who practiced short interval but high-intensity exercise. The first group cycled for forty-five minutes without stopping. The second group cycled in numerous short bouts of fifteen to ninety seconds with periods of rest in between. The long duration group burned twice as many calories than did the interval group, but the interval group lost more fat. For every calorie burned by the long-term endurance group nine times as much fat was lost by the short-term group. (Tremblay A, Simoneau JA and Bouchard C. Impact of Exercise Intensity on Body Fitness and Skeletal Muscle Metabolisms. Metabolism. 1994 July; 43(7): 814-818)

    So the moral of the story is that ten minutes of exercise that incorporates differing periods ranging between low to high intensity is better for your heart and will allow you to lose more weight. (DeBusk RF, Stenestrand U, Sheehan M and Haskell WL. Training Effects of Long Versus Short Bouts of Exercise in Healthy Subjects. American Journal of Cardiology. 1990 Apr. 15; 65(15): 1179-1184)

    Next time I will examine the myth that cholesterol causes heart attacks.