Research clearly shows regular exercise in moderation, particularly aerobic exercise, lowers the risk for atherosclerotic heart disease and stroke. It does this in a number of ways – by benefiting lipid levels, lowering blood pressure and, possibly, by reducing inflammation inside blood vessels. Inflammation is now linked with heart disease as well as a variety of other disease states. For all of these reasons, the American Heart Association recommends at least 150 minutes of moderate exercise or 75 minutes of vigorous exercise each week as part of a heart-healthy lifestyle.
Even more surprising is the fact that regular physical activity also changes the structure of your heart. Your heart is divided into four chambers. The upper chambers are called the atria while the lower chambers are called the ventricles. The left atria and ventricle receives oxygenated blood from your lungs and pumps it to the rest of your body. The right atria and ventricle receive deoxygenated blood from your body and your ventricle pumps it to your lungs to be re-oxygenated. The left ventricle is the portion of your heart that has to generate the most force since it has to send blood to all the tissues in your body. Therefore, it’s the largest.
The Effect of Aerobic Exercise on Your Heart
Aerobic exercise and resistance training both change the structure of your heart, but in slightly different ways. After about three months of regular endurance exercise, the left ventricle in your heart begins to enlarge by dilating. Over time, the left ventricular wall becomes slightly thicker as well.
Why do these structural changes take place? During exercise, your muscles and tissues require more oxygen. To meet the demand, the left ventricle dilates and the ventricle walls thicken so it can pump a larger volume of blood to the tissues that need it. During endurance exercise like long-distance running, the amount of blood your heart pumps increases by as much as eightfold. As a result, your heart becomes more efficient at delivering oxygenated blood to your hard-working muscles. In turn, your aerobic capacity increases and you develop greater endurance.
Other adaptations take place as well that increase aerobic capacity including an increase in capillary density around muscles so they can get more oxygen and an increase in mitochondria, the organelles inside muscle cells that produce ATP.
At one time, it was thought that only the left ventricle changed in size in response to endurance exercise. Research now shows the right ventricle becomes larger too. Structural changes to the heart in response to exercise are sometimes called “athlete’s heart.” You can also see ventricular enlargement with certain types of heart problems including disease of the heart valves, damage due to a heart attack or long-standing high blood pressure.
The difference is athlete’s heart is associated with normal heart function whereas enlargement due to heart disease is not. Also, the changes in the ventricles of the heart in response to heart disease or hypertension cause the ventricle to become stiff. As a result, they don’t function as well. These changes are irreversible while athlete’s heart reverses if you stop exercising.
How Resistance Training Affects Your Heart
Your heart also adapts to resistance training, but the changes are different than with endurance training. When you do resistance exercise, your systolic and diastolic blood pressure both transiently rise. This rise in blood pressure, however brief, places pressure on the left ventricle (the one that pumps blood to the body) to become “stronger” so it can pump against the higher pressure and resistance. As a result, the wall of the left ventricle becomes thicker. Unlike endurance training where the main adaptation is an increase in the volume of the ventricle, the left ventricle adapts to resistance training mostly by becoming thicker.
How Your Heart Changes Depends on the Type of Training
The way your heart changes structurally in response to exercise depends on the type of training you do. If you’re primarily a strength athlete, your left ventricle will become thicker but the size of the left ventricle won’t change as much. If you do mostly endurance exercise, both your right and left ventricle will dilate and increase slightly in size.
These changes aren’t absolute, especially if you do both resistance and endurance training. In this case, you’ll probably have some degree of ventricular enlargement and thickening of the walls. Interestingly, women usually have less pronounced “remodeling” or changes in heart structure in response to exercise compared to men.
Athlete’s Heart
Athlete’s heart, structural heart changes related to exercise, is believed to be a benign condition caused by the stress of training. The increased ventricular size and thickness usually return to normal after about 3 months of not exercising. But in about 20% of athletes, the enlargement and wall thickening doesn’t subside. This usually requires further investigation, including imaging studies, to look for underlying heart problems.
Some experts question whether long periods of endurance exercise like running a marathon or an ultra-marathon could cause permanent remodeling of the heart itself. Some studies show an increase in proteins in the blood suggestive of injury to the heart after very long periods of intense exercise. Makes you wonder about the long-term risks of running marathons or triathlons. Fortunately, you don’t have to train for a marathon to stay in great shape.
The Bottom Line?
Exercise affects your heart in a number of ways and even changes your heart structurally, although these changes are usually reversible. The way your heart responds to endurance exercise is different than the way it adapts to resistance training. Your heart adapts to handle higher blood pressure in response to resistance training while it changes to carry an extra volume of blood during endurance training. Most importantly, exercise lowers your risk for heart disease in a number of ways. Just as your other muscles change in response to exercise, so does your heart.
References:
Science Daily. “How Exercise Lowers Cardiovascular Risk”
Neth Heart J. Apr 2008; 16(4): 129-133.
Med Sci Sports Exerc. 2013 Mar;45(3):534-41. doi: 10.1249/MSS.0b013e3182780b0e.
Merck Manual. “Athlete’s Heart”
J Am Coll Cardiol Img. 2009;2(3):350-363. doi:10.1016/j.jcmg.2008.12.011.
Circulation. 114 2006:2325-2333.
Am J Cardiol. 83 1999:1085-1089.
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