Heart Health and Marathon Running: Preparation is Key
Posted February 13th, 2007 at 3:02 PM by Megan Hueter
Section: News & Results, Marathons, Running & Training, Injury & Rehab, Training Tips, Health & Fitness, Injury & Rehab, Exercise
The risk of death from coronary heart disease is decreased almost two-fold in physically active people. Regular exercise has beneficial effects on blood pressure, lipid profile (fats in the body), insulin resistance (ability to break down sugar to use for energy), and overall decreased risk of death.
However, prolonged exercise (such as a marathon running) is hard for the body to endure, especially the heart. The risk of a cardiac event is there, as indicated by dozens of emergency crews present at various intervals of an event such as the Boston Marathon. A 2006 study shows that heart damage from a marathon is significantly related to inadequate training and preparation; a problem seen in some amateur marathon runners.
Research studies have shown associations with pathological changes in the blood and the heart which can infrequently cause acute myocardial infarction (sudden heart attack). Currently, risk factors for the development of signs of myocardial (heart) damage or dysfunction are unknown. However, the 2006 study performed by Neilan and colleagues shows that training preparation for a marathon plays a key role in the amount of heart damage that can occur.
The 2006 study looked at runners participating in 2004 and 2005 Boston Marathons. The study shows the completion of a marathon as associated with evidence of cardiac dysfunction and injury, and this risk is increased in those participants with less training.
In order to grasp the development of cardiac injury, one must understand the stress upon the heart during exercise (see diagram). The human heart has four chambers: left and right thin-walled atria (on top), which receive blood, and left and right thick-walled ventricles (underneath), which pump blood. Veins carry blood into the atria and arteries carry blood away from the ventricles.
During strenuous exercise (like a marathon), the human heart works very hard, working to get oxygen and glucose (energy) to the muscles faster. The heart also works to get heat, lactate and carbon dioxide away from the muscles faster. When there is an increase in exercise, the muscles respire faster, and therefore need a greater oxygen supply. This can be achieved by increasing the amount of blood flowing through the capillaries at the muscles. Therefore, the heart works even harder to get blood to these areas of the body.
The ventricles of the heart are very important in comprehending exercise and its affect on the hearts of marathon runners. The walls of the left ventricle are about three times thicker than the right, because this area of the heart pumps blood out of the heart under high pressure through the aorta to the muscles of the body which need energy.
The right ventricle (thinner than the left) pumps blood to the lungs (which are very close, so it requires less force). The right ventricle of the heart sends blood via pulmonary arteries to the small arteries in the lungs. Mean pulmonary arterial pressure (mPaP) measures the average strain of pulmonary arteries.
As mPaP increases, the muscles within the walls of the arteries may tighten up. This makes the inside of the arteries narrower. There is less room for the blood to flow, and the arteries can stiffen. Over time, some of the arteries may become completely blocked, causing the right side of the heart to work harder, which eventually could lead to heart failure. The 2006 study by Neilan and colleagues found increased mPAP’s, inversely related to average training mileage.
Often, highly-trained elite marathon runners have a very thick wall of the left ventricle. As elite marathon athletes train over time, the left ventricle wall grows out (meaning the heart grows stronger and releases blood more efficiently), and not in (as with an individual with a heart disease, whose left ventricle has grown inward and therefore cannot release enough blood to the body).
During diastolic (rest) function, the ventricles fill with blood. During systolic (contraction) function, ventricles discharge blood either to the lungs (right ventricle) or to rest body (left ventricle). During rest, typical healthy adult heart pumping volume is about 5 liters/min. During exercise, maximum capacity pumping volume extends from about 25 liters/min for non-athletes to as high as 45 liters/min for Olympic level endurance athletes. The difference is tremendous, due to the efficiency adaptations made by the heart with exercise training.
The human heart contains cardiac troponin T levels (cTnT). cTnT is a thin filament protein which takes part in muscle contraction. When there is damage to the heart, cTnT is released. Often, cTnT levels are measured to determine heart damage.
The 2006 study by Neilan and colleagues looked at 2004 and 2005 participants in the Boston marathons. The participants included 41 men and 19 women with an average age of 41 years (range 21 to 65). The study targeted non-elite athletes. The mean training mileage was 42±9 miles/wk, and the average finish time was approximately 4 hours (range: 2 hours 55 minutes - 5 hours 55 minutes). All runners demonstrated weight loss. Heart rate increased and systolic blood pressure decreased after the marathon.
With prolonged exercise, the study found increased right ventricle dimensions (the part of the heart that pumps blood to the lungs), as well as increased mPAPs (mean pulmonary arterial pressure, the arteries which pump blood from right ventricle to the lungs). The study also found decreased right ventricle function, which correlated with release of cTnT, a possible indicator of heart damage.
The study also found alterations in left ventricle diastolic (resting/filling) function. Most importantly, these changes were strongly influenced by the level of preparation undertaken by amateur athletes. The majority of the abnormal changes in cardiac structure or function as well as cardiac biomarker (cTnT) changes were seen in those athletes training Your browser may not support display of this image.35 miles/wk before the marathon (those less prepared for the marathon).
It is very important for everyone to understand the type of impact that strenuous exercise can have on their bodies. This is especially true for amateur marathons runners, who can put themselves at risk for heart damage (and a host of other injuries) if they fail to adequately train. Conversely, it should be emphasized that exercise (even marathon running) and maintaining an active lifestyle - with prepare care, physician consultation and preparation - can not only be safe, but also offers a myriad of physical, mental and emotional benefits.
Research sources and for more information: [BiologyMad.com] , [Runner’s World],
Neilan TG, Januzzi JL, & Lee-Lewandrowski E. Myocardial injury and ventricular dysfunction related to training levels among nonelite participants in the Boston marathon. Circulation. 114:2325-2333, 2006.
Persistent and reversible cardiac dysfunction among amateur marathon runners. (European Heart Journal, May 06)
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