With any cardiovascular exercise, your heart works hard to pump blood through your body. The blood will reach all the muscles that you use during training, providing nutrients that will help sustain activity and endurance. For marathon runners, especially, increased cardiovascular is vital to maintain performance through the gruelling 26.2-mile event.

However, running more than 5 hours per week can produce lasting effects on the runner’s heart and body function. The most profound change is an enlarged heart, or, runner’s heart. Though this a shocking physiological change to one of the body’s most vital organs, it’s essential to understand how the transition occurs while also understanding its positive and negative effects.

The Strongest (Muscular) Organ

The heart is the central component of the cardiovascular system, the system in which blood is pumped throughout the body through blood vessels, veins, arteries and capillaries. While autonomously pumping blood to muscles and other vital organs, the heart provides much-needed nutrients to the extremities to fuel everyday life. Because the heart works so efficiently at pumping blood throughout the body, it is encompassed by four different chambers to maintain proper blood flow. These chambers are:

  • Right atrium – receives blood from veins and pumps to right ventricle
  • Right ventricle – once blood is received from the right atrium, blood is pumped to the lungs, where it is loaded with oxygen.
  • Left Atrium – receives oxygenated blood from the lungs and pumps it to the left ventricle
  • Left ventricle – the strongest chamber, the left ventricle pumps oxygenated blood to the rest of the body

During exercise, your muscles are working harder than they would in a passive state. While muscles are working hard during physical activity, nutrient-rich blood needs to be supplied to these muscles to maintain performance. Your heart then works harder to pump oxygenated blood throughout your body, keeping you from getting winded during intense activity.

Cardiovascular Health

Like any aerobic exercise, cardiovascular exercises are encompassed by movements or activities that rely on oxygen as a large component to produce the energy needed to sustain activity. During these activities, the heart must adapt to the stresses of the training. As activity increases or intensifies, the demand for blood during exercise will increase, stimulating your heart to meet the demand by increasing the rate and force that it contracts.

Your heart will have more beats per minute, and a more forceful contraction each time it beats so it can pump a significant amount of blood throughout the body. With increased cardiovascular endurance, the heart and lungs will both become more efficient in their respective roles, improving cardiovascular health. Some common cardiovascular exercises include:

  • Running
  • Biking
  • Fast walking
  • Burpees
  • Bear Crawls
  • Swimming
  • Basketball, soccer, volleyball
  • Hiking
  • High-Intensity Interval Training
  • Kickboxing

Benefits of Cardiovascular Exercise

  • Lowered blood pressure – as the heart adapts to cardiovascular exercise, it will become more robust and efficient at pumping blood through the body. The heart can pump more blood with less effort. The less effort coming from the heart can, in turn, decreases the force placed on arteries, lowering blood pressure.
  • Improved mood
  • Reduced risk of osteoporosis
  • Improved sleep
  • Lower risk of cardiovascular disease
  • Stimulated weight loss when paired with diet.

Marathon Runners at Risk

While a cardiovascular exercise like running provides many physiological and mental benefits, the risks of a 26.2-mile marathon run can be more daunting than the feet itself.

Dr. Paul D. Thompson, chief of cardiology at Hartford Hospital in Connecticut, states:

“Cardiovascular endurance can help reduce the likelihood of heart disease…but the hearts of marathon runners can harbour fatty plaques that may break free and clog an artery, leading to cardiac arrest.”

He further acknowledges, surprisingly, that this risk is heightened in runners. Because marathon runners run at such great lengths, repeating these runs overtime can be detrimental to the tissue of the heart. Repeated long-distance racing can potentially cause scar-tissue buildup on the heart tissue. It is often a result of excess stress placed on the heart during prolonged, repeated exercise, leading to arrhythmias, cardiac arrest and even death.

Marathon runners are 25% more at risk for runner’s cardiomyopathy. This condition involves the right atrium and right ventricle dilating, increasing the force of which blood is pumped throughout the body. This process is repeated for the duration of the marathon run, overloading these chambers to sustain nutrient-rich blood throughout the body. It then forms a buildup of scar tissue in the heart muscle, causing cardiac events.

Heart Disease in Marathon Runners

Despite running being an excellent source to improve cardiovascular health, marathon runners with heart disease must be especially careful when training for and participating in these events. Marathon runners might have heart tissue scarring, an enlarged heart from excess stress or a preexisting condition of which they may not be aware. Either way, they should undergo a thorough clinical evaluation to determine the severity of their condition so they can, in turn, modify their running schedules and durations.

Finding the Runner’s Heart

Though there are no objective symptoms associated with runner’s heart, low resting blood pressure, low heart rate, and irregular heartbeats can be indicative of a change in the cardiovascular system. You usually make clinical diagnosis using:

  • Doctor’s evaluation
  • ECG (electrocardiogram) screening
  • Stress testing

The Right Amount of Running

For experienced runners, paying attention to mileage, blood pressure, heart rate and recovery are all crucial factors in maintaining proper cardiovascular health. While cardiovascular exercise can help reduce the risk of heart disease, too much stress on the heart tissue can be detrimental to one’s health. Especially in those with a family history of heart disease, speaking thoroughly to physician about starting or continuing exercise can help you formulate a plan specific for you and your cardiovascular health.