What Really Happens to Your Heart During a Marathon

You’ve likely felt the surge of adrenaline rip through you as you line up at the start of a big race. The gun goes off, and with every step you take, your heart pounds. It pounds with excitement, adrenaline, nerves, and, of course, intense exercise.

That heart-beating-out-of-your-chest feeling is normal and perhaps familiar. While it’s not anything special, it’s a good reminder that your ticker plays a pretty big role both during and after your race. But what exactly happens to our most vital muscle as it adapts to the demands of a marathon? And is it safe?

The heart’s primary role is to deliver enough oxygen- and nutrient-rich blood to your muscles over 26.2 miles. To do this, it not only beats faster but also pumps more blood with each beat, a combined effect that can raise total cardiac output by up to eightfold.

Here’s a closer look at what happens to your heart during a marathon.

1. Your Adrenaline Spikes Even Before the Race

Your heart rate goes up a bit before the race when adrenaline spikes, but for most people, it’s not a concerning amount, according to Dr. Gregory Katz, MD, a cardiologist at NYU Langone Health.

When you’re nervous, an area of your brain called the amygdala sends a distress signal to the hypothalamus, your brain’s command center, according to Harvard Health. The hypothalamus activates your fight-or-flight response, and your adrenal glands start producing the hormone epinephrine. As epinephrine gets pumped through your bloodstream, your heart beats faster than normal, sending blood to your muscles, heart, and other organs. Your pulse rate and blood pressure go up, and you may start to breathe faster.

2. Your Heart Finds a New Operating Level

When you begin running, your heart rate shoots up because it’s now not only responsible for pumping blood throughout your body, but your working muscles, according to cardiologist Dr. Eamon Y. Duffy, MD, MBA, FACC, assistant professor of medicine at Columbia University and founding director of the Columbia Runners Heart Clinic. Your blood carries oxygen and nutrients to your muscles—the fuel you need to run a marathon, Duffy explains.

“I would encourage people to think of their heart as a muscle the same way they think of their leg muscles. It’s a very specialized, very important muscle in your chest that’s pumping blood to the rest of your body so it can get the nutrients and the oxygen that your body needs to run a marathon,” Duffy says. “When you run a marathon, usually you’re running at about 70%  to 90% of your max heart rate for three, four, or five hours, and so that’s how your heart responds.”

When the force with which your heart contracts increases, that’s also accompanied by changes in your blood pressure, adds Katz

“For most people, what happens is their heart rate goes up and their blood pressure goes up also,” Katz says. “The amount that those things will change is proportional to age, level of training, and a million other individual factors.”

As the race goes on, your heart rate generally doesn’t ever go back down, according to Katz. “Many runners experience something called cardiovascular drift, where the heart rate progressively increases as the body struggles to maintain cardiac output as we get a tiny bit dehydrated during the race,” Katz says. “We may subjectively feel better [as we settle into the race], but it’s unlikely the heart rate is coming down.”

3. Your Heart May Leak Troponin Throughout the Race

Duffy goes on to explain that some runners’ hearts leak troponin into the blood during the course of a marathon. Troponin is a cardiac enzyme present when there’s stress or injury to your heart. For instance, high troponin levels may be a sign of a heart attack.

For this reason, previous research, like this 2012 article in Missouri Medicine, has considered long-distance running harmful to the heart. However, a new study in JAMA Cardiology shows that while runners frequently show elevated levels of troponin in their blood immediately after a marathon, the heart typically recovers within days and isn’t a sign of permanent heart damage.

Most of the prior studies of cardiac abnormalities or cardiac damage in marathon runners have been snapshots of single time points or single days after a marathon, Duffy explains. But the recent JAMA Cardiology study kept track of participants’ heart function for over 10 years following a marathon and with continued long-distance running.

Troponin rises in the setting of a heart attack are oftentimes due to cell death within the heart because cardiac cells aren’t getting the oxygen they need, Duffy explains. But when it comes to cardiac stress in the setting of the marathon, more than likely it’s not due to cells within the heart dying but instead, more likely due to those cells working really hard and experiencing high stress. In that process, proteins from within the muscle cells of the heart can leak out, and those proteins are troponin.

4. Your Heart Goes All Out at the End of the Race

In the later stages of the marathon, there may be additional upward drift toward your max heart rate as the race goes on and we approach the limits of our conditioning, Katz explains. You may also experience an additional rise in adrenaline levels as the race goes on, he says. This may be due to the physical stress on your body and the mental stress of finishing well.

5. Your Heart Rate Comes Down Right When You Stop Running

Everyone has a different baseline level of overall fitness and adaptability to things that are potentially stressors, like running 26.2 miles, according to Katz. For most people who train appropriately and have a good baseline level of conditioning, their blood pressure and heart rate come down right after their race and they’re totally fine.

6. Your Heart Recovers in the Days and Weeks Afterward

Duffy explains that it has to recover from a marathon just like your legs do. “A marathon is an enormous physiologic stress on the body, and that stress is felt by all of the organs in the body—the heart, the brain, the lungs, the muscles,” he says. “The marathon really pushes people to the max that they’re capable of, and the same way you get fatigue in your quads, that same fatigue is being felt by the heart as well.” (He recommends at least a few days to weeks of rest after a marathon for your heart to recover from the effort.)

When it comes to troponin, Duffy says the recent study in JAMA “provided some reassurance that running a marathon imposes an acute stress on the heart, but the heart is able to recover in the days following, and over the long-term, that acute stress doesn’t lead to long-term cardiac dysfunction.”

His TLDR: “For the vast majority of runners, marathon running is safe and good for cardiac health and performance.”