How endurance running can damage your health

In our culture, marathon runners and triathletes are often seen as the picture of perfect health and physical stamina. But before you add a marathon to your bucket list, it behooves you to know that pushing through pain to achieve feats of endurance can be risky, even for those of you who are in good health. The latest research on the topic has stopped many long-distance cardio fiends in their tracks, and it may mean you never look at that treadmill in the same way again.

In recent years, overwhelming evidence has emerged to prove that endurance exercise can have dire health consequences.

In a 2011 study published in the Journal of Applied Physiology, male endurance athletes who trained the longest and hardest for races showed significant muscle scarring. In the most extreme cases, scarring of heart muscle can lead to cardiac arrest and death.

That same year, a study published in the European Heart Journal revealed that practiced endurance athletes suffered from diminished heart function and had increased cardiac enzymes in their blood (markers for heart injury) after a race. And the longer the race, the greater the decrease in their heart function.

In perhaps the most confounding finding, endurance runners were shown to have more calcified plaque in their arteries than those who don’t engage in this form of exercise, according to a 2010 study presented by the American College of Cardiology. This is believed to be due to the fact that damaged heart muscle increases inflammation in the arteries, which in turn leads to plaque formation.

Even if you’re not an endurance athlete or aiming to be, this evidence is enough to make you reconsider how many miles you log on that treadmill. The research suggests that extended episodes of cardiovascular exertion without proper recovery can be dangerous for athletes and non-competitive runners alike.

Indeed, the risks don’t end there. Extreme endurance cardio has also been associated with acute rises in cortisol levels that can persist and lead to muscle loss as well as lowered immune function. Chronic elevated cortisol puts the body into a catabolic state, which means it starts breaking down your muscle and tissues for energy.

I can testify to this, personally. A couple of years ago while training for half marathons and triathlons, despite working out for 12 hours per week, I found myself losing muscle and suffering from low back pain and injuries. If you need more proof, just compare photos of the 2013 New York City marathon winners Geoffrey Mutai and Priscah Jeptoo, who look emaciated, frankly, with the much more muscular Olympic sprinter, Usain Bolt. Sprinting allows you to run for shorter lengths of time at a higher speed and intensity.

Does this mean you can never run or cycle again? Of course not. And most Americans would do well to exercise more. Thankfully, there is a way to challenge your body, build strength and stamina, and protect your heart all at the same time. High-intensity interval training (HIIT), which consists of short bursts of high-intensity exercise with adequate rest in between, has been shown to be safe enough for heart transplant survivors—and this form of exercise takes less time, to boot. Since I made the switch from endurance to interval training, I’m in better shape, with more muscle and less fat, than I ever was as a long-distance triathlete.

Here are my tips for building a safe, heart-healthy fitness routine:

1. Go from long runs to short bursts. Rather than running a consistent, moderate pace (45 minutes at five miles an hour, let’s say), convert your time on the treadmill into high-intensity bursts. Warm up for three to five minutes, and then run as hard and fast as you can for one minute. Recover for two minutes. Repeat this for the duration of your workout, which needs last no longer than a half hour.

2. Strengthen your core. Incorporating core-strengthening exercises into your weekly fitness routine can help support your back and make you less prone to injuries.

3. Rest and recover. Balance out your exercise regimen with 7-9 hours of sleep per night and good nutrition to give your body sustained energy and optimize its ability to recover.