Training for your first marathon is exciting. If you’re a runner, this is probably something you’ve been thinking about for years. But you may have heard that distance running isn’t good for you. Critics say it’s too much for the body to handle, but fans of the sport say it makes them feel more empowered than ever. We broke down the truth about distance running and whether or not you should click that “sign up” button and take on your first marathon.

Running is not bad for your knees

Contrary to what you’ve heard, running is not bad for your knees. Running doesn’t cause arthritis. (However, if you are already suffering from arthritis, running can amplify the problem.) Actually, some studies suggest that running can even help your knees in the long term. Mindy Solkin, founder and CEO of The Running Center in New York City, told WebMD that most running-related injuries are likely due to the runner’s form and how much you’ve run. “You can run without injury; you just have to know your limits,” Solkin said. Ask a personal trainer to help with your form if you think it could be leading to injuries.

If you have a pre-existing heart condition, distance running might not be for you

Some people avoid distance running because they’re worried about the strain it could put on their heart. Between 2000 and 2010, there were 42 cardiac-related deaths either during or immediately after running a marathon. However, almost all of these were due to an underlying, undiagnosed heart condition. In young people, the heart condition is often a genetic abnormality that goes undiscovered. In older people, it’s typically undiagnosed heart disease. Consult your doctor before taking on something as intense as running a marathon. It is always better to be safe than sorry.

Throughout the years, evidence about running’s benefits has been murky

You might have heard distance running is bad for heart health, but that’s because studies have shown that too much running can harm you in the long run (pun intended).

In 2012, a Kansas City cardiologist named James H. O’Keefe published a study that concluded distance running could have potential negative side effects, such as fibrosis, calcified arteries, and arrhythmias. Scientists agree that it’s difficult to measure humans’ heart health in relation to running, because there are so many contributing factors to heart health: smoking, genetics, distance run, years of running, etc.

… But heart health appears to depend a lot on distance

According to Runners World, a study done over the course of 15 years found that those who regularly ran up to 20 miles per week were 19% less likely to die than nonrunners. However, runners who ran more than 20 miles per week did not see a significant difference from nonrunners.

Based on the study, distance running is great, but excessive running won’t give you the same benefits. Those who ran 20 miles or fewer per week showed a lesser risk of heart-related death over the years. With that said, those who ran more than 20 miles per week, more than six days per week, or more than eight miles per hour, didn’t seem to reap the same health benefits.

The sweet spot: Fewer than 20 miles per week

In order to get the maximum heart and health benefits running can offer, it’s important to not work yourself too hard. Exercising anywhere between five and 19 miles per week, at six to seven miles per hour, appeared to be the best consistency to improve heart health over time, according to the study.

If you don’t have a pre-existing heart condition and can follow a professional marathon training plan, running a marathon will likely be an awesome experience. However, it’s still important to consult your doctor first to make sure the intense running will agree with your body.