The following story is excerpted from TIME’s special edition, The Science of Exercise, which is available at Amazon.
There’s no denying that running is one of the most democratic ways to work out. You can do it anytime, anywhere, and all you need is a good pair of running shoes and some stamina. It’s no wonder, then, that more and more Americans are adopting the sport and doing it competitively; the number of people who finished organized races grew 300% in the U.S. from 1990 to 2013, and in 2015, there were slightly more than 17 million Americans who ran in races nationwide.
Still, estimates suggest that 79% of runners will get injured at some point, a statistic that’s remained relatively stable for more than 40 years. “Running is hard on the wheels, especially if you’re doing long-distance running,” says James O’Keefe, a cardiologist at St. Luke’s Mid America Heart Institute in Kansas City and a former runner. “A lot of people will break down orthopedically.”
Since more than 80 million Americans are living a sedentary lifestyle, there are certainly plenty of people who could benefit from running rather than doing nothing at all—and if you do run already, there is no reason to stop unless a doctor tells you to. The latest science on running and its effects on the body offers both encouraging and cautionary takeaways for people who enjoy the sport.
Running may prevent some injuries
Running has a reputation for causing wear and tear, but new research suggests that it may actually prevent injuries rather than increase the risk of them.
A small study published in December 2016 found that 30 minutes of running lowered inflammation in runners’ knee joints. In the report, researchers at Brigham Young University brought 15 healthy runners into a lab where samples of their blood and knee-joint fluid were taken before and after they ran for 30 minutes. The researchers then compared the samples with ones taken earlier when the men and women were sedentary.
The researchers expected to find an increase in molecules that spur inflammation, but they didn’t. Instead, they found that pro-inflammatory markers had decreased. “It was surprising,” says study author Matt Seeley, an associate professor of exercise science at BYU.
Seeley emphasizes that the report is a pilot and that his team plans to do the same study with more people in the near future. “I think, and hope, the data will show that running is good for your joints,” he adds. “Although the results are limited, they are also unexpected and could be important.”
Not everyone is convinced. “There is data on both sides of the fence,” says Brian Feeley, an orthopedic surgeon at the University of California, San Francisco, who wasn’t involved with the study. “We know there are some people who run all the time with no problems and others that have arthritis at a relatively young age.” For now, people of all abilities should allow themselves time to recover post-workout.