Researchers at Brigham Young University studied fluid from the knees of 30 young adults, both before and after they went for a run, Joinfo.com reports with reference to WNDU.
After just a half hour of running, their knees had less inflammation and reduced levels of a protein linked to arthritis.
On the other hand, sitting for 30 minutes increased inflammation in their knees.
Researchers say this was a small and short-term study, and they hope to do more research to see how running longer distances and different paces affect changes in the knee.