Here's what you should know about the ancient practice embraced by U.S. Olympic athletes

This week everyone’s talking about cupping, a therapy that some Olympic athletes competing in Rio have been partaking of. It caught people’s attention this week because the therapy often leaves round marks that look like bruises on the skin, but it’s certainly not new. The practice has been used in ancient Chinese medicine for thousands of years as a way to treat pain, muscle stiffness and even respiratory issues.

Perhaps one of the most notable athletes to sport the signature cupping marks is Michael Phelps. Other athletes, including swimmer Natalie Coughlin have also embraced the practice. “That’s been the secret that I have had through this year that keeps me healthy,” said American gymnast Alexander Naddour, USA Today reports. “It’s been better than any money I’ve spent on anything else.”

So how does cupping work? Either heat or air is used to create a suction in special cups that are placed on the body. The vacuum that’s created pulls the skin and blood vessels in toward the cup, which is why they can leave marks on the skin. Cupping is thought to pull blood to a certain area, and improve circulation and loosen up muscles and joints. There’s also some suggestion that it has anti-inflammatory effects. In the U.S. it is sometimes used in addition to acupuncture or massage. A specialist can apply the cups, though as USA Today reports, some athletes say they are doing it themselves.

Read the full report here.