The round bruises are the end product of a healing technique called cupping, and Phelps isn’t the only athlete trying it. American gymnast Alex Naddour recently posted an Instagram picture of himself with a cupping mark clearly in view, gymnastics team captain Chris Brooks relies on the method and former Olympic swimmer Natalie Coughlin has sported the purple dots on her body.
“That’s been the secret that I have had through this year that keeps me healthy,” Naddour told USA Today about the therapy. “It’s been better than any money I’ve spent on anything else.”
Cupping involves heating small glass cups, then placing them on the skin and pulling them from the body to loosen and relax muscles. The resulting bruises last about two weeks.
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The alternative medical treatment may be all the rage in Rio, but it’s hardly the first time the practice has made headlines. Jennifer Aniston donned cupping spots at a movie premiere in 2013. Gwyneth Paltrow and Victoria Beckham have also tried the ancient technique.
Although modern science has not been able to confirm the benefits beyond a placebo effect, according to Business Insider‘s Rebecca Harrington, athletes swear by it.
“Our bodies are going to hurt after doing this for so long,” Naddour said. “It’s the best thing that I’ve ever had. It has saved me from a lot of pain.”
And given that Phelps took home his 23rd Olympic medal last night, it’s tough to argue.
To learn more about all Olympic hopefuls, visit teamusa.org. The Rio Olympics are currently airing on NBC.