US Olympian Michael Phelps is sporting large, circular bruises on his back and shoulders in Rio after undergoing the ancient therapy of cupping — but what is it?

Behind the ancient "cupping" treatment 03:18. If 19-time Olympic gold medalist Michael Phelps does it for his health, then it’s gotta be good, right?. That’s what many are wondering after ...

Michael Phelps, 31, with red welts on his back from cupping therapy. NBC There is limited research to back up the purported benefits of cupping.

Michael Phelps with visible cupping marks (Image via David Ramos/Getty Images) It was in 2016, that the bruised purple circles on Michael Phelps' back and shoulders became an Olympic moment.

If you watched Michael Phelps swim his way to his 19th gold medal in the 4x100 freestyle relay, you might have noticed round reddish-purple marks on his back and on a few of the other swimmers as ...

Yep, those round purple marks on the bodies of many competitors (including swimmer Michael Phelps and gymnast Alex Naddour) are the result of cupping therapy, an ancient Eastern medicine practice ...

Last night as Michael Phelps won his 19th gold medal in the 4 x 100 freestyle relay, many wondered: What are those purple circles on his arms and back?The marks, spotted on a number of Olympians ...

Strange round markings on Olympic swimmer Michael Phelps got a lot of people wondering what happened. Turns out, it was something called cupping. Jodie Manross has cupped clients since 2011. "It ...

What are those bruises on Michael Phelps's body? They're also appearing on more and more NBA players. SI.com examines the treatment phenomenon known as cupping.

Michael Phelps of the USA competes in the men's 200m butterfly heats on day 3 of the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on August 8, 2016, in Rio de Janeiro, Brazil. Cupping ...

Cupping therapy isn't new in many parts of the world., but the ancient Chinese practice only made it into the American mainstream a few years ago, thanks to Olympic gold medalist Michael Phelps ...

When Michael Phelps and his teammates won a gold medal on Sunday, many Olympics fans wondered: What were those purple marks on Phelps' shoulders? The bruises are caused by cupping, an ancient ...