If you’ve been watching the Olympics, you may have wondered why some athletes are sporting perfectly round, deep purple or red bruises.

As U.S. swimmer Michael Phelps celebrated his 4x100-metre relay team’s win in Rio de Janeiro on Sunday, the round bruises dotting his back and shoulders attracted almost as much attention as the 19th gold medal of his career.



The bruises are the result of a Chinese therapy technique first recorded some 1,700 years ago. It involves heating glass cups and placing them on the skin to create suction. For athletes, the goal is to loosen the underlying muscles when the cups are pulled away from the skin. The practice has also been promoted as a way to build up energy in the body and relieve it of toxins.

Some athletes are also using cups attached to a pump to create suction without heat. The treatment is not supposed to be painful but it breaks capillaries in the skin, resulting in the telltale cupping bruises.

When Jennifer Aniston and other movie stars began appearing on red carpets covered in bruises, some experts dismissed cupping as just another celebrity fad and questioned whether it has any real health benefits.

But it appears that cupping has been a part of Phelps’ exercise and wellness regimen for some time. He has posted several photos of his cupping treatments on Instagram, including this one from September, 2015.

Thanks @arschmitty for my cupping today!!! #mpswim #mp @chasekalisz A photo posted by Michael Phelps (@m_phelps00) on Sep 10, 2015 at 12:29pm PDT

An Under Armour ad announcing Phelps’ return to the Olympics also features a scene in which a therapist heats glass cups with an open flame and presses them on the swimmer’s back.

U.S. gymnast Alex Naddour, who performed during qualifications in Rio on Saturday, also had noticeable cupping bruises on his shoulders.

Naddour told USA Today that cupping has been “the secret” to keeping him healthy during training and competitions. He said he bought his own suction cups on Amazon for $15.





Natalie Coughlin, an American swimmer and 12-time Olympic medallist who is not competing in Rio, is also a big fan of cupping. Many of her Instagram photos show bruises all over her body, including legs and arms.