By Alexandra Sifferlin
August 11, 2016

HOW IT WORKS

Administrators place special suction cups on a subject’s body, which pull skin and blood vessels away from the muscles (hence the dark marks). It’s meant to improve circulation and loosen up tissue, muscles and joints.

WHY IT’S TRENDY (AGAIN)

Swimmers say cupping helps prevent soreness, promote faster recovery and/or make muscles move more easily. In traditional Chinese medicine, it’s thought to help improve the body’s chi, or energy flow.

WHAT SCIENCE SAYS

A 2010 review of 550 clinical studies found evidence that cupping may help ease pain without any serious side effects. Some question whether there’s enough data to prove that it is definitely effective.

Contact us at editors@time.com.

This appears in the August 22, 2016 issue of TIME.

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