The reason why loads of Olympians are covered in purple bruises.

While the first few days of the Olympics have been completely dominated by swimming, it’s not the world records people are talking about. It’s the strange circular bruises on Michael Phelps’ back.

Okay, so some people are talking about the world records (Australian women’s 4 x 100m relay swimming team, we’re looking at you). But many watching at home were too distracted by Michael Phelps’ back to fully appreciate the U.S. men’s 4x100m freestyle relay win.

Does phelps have those circle bruises from cupping massages or are they marks showing he’s an alien fish in disguise… makes u think.

— Ahh, Diet Parpo|4| (@mtwundagore) August 8, 2016

Are those birthmarks on Michael Phelps’ right shoulder, or just bruises from falling down drunk? #RioOlympics2016 pic.twitter.com/3I4JnLCR09 — Cory Hughey (@CoryHughey) August 8, 2016

Why is Michael Phelps covered in circular bruises? @teach2kids80 theory was epic octopus fight https://t.co/6unBtSx9Xm

— Jeremy Mathis (@jmmath) August 8, 2016

Moments after winning his 19th gold medal (no big deal) the camera panned to Phelps, 31, and showed dark, circular bruises covering his back. And he’s not the only one—the U.S. men’s gymnastics team have been seen with similar bruises, too.

No, they didn’t just emerge from a paintball fight or a disagreement with something tentacled.

It’s called cupping. And athletes swear by it as a way to increase blood-flow and heal sore muscles.

Por que alguns atletas estão com manchas redondas no corpo? Essas manchas são provocadas pelo uso de Ventosas, que consiste em copos de vidro ou acrílico, com a finalidade de criar vácuo e fazer a sucção da pele. Ao ser realizada a sucção da pele e a musculatura para dentro do copo, o vácuo formado estimula a circulação sanguínea e com este processo são liberadas as toxinas existentes do sangue. Eu mesma utilizei a técnica está semana, devido a uma lesão muscular no ombro. Obs: É importante lembrar, que essa técnica não dói, apesar de deixar marquinhas arroxeadas . #ventosaterapia #atletas #olimpios #força #musculos #ombro #doresmusculares #relaxamento #tecnicachinesa #atletasolimpicos #ventosa #roxodobem #cupping #chinacupping #juliana_personaltrainer A photo posted by Juliana Rodrigues (@juliana_personal) on Aug 8, 2016 at 8:55am PDT

Cupping has been around forever; it dates back to the fourth century. It hit the mainstream not with an athlete, but courtesy of alternative medicine’s number-one fan, Gwyneth Paltrow. She showed up to a movie premiere 10 years ago covered in bruises, telling Oprah it was “amazing and feels very relaxing”.

Jennifer Aniston followed her lead, and now even Justin Bieber is a fan.

My body looks like eyes nose and mouth

A photo posted by Justin Bieber (@justinbieber) on Mar 31, 2016 at 12:59am PDT

The process involves heated glass cups being placed on the skin, to stimulate energy in the body.

It kind of looks like cow udders, but don’t let that deter you.

This kinda Saturday morning. Cupping is a great recovery tool #cannotwalk#everydayislegday A photo posted by Pavel Sankovich (@pavelsankovich) on Jun 18, 2016 at 8:47am PDT

Don’t let the bruises deter you either; they typically only last three days to a week. Though maybe just don’t do it before you plan to wear a backless dress.

Image: Screenshot via NBC.

This article was first published on Flo and Frank. Read the original article here.