What are the dark circles on the back of swimmers?

As the swimming competitions get underway at the Paris Olympics , many athletes from across the world have dark circles on their bodies as they dive into the pool.

Michael Phelps was among the first big swimmers to have the dark round circles on his back and legs, in 2016 when he raced.

In Tokyo three years ago, Australian swimmer Kyle Chalmers was among the athletes to have the marks across his shoulders.

The marks come from cupping, an old therapy that has its roots in Asian and Middle Eastern cultures.

Scientific evidence of the benefits of cupping might not be clear, but it is believed to help relieve muscle tension and increase blood circulation.

Here’s everything you need to know about the treatment

What is cupping?

Cupping is a type of therapy that creates suction against the skin using a variety of tools including plastic cups, ceramic, bamboo or glass cups. Pressure is created inside the cup and the skin is pulled to promote blood flow to the area.

There is also “wet cupping” where less suction is used, but afterwards small cuts are made across the skin and then a small amount of blood is taken.

Where does cupping come from?

Cupping has been popular in a number of cultures including in China, Egypt and across the Middle East, and dates back thousands of years.

However, it has recently become popular because of use by celebrities and athletes, who have influenced the use of the practice across the world.

Why does it leave a mark?

The practice is supposed to draw fluid to the area, and the dark marks are because of broken blood vessels just under the skin, similar to a bruise.

How did it become popular?

Cupping was in the spotlight in the 2016 Rio Olympics when the marks were spotted on Phelps’ back, legs and shoulders.

“I’ve done cupping for a while before meets,” Phelps said during the 2016 games.

Does it have scientific benefits?

Harvard Medical School says the evidence is too limited to be able to draw a conclusion, largely because of the lack of placebo. It cites a 2015 study looking at cupping but said “the quality of the evidence was too limited to draw firm conclusions”.

Although the study in question found that the practice might provide some relief for neck or back pain.