Why are Olympians covered in big red circles?

After watching the first few days of the Rio Olympics, you may be wondering why on earth so many athletes have big red circles over their bodies.

We explain.

  • So what is it?

The marks - which resemble perfectly round bruises - are not the consequences of a heavy paintballing session or a fight with a hoover.

They are in fact the result of a treatment known as "cupping", which originated in China some 3,000 years ago.

  • How is 'cupping' done?

It involves placing heated cups on the body to create suction that draws blood to the skin's surface.

The treatment is said to promote blood flow to aching muscles and speed up recovery times.

The most obvious effect is the large red welt it leaves behind.

  • Who are the big names to give it a try?

Swimmers and gymnasts from Team USA appear to be most frequent users of the therapy - including the most decorated Olympian of all time Michael Phelps.

Phelps is seen with the marks over him. Credit: Reuters
Gymnast Alex Naddour. Credit: Reuters

And it's not just athletes who use cupping.

Celebrities such as Victoria Beckham, Justin Bieber and Gwyneth Paltrow have all said they are fans.

  • Does it hurt?

The British Acupuncture Council (BAcC) says no but some athletes disagree.

Phelps was filmed wincing in pain in a recent advert as he underwent the procedure.

Fellow US swimmer Natalie Coughlin posted a painful-looking image on Instagram with the caption: "Laughing because it hurts so bad."

One person, who underwent the treatment for back pain, told ITV News that she "would not recommend it".

"Cupping is especially painful and leaves horrendous swollen purple welts that hurt for days afterwards - I would not recommend it!"

  • Are Team GB giving it a go?

No British athletes have been seen with the red circles on their skin.

But the English Institute of Sport - the body which provides most of Team GB's nutrition, physiotherapy and sports science expertise - told Press Association Sport it is a treatment the team uses.

  • So does it work?

Depends who you ask.

Some practitioners believe it is invaluable in helping with a variety of ailments.

US gymnast Alex Naddour told USA Today that cupping was "better than any money I've spent on anything else".

However, there is no proof it has any benefits.

An experienced sports doctor who works for an Olympic team in Rio told Press Association Sport it was "rubbish anecdotal medicine" that was currently popular because athletes will try almost anything if they think it works.

Follow the latest from Rio 2016 on ITV News.