What are the dark circles on swimmers' backs at Tokyo Olympics?
The alternative therapy has been around for thousands of years.
With the swimming well underway at the Tokyo Olympic games, many of the competitors can be seen covered in strange-looking dark circles as they wander around the pool and line up on the starting blocks.
But what exactly are they, and what is their point?
Well it's an ancient alternative therapy known as cupping, and is a method that has its roots in the Middle East and Asian cultures.
It involves creating suction on the skin using cups. This causes blood to flow to the area of suction and is thought to decompress the muscles and connective tissue of the area.
The cups are only placed on the skin for a few minutes, but this is long enough to cause capillaries just below the skin's surface to rupture, which creates the bizarre-looking circles on the skin.
In recent years, the likes of Dwayne 'The Rock' Johnson and Conor McGregor have been advocates of the technique, and at the Rio 2016 Olympics, the great Michael Phelps could be seen covered in the brown circles.
He explained at the time that he mainly gets the treatment on his shoulder as that's where he experiences the most pain.
He said: "That's where I usually hurt the most [and] I've done it before meets, pretty much every meet I go to.
"I just asked for a little 'cupping' yesterday because I was sore and the trainer hit me pretty hard with one and left a couple of bruises."
The practice is used by many athletes to aid recovery, but despite its claims to having a whole host of benefits, the science is a bit sketchy on this.
The US National Center for Complementary and Integrative Health has said that "not enough high quality research" has been carried out to establish whether it has any benefits or not.
- Does The Rock’s ‘cupping’ treatment really work? We asked an expert
- Does ‘cupping’ work, or is it a fashionable fad? A doctor weighs in
Meanwhile a study published in the Journal of Traditional and Complementary Medicine in 2019 suggested that the damage to the skin caused by the technique may spark a process in the body that inhibits pain. However, the study also acknowledged that "large randomised clinical trials, systematic reviews and meta-analyses in future" are needed to reveal its full effects.
So it's safe to say that the jury is still out on the technique. But now you know the mystery behind those weird brown circles.