Mysterious dark circles have been spotted on some of the swimmers' backs at the Tokyo Olympics, which has left the nation scratching their heads. But there's actually a simple explanation for it.
Team GB has already achieved some gold medals from the swimming so far, with Tom Daley and Matty Lee winning the 10m synchronised dive, and Adam Peaty claiming gold in the men's 100m breaststroke.
And there are plenty of opportunities for Britain to strike gold again in swimming, with more events to come between Thursday 29th July and Sunday 2nd August.
What are the dark circles on swimmers' backs?
Spectators have been left a bit puzzled as to why some of the swimmers' bodies have black circle-shaped marks on their backs and shoulders.
It's down to a form of alternative therapy lots of athletes use called 'cupping,' which is an ancient form of Chinese alternative medicine to help with inflammation, pain and blood flow.
Athletes train incredibly hard to stay on top of their game around big sporting events and working hard means relaxing hard too.
What is cupping therapy?
Cupping therapy is all the rage among sportsmen and women at the moment, but it's not a new thing and it's actually been around for centuries, dating back to around 1,500 B.C.
Basically, a therapist places small hot cups on the affected area for a few minutes to create suction, which effectively delivers a deep tissue massage and improves blood flow to the area.
The cups are typically glass, but they can also be made out of bamboo, earthenware or silicone, and they can either be wet or dry.
What happens is the therapist will put a flammable material inside the cup, like paper, herbs or alcohol and set it alight. When the flame dies, the cup is placed on the patient's skin and as the air inside the cup cools, it creates a vacuum, which draws the blood near the surface of skin.
The dark circles you can see on athletes' skin is a result of the blood being drawn near to the surface of the skin, the same way that a bruise forms when you hit yourself. It's not harmful and it helps their muscles to release after an intense training session or after competing.
Adam Peaty reportedly has this form of therapy to stay in tip-top condition for competing and Tom Daley has been known to have cupping too.
Daley once said in an interview that in the lead up to a big event, he has daily massages and yoga sessions to help his muscles unwind after training - some life eh!
Featured Image Credit: PATopics: Health