You may have noticed some strange red marks on the shoulders of Michael Phelps at the Rio Olympics and wondered what's going on.
They are not a niche swimming injury or birthmark we've never noticed before, but the results of a form of acupuncture called "cupping".
The treatment involves lighting a flammable liquid in a jar which is then placed on the body to create suction that draws blood to the skin's surface.
Its advocates believe it promotes blood flow to aching muscles and speeds up recovery times, although the most obvious effect is the large red welt it leaves behind.
Phelps 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."
Several other American Olympians have also been sporting the distinctive red marks, which fade after a few days, and gymnast Alex Naddour told the USA Today newspaper that he and his team-mates apply the suction cups to each other.
No British athletes have competed in Rio with "cupping" marks visible on their skin yet, but the English Institute of Sport - the body which provides most of Team GB's nutrition, physiotherapy and sports science know-how - said it is a treatment the team uses.
Simon Spencer, EIS's head of physiotherapy, said: "'Cupping' is a form of complementary therapy where glass or plastic cups are applied to the skin using a vacuum.
"There is no conclusive research evidence for its efficacy from clinical trials but some athletes report anecdotal beneficial therapeutic effects following treatment.
"Within the English Institute of Sport, some physiotherapists and soft tissue therapists may choose to use 'cupping' as an adjunct therapy, however this would only form a small part of a comprehensive evidence-based approach to athlete management and rehabilitation."
It's hardly cutting-edge science, the technique has been used in China for 3,000 years, but its popularity has grown as celebrities such as Victoria Beckham, Justin Bieber and Gwyneth Paltrow have all said they are fans.
But research to support the claims made for "cupping" is non-existent, and one very experienced sports doctor who works for an Olympic team said it is "rubbish anecdotal medicine" that is currently in vogue because athletes will try almost anything if they think it works.