If you've been keeping a close eye on this summer's Olympic Games, you may have noticed some competitors with sore-looking red marks on their bodies.

Michael Phelps is among them, while the marks have also been spotted on a number of other (predominantly American) athletes. But what do they mean?

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We were at as much of a loss as many of you, but it turns out the marks are a result of a process called 'cupping'. Still none the wiser? Well, the BBC report that the process involves heated cups being placed on the skin, with the marks being caused by suction. Olympians such as Phelps use cupping for a number of reasons, including improving bloodflow, easing recovery, and just general pain relief. And it's not just Olympians - Justin Bieber has shown off marks from cupping in the past, while Gwyneth Paltrow and David Beckham are also thought to have indulged. https://twitter.com/amykuretsky/status/755760605596975108 Some scientists have dismissed cupping as a 'fad', enjoyed by celebrities but possessing of no tangible benefit. That said, if athletes enjoy a placebo-like effect from the process which helps them gain an extra tenth of a second on their rivals in an Olympic setting, does it really matter if the benefits are ultimately mental rather than physical?