Have mark, will win. (Lee Jin-man/Associated Press)

Michael Phelps and the Olympic swimmers arrived in prime time Sunday night, and there was something unmistakable on their bodies: round circles.

They weren’t the result of a tattooing misadventure or a secret symbol known only to members of the swim team. Either of those would have made a great story. The circles came from cupping, a technique used by trainers who attach suction cups to pull blood to sore and injured areas to speed healing. A recent Under Armour video shows Phelps receiving the treatment, as he has done for years. He also posted a photo on Instagram last year, telling fellow Olympian swimmer Allison Schmitt, “Thanks for my cupping today!”

At about the 1:30 mark of Under Armour’s video, you’ll see what cupping looks like. (Or if you pay attention to all things Gwyneth Paltrow, you’ll know.) If you’ve ever had it done (I have, but not because Gwyneth recommended it), you’ll find it relaxing and it does seem to make your muscles feel better — perhaps because it stretches tendons and muscles differently than massage.

“It looks like we get attacked by octopuses,” said three-time U.S. Olympian Dana Vollmer, fresh off a bronze medal in the 100 butterfly.

The cups, which create suction with either heat or little pumps, aren’t attached for long, and the discoloration is the result of broken capillaries that occur as the skin is pulled up into the cup.

“Keep in mind that it’s superficial bruising. So it’s not real bruising,” American Cody Miller, bronze medalist in the 100-meter backstroke, said. “So if you get hit really hard and you bruise, it’s not that kind of bruise. Your muscle tissue isn’t torn up in there. It’s just pulling blood into a specific area, and then it just kind of sits there as that tension builds and then you release that tension.

“It’s great,” Miller added before explaining that he purchased his set on Amazon for $20. “I use it a little bit. My fiancee, Ali, right there does it to me during training. I’ll have her put cups on there and she’s like, ‘Aaaaah, so gross.’ But it’s cool.”

Does it work? Experts are divided on the matter. But if you believe it works, you’re likely to perceive that it’s beneficial. I haven’t had it done lately, but I’m an Olympic blogger, not an Olympic athlete. Would I have it done again? Sure.

U.S. swimmers seem to be sold, at least.

“I think it works great for a lot of us. A lot of us use it,” Vollmer said. “Not all of us have quite as many cup marks as some of the swimmers that we’ve seen with them on. Nathan [Adrian] and Michael [Phelps] love it. It works really well for them.”

Swimmers aren’t the only ones who are trying the technique. Alexander Naddour, a Team USA gymnast, sported circle bruises.  Alexander Naddour, a do-it-yourself cupper thanks to a kit he bought for $15 on Amazon, was sporting the purple dots during competition Saturday in Rio. “That’s been the secret that I have had through this year that keeps me healthy,” Naddour told USA Today. “It’s been better than any money I’ve spent on anything else.”


Alexander Naddour has the same mark, in the same place, as Phelps. (Alex Livesey/Getty Images)

Barry Svrluga contributed to this report.