By now you've probably seen the photos of Michael Phelps triumphantly winning his 19th Gold medal at the Rio Olympics on Sunday. (That is, if you didn't watch it live.) Phelps was also sporting some very interesting circular bruises. Although it might look like Phelps was attacked by an octopus, those bruises are actually the result of an ancient form of massage therapy called " cupping ." And Phelps isn't the only one who's into it — several gymnasts were also spotted with the spots.During a cupping massage, the therapist attaches glass or plastic cups with a bunch of suction to the skin of a particular area of your body. Sometimes this is done (quite dramatically) with the help of a flame, but it can also be done by pumping suction into the cups. Cupping is purported to help with a variety of issues — including joint pain, immune disorders, and asthma — by helping to encourage circulation in the targeted area. Athletes vouch for its ability to ease muscle soreness after training As is the case with most alternative therapies, evidence for these claims is mixed . A 2012 review of 135 cupping studies suggested that the technique may have some potential benefits (especially for relieving muscle tension ). But it also found that most of the cupping research out there is inherently flawed. Still, it isn't going to leave you with any lasting damage, so if you're into it, go for it.But, those bruise-looking things look like they hurt. What the heck does the process actually feel like? It turns out quite a few of our intrepid R29 staffers have tried it. Here's what they had to say:"I guess it feels like a combo of getting a hickey, obviously, and really good, strong massage — like when a massage therapist takes a handful of your trapezius muscle and squeezes. But the cups hold that squeeze for like 10 minutes, so it really feels like the muscles are stretching. People always ask if it hurts, because the marks can be pretty gnarly, but I think it feels great. Usually less painful than certain acupuncture points." — Amelia Edelman"I had crazy shoulder pain that was keeping me from sleeping. I couldn't get comfortable, it was in the shoulder blade... My friend does acupuncture and cupping, so I went to see her. The cupping was a little freaky because of the suction, the noises, and fire element — and just generally not knowing what would happen or what was going on. Afterwards, when I saw the cupping bruises on my back, I almost passed out — I didn't like seeing my body look so battered. [But] my shoulder pain subsided in a day! The bruises stayed for a little over a week, but I ended up being into the circle-bruise pattern... It almost looked like tattoos." — Piera Gelardi"I tried cupping for some shoulder pain I was having. My technician ...pressed a cup to my back with a slight twisting motion, which created suction. It throbbed a little, like attaching a vacuum hose to your back, but that subsided, once I got used to it, into a dull pulse of discomfort. It didn't feel awesome, but it wasn't unbearable. After what I think was 10 minutes (I might have dozed off), [the technician] removed the cups with that twisting motion. It was not a pleasant sensation. Pulling the cups off broke the suction and the skin had to be twisted to break the seal... The bruises it left behind weren't actually bruises — they were giant hickies from the suction. The worst part of the experience was having to explain to people what was all over my back for the next three days." — Megan McIntyre"Cupping, while you are getting it, feels like if someone put the mouth of a hot and high-powered vacuum cleaner on your skin and left it there for 5-10 minutes." — Kate Hyatt"I get mine right after acupuncture. It's traditional fire cupping. I've tried the suction-cup one as well; it was not nearly as good. Cupping helps release tension in muscles, and it feels tight at first, but after the cups are taken off, it feels like true pain relief. Because mine is after acupuncture needles, there can be blood that pools up as well... The cupped areas do swell up a little, but that only lasts an hour or so and doesn't hurt at all. The bruising happens every time, without fail." — Benish Shah"I tried cupping on vacation in Vietnam and it was a bizarre experience. I watched the woman do it on my cousin first, and seeing the skin get suctioned up made me nauseous before she even touched me. When it was my turn, it was very uncomfortable — a tight, hot sensation. Right after we left, I started sobbing uncontrollably in the middle of the street. Not because I was sad or upset. It just felt like some sort of emotional blockage had been released and the tears flowed. After it stopped, I felt calm and grateful and content. It was cathartic, and I'd do it again in a heartbeat." — Carolyn Todd