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Athletes are always looking for a competitive edge over their opponents. Competitors will give anything a shot to get the advantage over their rivals whether it’s a new diet, a different stretching routine or suction cups.

That’s right. Suction cups.

During the Olympics, USA swimmers have been seen with dark circular marks around their bodies. Here is Michael Phelps walking around the pool before his 100-meter freestyle relay race.

Michael Phelps has done some cupping, which helps blood flow, in case you were worried he put cigars out on himself. pic.twitter.com/X2Uy3ftj4Z

— SPORTSBETTING (@SportsBettingAG) August 8, 2016

It looks like Phelps either lost a fight with a vacuum cleaner or is having way too good a time in Rio, but the marks are actually a result from cupping therapy.

For the past couple years, swimmers such as Nathan Adrian and Natalie Coughlin started turning to the ancient method found in China and parts of the Middle East to aid their recovery. Cupping involves heated glass cups that are applied to parts of the body. The temperature of glass creates suction that supposedly helps treat pain and relieve muscles of knots and swelling.

[Related: Katie Ledecky shatters 400 freestyle world record, nabs first U.S. swimming gold]

While the bruising side effect isn’t too sightly, athletes of Team USA swear by it.

Not only are the swimmers doing it, but the USA men’s gymnastics team is also partaking in the therapy. Instagram posts from Alex Naddour show his own marks in an effort to alleviate the pain from grinding through his sport.

A photo posted by Alex Naddour (@alex_naddour) on Aug 4, 2016 at 9:44am PDT

It seems to be working.

U.S. men’s gymnastics finished second during the qualifying round of the 2016 Olympics, and team members Michael Phelps and Nathan Adrian secured gold medals in the 4×100-meter freestyle relay.