Michael Phelps was creating a wave even before crashing into the pool in his fifth Olympics - and winning a record 19th gold medal.

The most decorated Olympian ever revealed a peculiar pattern of purplish-red circular blotches on his body when he disrobed prior to the United States' triumphant 4x100m freestyle relay Sunday night.

It's not the first time Phelps, or any Olympian for that matter, has been spotted with these ... spots. But with the world tuning in for Phelps' first race in his fifth Olympic games, these odd hematomas - the product of a restorative healing technique called "cupping" - took on global exposure.

Essentially, cupping is creating a suction on the skin to stimulate blood flow, and therefore, promote healing and reduce pain. Best of all, it's cheap: U.S. gymnast Alex Naddour (below) told USA Today Sports he bought a contraption for $15 on Amazon - and he swears by the results.

Heading to another training. One day closer to our goal!!! #TEAMUSA I hope everyone is ready for opening ceremonies tomorrow!!! A photo posted by Alex Naddour (@alex_naddour) on Aug 4, 2016 at 9:44am PDT

Some athletes choose cupping because they believe it relieves pressure on muscles, tendons, ligaments, and joints, rather than using force to stimulate relief, like a massage.

Its benefit, though, is disputable. There's no firm scientific evidence to suggest that cupping has a restorative advantage. But if we've learned anything about athletes, and especially ones of Phelps' stature, it's that they're creatures of habit who don't question methods they believe enhance their processes.