Anyone watching Sunday's night telecast of the Olympics likely had the same question ahead of the U.S. men's 4x100 freestyle relay: What were those dark red circles covering Michael Phelps' body?
It's the result of a recovery method Phelps and other U.S. athletes, including gymnasts, use to relieve tension in their muscles. The technique relies on suction cups that pull the skin back and loosen muscles and tendons, unlike a massage where they would be pressed.
It might look a little ridiculous, but athletes are notorious for utilizing whatever recovery methods work.
You can see the technique in the Under Armour bit below at the :45 second mark. Cupping "can be done with heat by lighting flammable liquid in a glass cup and suctioning that to the back once the flame goes out, with the decrease in temperature creating the suction," as
Phelps made his Rio Olympics debut Sunday night, swimming second behind Caeleb Dressel. Ryan Held will swam third and Nathan Adrian, America's best sprinter, anchored them to a gold medal.
USA TODAY's Rachel Axon detailed in a recent story.