Michael Phelps woke up on the morning of the first race of his fifth Olympics with some soreness in his right shoulder.

At 31 years old, the swimming superstar could not afford to have anything slowing him down. So he went to a Team USA athletic trainer for some cupping therapy - a treatment he has been receiving for years to help relax his muscles and ease soreness.

"The trainer hit me pretty hard with one and left a couple of bruises," Phelps said.