It might look like a giant case of chicken pox but in fact the most decorated swimmer, Michael Phelps, is hoping these spots will lead him to innumerable podiums at the Rio Olympics.
These red marks are left by cupping - a Chinese medicine technique to relieve ailments including back neck and shoulder pain.
Phelps likes the practice so much that he included images of his long muscular back being cupped in his new pre-Olympics Under Armour advertisement.
It is performed by placing cups onto the skin by way of either heat or suction.
The technique works by creating a vacuum inside a cup by inserting a flame, removing it and quickly placing the cup on to the body before the vacuum is lost leaving behind odd-looking red circles from the suction.
With his son Boomer watching from the second deck, the swimming superstar summoned a performance for the ages to propel Team USA to gold -the 19th of Phelps' career.
It has been adopted by several members of Team USA.
Here's American swimmer Natalie Coughlin getting the treatment.
“It certainly looks painful. But if it makes your muscles feel better, and gets you to the Olympics, so what?,” She wrote on Instagram.
American artistic gymnast Alexander Naddour has also found cupping provides relief from the soreness and pounding that come from gymnastics.
“That’s been the secret that I have had through this year that keeps me healthy,” Naddour said.
