Those red circles you’re seeing on Michael Phelps and other Olympic athletes is from a therapy called cupping.
Cupping is done to help the body move blood strongly to various areas to help healing. When small round cups are used with suction or fire to remove oxygen in the cup, the suction is strong enough to rupture small capillaries just under the skin. The red circles are the result. This in different than a bruise. Small capillaries are stimulated by the suction and bring additional blood supply to the affected area, all to promote healing.
Depending on the strength of the cupping the circle marks may last anywhere from 1 day to a week or more.
Cupping has been part of Chinese Medicine for hundreds of years. Chinese medicine incorporates many modalities including Acupuncture, Chinese herbs, moxabustion, diet, exercise, sleep and life style stress. Chinese medicine has many other therapies including tui na, qi gong and tai chi which are often practiced to promote optimum health.
A little history: Cupping originated in the Middle East roughly 4000 years ago, but wasn’t mentioned in Classical Chinese texts until about 300 AD, by physician Ge Hong. The technique had spread all along the silk trade route, including Europe, Russia and Asia. Lastly, some say there is reference to cupping engraved on the great pyramids in Egypt. Either way you view it, this healing technique has been around an awfully long time.