American swimmer Michael Phelps has won more Olympic medals than anyone in history. On Sunday night, he added another gold medal as a member of the USA 4x100-meter freestyle relay team. But the red circular marks on Phelps’ upper arms and shoulders received most of the attention. Television viewers wondered what caused the marks on his body. Athletes in other sports had similar marks. It turns out they are bruises left behind from a treatment called cupping. Cupping is supposed to help athletes who have sore muscles feel better. A study published earlier this year in the Journal of Bodywork and Therapies calls cupping “an ancient technique used in treating pain and various disorders.” Forms of cupping may have started over 5,000 years ago.