"U.S swimmer Michael Phelps competes in the 4x100-meter freestyle relay on Sunday, August 7. The red marks on his body are <a href=""http://www.cnn.com/2016/08/08/health/cupping-olympics-red-circles/index.html"" target=""_blank"">the result of cupping</a> -- an ancient therapy that has mostly been used in Middle Eastern and Asian countries, especially China."