Olympic Swimmer Michael Phelps

U.S. swimmer Michael Phelps talks to the media after his training at the Gold Coast Aquatic Center on the Gold Coast, Australia, July 15, 2011.

Michael Phelps displays his eighth gold medal after the men's 4x100-meter medley relay final at the Beijing 2008 Olympics in Beijing.

Michael Phelps competes in the 100-meter butterfly at the Indianapolis Grand Prix swimming meet in Indianapolis, March 29, 2012.

Swimmer Michael Phelps swims in the preliminaries of the 100-meter butterfly at the US Swimming Nationals in Indianapolis, August 2, 2007.

Michael Phelps and his mother Debbie Phelps attend the Heart Truth's Red Dress Collection during Fashion Week in New York, February 8, 2012.

Olympic gold medalist Michael Phelps posing in the Belmont Plaza Olympic Pool in Long Beach, Calif. (Jan 2008 file photo)