United States' men's 4 X 100-meter medley relay team from left, Matthew Grevers, Michael Phelps and Brendan Hansen shake hands with teammate Nathan Adrian after winning the gold medal at the Aquatics Centre in the Olympic Park during the 2012 Summer Olympics in London, Saturday, Aug. 4, 2012. Phelps pushed the United States in front to win the medley relay Saturday in the final swimming event of the London Games, after which he is retiring.(AP Photo/Matt Slocum)