Michael Phelps of the US holds up his award recognizing him as the most decorated Olympian, during the London 2012 Olympic Games at the Aquatics Center, on Aug 4, 2012. Phelps ended his incredible Olympic career on the perfect note on Saturday, winning his 18th gold medal for the United States in the men's medley relay, the last time he will swim a competitive race. [Photo/Agencies]

Brazil's Terezinha Guilhermina, left, and her guide Guilherme Soares de Santana cross the finish line to win the women's 100m - T11 final in the Olympic Stadium at the London 2012 Paralympic Games, on Sept 5, 2012. The pair were racing against other athletes who were also visually impaired. [Photo/Agencies]