Jamaica's Usain Bolt (in yellow) starts his men's 100m semi-final. - Photo by Reuters

Jamaica's Usain Bolt celebrates after winning the men's 100m final at the athletics event. - Photo by AFP

Gold medallists Serena Williams (center, L) and her sister Venus Williams of the U.S. are flanked by silver medallists Andrea Hlavackova (far left) and Lucie Hradecka of the Czech Republic and bronze medallists Nadia Petrova (far right) and Maria Kirilenko of Russia during the presentation ceremony for the women's doubles tennis. - Photo by Reuters

Iran's Hamid Soryan Reihanpour reacts after defeating Azerbaijan's Rovshan Bayramov on the final of the Men's 55Kg Greco-Roman wrestling. - Photo by Reuters

China's Zhou Lulu competes and wins the women's +75kg group A clean and jerk weightlifting competition. - Photo by Reuters

Great Britain's Andy Murray (C), Switzerland's Roger Federer (L) and Argentina's Juan Martin del Potro pose on the podium with their gold, silver and bronze medals respectively, at the end of the men's singles tennis tournament. - Photo by AFP

Aleksandr Onishchenko of Ukraine rides his horse Comte D'Arsouilles in the equestrian show jumping team competition. - Photo by AP

Germany's Andre Wessels and Peter Joppich (top) celebrate winning against the U.S. at the end of their men's foil team bronze medal fencing competition. - Photo by Reuters

British track and field athlete Jessica Ennis wears her heptathlon gold medal while greeting fans at the BT London Live concert. - Photo by AP

Hungary's coach Andras Meresz, top right, shouts as his team gathers around his arm after beating Russia 11-10 during their women's water polo quarterfinal match. -Photo by AP