Race walkers are reflected in a puddle as they compete in the 50km event. Toby Melville / Reuters

Michelle Carter of the US, on her way to the gold medal in shot put. Kai Pfaffenbach / Reuters

Anchor runners in a 4x400m relay heat await the baton hand-off. Martin Meissner / Associated Press.

China's Liu Hong (left) and Lyu Xiuzhi refresh themselves during the 20km race walk. Damir Sagolj / Reuters

The world's fastest man, Jamaica's Usain Bolt, readies for the start of the 200m final. Alessandro Bianchi / Reuters

Croatia's Blanka Vlasic bends over the bar during high jump qualifying. Dominic Ebenbichler / Reuters

Britain's Mo Farah crosses the finish line to win the gold medal in the 5,000m. David J. Phillip / Associated Press

New Zealand's Eliza McCartney reacts to clearing her second leap in the pole vault final. Matt Slocum / Ap