AP
Jamaica's Usain Bolt was one of the most exciting athletes at the 2008 Beijing Games. And in the last four years bolt has managed to fend off his rivals.
Until now. Fellow Jamaican Yohan Blake looks to challenge Bolt's dominance on the track. Also, you can't discount the U.S. who consistently field some of the fastest men in the world. Can Bolt fend off these challengers and defend the 100 metre title?