Ivo Siebert, 35, a semi-professional who owns a bike shop in southern Brazil, is setting the pace for the track cycling keirin event, calmly riding an electric bike while the world's fastest racers prowl behind him, preparing to sprint. "You feel that energy behind you... but you have to keep very focused, on the speed, on the curves," said Siebert, who in flapping beige trousers and black backpack looks more like a man commuting to work than an important part of an Olympic event. Tracing its roots to the gambling circles of post-war Japan, where it gained popularity for its drama and unpredictability, it first became an Olympic event at the Sydney Games in 2000. More...