 Complete the following phrase:  Nothstein won his first world championship medal in 1993, when he took the silver in the keirin. He became a double world champion in 1994, winning both sprint and keirin events at the 1994 World Championships. He did so while nursing a broken heel bone. Nothstein again rode with a fractured bone, this time a kneecap, as part of the U.S. team sprint squad that won the bronze medal at the 