Usain Bolt taking rest of 2010 off due to back injury

Usain Bolt of Jamaica reacts after he won the men's 100 meters at the IAAF Diamond League athletics meeting at the Stade de France Stadium in Saint-Denis, near Paris July 16, 2010.LONDON, Aug. 11 -- Olympic and world champion Usain Bolt said on Tuesday he won't race again in 2010 because of tightness in his lower back.Ricky Simms, the Jamaican's manager, said in an e-mail that the world