Usain Bolt's manager says the Olympic track star is taking the rest of 2010 off because of tightness in his lower back. Manager Ricky Simms said in an e-mail this morning that Bolt has been examined by a doctor in Germany and the back problem "restricts his ability to generate power in his stride”. Simms says MRI exam showed that a previous left Achilles' tendon injury is healed but racing "in this condition could risk injury" to Bolt's legs. Bolt will have treatment to loosen his back and then rest, skipping track and field meets in Zurich and Brussels.