Has Usain shot his Bolt?

For the first time in years the planet's fastest man is looking vulnerable. Simon Turnbull reports on whether the unthinkable might happen when he defends his sprint titles at the World Championships in South Korea
Asafa Powell is sitting in a Birmingham hotel, a black beanie hat pulled tightly over his shaven head. "This is like the North Pole for me," he says.
The heat will soon be on for Powell, the fastest man in 2011, and for his Jamaican compatriot Usain Bolt, the fastest man of all time, in the battle for the World Championship 100m title. The first-round heats take place at the Daegu Stadium in South Korea next Saturday. The final will be at 12.45pm British time a week today.