Usain Bolt blames his laid-back personality for being injured last season and insists he has learned from his mistakes, pledging to eradicate any complacency ahead of the world championships in South Korea.

The Jamaican sprinter said the back and Achilles' tendon problems that hampered him in 2010 came about due to his casualness in failing to stretch properly.

"My coach said that I will never get an easy year again because when I get it easy, I get lazy," Bolt said on Wednesday. "I think I got a little bit too laid-back last season because it was an offseason for us and I was trying to take it easy not to pressure my body too much. I backed off doing my back exercises, stuff like that. That's part of the reason I got injured last year.

"For me, the key thing is just to learn from your mistakes. So now I have learned. All I have to do now is work toward just being a better person and just being a better athlete."

Bolt made a belated start to the season because he was exempt from the Jamaican nationals for the worlds, which will be staged from August 27-September 4 in Daegu, South Korea. He still has the quickest 200 time of the year after clocking 19.86 in Oslo last month.

The three-time Olympic gold medalist will have a new bulked-up physique when he faces European champion Christophe Lemaitre of France in the 200 meters of the Areva meet in Paris on Friday.

"I've been working a lot on my back. I've been strengthening my hamstring. As you can see, I've got a little bit more muscle this year because I've been really putting a lot of emphasis on that," Bolt said. "I've set a standard for myself which is really high. People don't understand that with sport comes injury. When you get injured, it's hard to get back sometimes. You got to really work hard."

The last sprinter to beat Bolt after his victory in the 100 at Stockholm last year, No. 1 rival Tyson Gay pulled out of the US nationals last month with an injured hip and won't even run at the worlds as a relay member.