KINGSTON (AFP) - Reigning world and Olympic sprint champion Usain Bolt will return to basics when he runs the 100 metres on Thursday at the Jamaica Athletics Championships to prepare for the World Championships.

He had not planned to run at the national trials for the Jamaican squad who will compete at the worlds later this year at Beijing, having already assured himself of a spot in the field.

But his failure to run under 10 seconds in the 100m or under 20 seconds in the 200m so far this season has bewildered the global sprint star. It has forced coach Glen Mills to change plans and enter him in the Jamaican trials that select athletes for the worlds and next month's Pan American Games in Toronto.

Bolt has byes in both the world 100 and 200 after winning both events two years ago in Moscow, just as he did at the 2008 Beijing Olympics and 2012 London Olympics.

But while making the team is not a concern, finding form is a worry.

He took last season off to rest and underwent a medical procedure to prepare for what he says are his final three years of competitive track and field, a span in which he wants to secure his legacy and create history as the only man to win three straight Olympic sprint doubles.