Bolt maintains improvement over longer sprint

KINGSTON, Jamaica, February 21 (Reuters) - Jamaican triple Olympic gold medallist Usain Bolt effortlessly won his second 400 meters test in a week, running 45.54 seconds at Kingston's National Stadium Saturday.

The world 100 and 200 meters record holder, who claimed his first race of the year in 46.35 seconds a week ago, made it look easier this time, as he secured victory in the last of seven heats with the fastest time of the day.

Bolt is using the 400 meters races to help him increase his stamina as he prepares for his main focus of outdoor season, the 100 and 200 meters. He hopes to duplicate his 2008 Olympic victories in the two events at August's world championships in Berlin.

Bolt broke the world record in both the 100 and 200 meters at the Beijing Olympics and ran on Jamaica's world-record breaking 4x100 meters relay team.

After one false start, the lanky sprinter shot to the front 70 meters into the race and never looked back as he won by a comfortable margin from the eight-man field including two South Koreans who are training in Jamaica.

A crowd of 5,000, angered by the late-running meeting, cheered all the way as Bolt again slowed toward the finish line.

He slumped to the ground after the race and was swarmed by a crowd of officials including medical personnel, who helped him stretch and rub his hamstring.

(Editing by Gene Cherry in Raleigh, North Carolina, and John O'Brien)