Bolt maintains improvement over longer sprint

Jamaican triple Olympic gold medallist Usain Bolt effortlessly won his second 400 metres test in a week, running 45.54 seconds at Kingston's National Stadium last weekend.

The world 100 and 200 metres 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 metres races to help him increase his stamina as he prepares for his main focus of outdoor season, the 100 and 200 metres. 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 metres at the Beijing Olympics and ran on Jamaica's world-record breaking 4x100 metres relay team.

After one false start, the lanky sprinter shot to the front 70 metres 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.

Meanwhile, Russian pole vaulter Yelena Isinbayeva enjoyed an easy victory at the Birmingham Grand Prix with a clearance at 4.82 metres on Saturday.

But the Olympic champion, who plans to skip next month's European Indoor Championships, failed to break the indoor world record of 5.00 metres she set the week before in Ukraine.

Mo Farah proved his preparations were well on track for the the continental indoor championships by smashing his own British 3,000 metres indoor record.

The Somali-born 25-year-old raced to victory in seven minutes 34.47 seconds, six seconds faster than his previous mark.