Asafa Powell and Tyson Gay fail drug tests

Last updated at 06:04
Tyson Gay and Asafa Powell

Some superstars of sprinting have failed drugs tests ahead of next month's world championships.

Former 100 metres world record holder Asafa Powell of Jamaica and the American Tyson Gay - the joint-second fastest man over 100m - have both tested positive for banned substances.

Powell denies ever knowingly taking illegal drugs, meanwhile Gay says he's been let down by someone he trusted.

Four other Jamaican athletes, including the Olympic relay gold medallist Sherone Simpson, have also failed drugs tests.