Yohan Blake is 'legitimate challenger' to Usain Bolt - Michael Johnson

Track legend Michael Johnson said Yohan Blake, who won the sprint double at the Jamaican Olympic trials, was a "legitimate challenger" to defending Olympic champion Usain Bolt.

But the American insisted that Bolt was still his favourite to win three gold medals in London, as he did at the Beijing Games in 2008.

"Yohan Blake showed he will take advantage when Bolt does not perform at his best. Bolt now has a legitimate challenger and will need to be at his best in London to defend his Olympic title," Johnson said in an interview with Laureus.com.

"But I think Usain can do whatever he wants to do! He's got that type of talent and he wants to win three gold medals again.

"I would say if he gets to the starting line healthy, at his best, everyone else at their best, he wins every time, I mean he's just that good."

Johnson, who won four Olympic gold medals at 200m, 400m and 4x400m relay and is also an eight-time world gold medallist, added that he thought Bolt could run even faster than his 9.58sec world record.

"He could break the world record again, he could run 9.5sec, lower. Ultimately if he were to really be focused and committed on cleaning up his technique, he could probably run 9.4sec, but he would have to do some major training and adjustments in the way that he runs.

"He's not a very clean sprinter, if you look at him from a bio-mechanical standpoint. Usain Bolt could absolutely run faster, but it would take a tremendous commitment on his part to do a complete overhaul of his technique."

Johnson, who gave up a gold medal from the 4x400m relay in Sydney after team-mate Antonio Pettigrew admitted he had used performance enhancing drugs, said he felt you could never guarantee a "clean" Olympics.

"You have to also understand that you're never going to completely eradicate performance enhancing drugs from the sport and people trying to cheat," the 44-year-old said.

"That would be like thinking that some day we're no longer going to have crime in society. You're always going to have crime in society, you're always going to have people trying to cheat.

"But you also have to understand that by and large most people in society are good people and they don't commit crimes, it's the same way in sports. By and large most of the people are good people and they don't use performance enhancing drugs and try to cheat."

Johnson also said that a two-year ban for doping was not enough of a deterrent, while a life-time ban was too much, instead calling for suspensions of four years to be implemented.

"Four years would be appropriate. In a sport like athletics, in particular, if you miss four years, your career's probably over, but if you really want to try to come back and try to make things right after you've served your four years, I'm fine with that."