Oscar Pistorius shocked the athletics world this week when he qualified for the World Championships - but should he be allowed to race against his able-bodied rivals?
The South African double amputee, who competes on carbon fibre legs, in Italy on Tuesday to qualify for the championships in Daegu next month and also set up a possible Olympic bid.
Pistorius was cleared to compete by the International Association of Athletics Federations in 2008 after a lengthy legal battle but his new-found speed reopens the debate.
BBC Sport asked Olympic silver medallist Roger Black and British 400m record holder Iwan Thomas for their views.
"Personally I am amazed at the time he ran. He was running OK times for the past few years but he was never going to challenge the best in the world.
"And as long as he was doing that, it was fine. But now he is moving into territory which is starting to get interesting.
"If he gets down to 44.5 seconds, then it changes the whole discussion because nobody knows whether his blades are an advantage or not.
"They have not been around long enough. We don't know if Oscar is an amazing athlete, or a very good athlete with an advantage.
"What if a kid comes along with the talent of Michael Johnson but has an accident and then runs 41 seconds?
"This is a whole grey area. It is a celebration of human endeavour on his behalf but you will see a lot of 400m runners complaining.
"Emotionally, I would love to see him race but, if I had to go one way or the other, I would say he shouldn't be able to race because we are not seeing like against like.
"The faster he runs, the more people are going to say that he has an advantage and we are not on a level playing field.
"I can only imagine how I would feel if I raced against him in the Olympics and he beat me. Now he is a real threat and a real player on the world stage, other athletes will say that it is unfair."
"I am delighted for Oscar. I tweeted him as soon as I woke up this morning.
"We all know what a quality athlete he is and he has shown just how hard he has worked over the last couple of years and the self belief he has got.
"If you look at the 400m on the world stage this year, it's not that strong an event so this performance has put Oscar right up there.
"It gives him a chance of making the final of the World Championships - and that would be great for the sport it that happens.
"The IAAF has cleared Oscar to run against able-bodied athletes so that's the end of it as far as I'm concerned. People might come out of the woodwork now and argue that it's not right but it is only because he is running such fast times.
"What Oscar has achieved also shows people that there are no limits.
"There may be kids with a disability who look at him and see him beating able-bodied athletes.
"You need role models in life and he gives people hope. If he can do it, anybody can do it."