For six months, the personal fitness trainer for Oscar Pistorius, who is to become the first double amputee to compete in able-bodied Olympics, did not know his client did not have legs, he said on Thursday.
Jannie Brooks, who has trained the South African known as the "Blade Runner" for almost a decade, said he had no clue when the athlete approached him alongside other high school teenagers for training.
"He trained with me for about six months before I knew he didn't have legs... because he was doing everything at the same pace as everybody else, no excuses for not making any exercises, he was doing it flat out.
"And at the time he started to train, it was in winter so they always had tracksuit pants on. So we trained hard ... we did explosive training ... and only once we did one exercise and he didn't go as deep as the other guys.
"I said listen you have to go a little deeper and he told me 'listen, that's the max I can go' and I said why and he said 'alright this is my story'".
To his surprise, young Pistorius was on prostheses.
"I couldn't believe it."
Pistorius, who runs with carbon fibre prosthetic running blades, had both legs amputated below the knee when he was 11 months old because of a congenital condition that meant he was born without fibulae -- lower leg bones.
At first, Pistorius played contact sports at school, but when the sportsman fractured a knee playing rugby he took to track running, and has never looked back.
He is targeting to break the 45-second barrier in the 400m at the Olympics.
He competed in the Athens 2004 and Beijing 2008 Paralympics.
Brooks and Pistorius' father, Henke are both rooting for him in London.
"I think he has a good chance. To get where he is at the moment is an amazing achievement, that is hard work and I think his chances are very good," said Brooks.
"For him to have qualified... is already an amazing thing. His chances are good," said the father.
The 25-year-old is set to compete in both the 400m and the 4x400m relay.
He is clear to compete on condition he uses the same prosthetic legs that have been used in Paralympic sport since 1996.
On the controversy that his blades give him an advantage over able-bodied athletes, Brooks said, if anything, his muscles have to work harder than runners on biological legs.
"His leverage on his legs is a lot shorter, actually it's the muscles that do the work," said Brooks.
His father, who will watch him run on Saturday, dismissed as "stupid" the notion his blades make him run better than others.
"It's stupid to even think like that. How can blades, which are latent, be something that generates power. It works against the ethics of science, you can't put something in and get more back," he said.
When he is not running, he drives fast cars.
"He likes fast cars. Every time he comes here, he's got another car," said Brooks outside the gym, a converted garage filled with training equipment.
"He is just built for speed, because the cars have an amazing performance... that I think is his hobby."