"My only brief to my team was that we are not preparing an actor, we are training an athlete to win gold at the next Olympics. There was a lot of hard work, training everyday, six hours out on the field and then the gym. We had three athletic instructors, a technical expert for speed and endurance, all that is required to train an athlete," Mehra said.
Farhan's look in the film has already created quite a buzz and Mehra says the reason why that sole picture of the actor from the sets of 'Bhaag Milkha Bhaag' has generated so much response is because it is full of sincerity.
"There are so many actors playing sardars but the reason why this one has struck a chord with the audience is due to the sincerity dripping from it. The amount of hard work that boy has put in, he can one day write a book upon it," said the 'Delhi 6' maker, who will be conducting a music workshop at the IIFA awards in Singapore.
A picture from the movie shows Farhan sporting a beard, long hair and a buffed up body. Mehra says it is comparatively easier to achieve the look on the outside than feel what Milkha is like on the inside.
"The facial hair, the beard and the muscles can be done by anyone. I think why people are going gaga about his look is because he has worked on it inside out. First we worked on the emotions - a person who had witnessed the massacre of his entire family at the age of 11, what kind of an indelible mark it would leave on his psyche.
"Growing up to be a thief, wielding the knife, joining the army, and after that winning 76 of the 80 odd races he ran all over the world, breaking so many records, then losing the most important race in his life but winning in life, that's the story. So first we had to emotionally prepare the actor, that's the journey Farhan went through," Mehra said.
The director said he always wanted to work with Farhan and it was his director's instinct which led him to sign him for the role of the Flying Sikh. "It was my director's instinct. I follow my voice from within. I have always liked him as an actor.
In fact, I offered him 'Rang De Basanti', not many people know. He was quite surprised as he had never been in front of the camera before. He had just finished 'Dil Chahta Hai' and was doing 'Lakshya' at the time. I'd always seen something in him. I am glad that we are working together and he is in front of the camera," he said.
More than half of 'Bhaag Milkha Bhaag' has been shot and Mehra is looking to release the film sometime mid next year. "We have shot 60 per cent. We have taken a summer break because it is too hot to shoot up North. We resume in August and finish it by October. It'll be released sometime mid next year. It's the toughest film I have taken up so far in my career," he said.