Bollywood Mantra reports that Kaif, who stars alongside Aamir Khan in the film, has been undergoing rigorous training sessions.
"The sessions are basically to determine what my stamina is like and how much I can take. Which is what is scaring me," she said.
Kaif, who is said to be playing a gymnast in the film, was full of praise for her co-star, commenting: "Just look at him. He's maintained himself so well. It's amazing."
She added: "Women can`t work out so strenuously like that, you know. Our shoulders are not so strong. You ask a woman to do pull-ups and you'll know."
Kaif reportedly insisted on a no-bikini clause for the third film in the Dhoom franchise.