The 26-year-old actress, who impressed with her stunts in Ek Tha Tiger, plays a gymnast in the film in which she stars opposite Aamir Khan for the first time.
A source told Mid Day: "Katrina has done some rigorous training sessions. Going by the history of the earlier two outings of the film, the leading ladies of the film are required to have great bodies. Katrina's training is a mix of martial arts, gymnastics and a bit of parkour as well."
The insider went on: "The stunt scenes are very vital to the film and after her power-packed sequences in Ek Tha Tiger, Katrina Kaif does not want to leave any stone unturned for Dhoom 3 with Aamir."
The Zindagi Na Milegi Dobara star rehearsed stunt sequences at Yash Raj's studios in Mumbai and will join the film's cast in Chicago after completing her schedule for her Yash Chopra film in Ladakh with Shah Rukh Khan.
Kaif has previously said she was nervous about the intense training required for Dhoom 3's action sequences.