Paula Patton: Losing Baby Weight 'One Of The Hardest Things I've Done.'

Actress Paula Patton successfully thwarted terrorists in the latest "Mission: Impossible" film, but the real impossible mission, she says, was losing the weight she gained while pregnant with her son, Julian Fuego, just five months before the movie was shot.

Patton called the feat "crazy," in fact, in an interview with PEOPLE magazine at the launch of Reebok Crossfit Sport of Fitness campaign in New York. “It was really the most grueling and one of the hardest things I’ve done,” she said.

While she now works out for one hour five days a week, doing activities such as running, weight training, Pilates and yoga with her husband, singer Robin Thicke, she was on a much more intense regimen during filming that included two and half hours of training, six days a week.

To stay motivated, Patton told PEOPLE that she would never cry in front of her "Mission: Impossible –- Ghost Protocol" costars, Tom Cruise and Simon Pegg, though she does admit to being somewhat depressed inside.

“You have to get past that moment of self-doubt. After a month, the wall came down and the training felt doable. It still wasn’t easy, but doable and that felt really empowering,” she said.

Celebrity trainer Jeanette Jenkins -- who is also said to be prepping Beyonce Knowles for her post-baby comeback -- revealed in an interview with Hip Hollywood last summer, some of the training she did to help Patton get back on track.