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Blake Lively's 13 hour a day work out

Blake Lively worked out for 13 hours a day in 'The Shallows'.

The 'Gossip Girl' star says the movie's action scenes were so intense that she felt she was working out for the entire shoot.

She said: ''Well, you know, I had an amazing trainer. I was fortunate to have Don Saladino help me out and he just kicked my butt in the best way, in the most healthy way ...

''Being in waves like that, swimming like that, doing such long takes like that all the time - I became so much stronger and more fit by the end of production. I was working out 13 hours a day because shooting was working out. It was neat to be able to do that, and it was neat to have that challenge after having a baby, because you think your body is so different - you think no matter what, it's never [going to be] totally be the same.''

And the 28-year-old actress - who has 17-month-old daughter James with Ryan Reynolds - also revealed she took advice from her husband before accepting the role.

She added to Entertainment Tonight: ''He was very kind and generous to read the script. I was really sick [at the time] and I was working, and so he read it and he was like, 'Aww the action is amazing.'

''[For this film] he said, 'Be prepared, this movie is a physical challenge, it is an athletic event. It was like training for a marathon.''

Meanwhile, Blake previously revealed it was like a ''marathon'' training for the drama movie.

She said: ''It was really crazy. But it was also nice to have that motivation because I wouldn't have done that. I wouldn't have gotten in that kind of shape.

''It was like training for a marathon, but a marathon is one day. This was six weeks straight, six-day weeks, no lunch breaks, thirteen-hour days, four-foot waves at all times. By the time I was done with the movie ... I had muscles that I had never had before.''