'Well, you know, I had an amazing trainer,' she told ET. '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,” the 28-year-old continued. “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."
Lively spent eight weeks filming the shark thriller in Australia
Lively and Ryan Reynolds, welcomed daughter James in December 2014.