The star worked with lots of different fitness pros to make sure she was ready to play Mera, the love interest of Jason Momoa's "Aquaman", including trainer to the stars Gunnar Peterson.
Talking to The Hollywood Reporter about their intense sessions, Gunnar says he was blown away by Amber's efforts.
"(She) worked like an animal," he enthused.
Together they trained for 60 minutes three times a week, sessions Amber had to fit in around all of her other training, including fight preparation.
"They were a full 60-minute hour, make no mistake about it," Gunnar stated, adding that finding time in her busy schedule was often the hardest part of the job.
Among his go-to moves were dumbbell squat presses, hip bridges targeting the glutes and core and shoulder endurance work on a Synergy Air Power Tower, and he explained how he honed in on movements and exercises that enhanced strength and flexibility.
"You have to train the body as a whole, shoring up any weaknesses -- but the hardest part about that is finding any weaknesses on Amber!" he praised.
Amber recently revealed the extent of her training in a chat with Shape magazine.
"I did six months of rigorous training. It was a lot of weight and strength training, as well as special martial arts training. By the end, I was working out for five hours a day," the 32-year-old said.
"Aquaman" is in cinemas now.