Credit: X17online

Hilary Duff is going to be one buff bride!

Ahead of her walk down the aisle this weekend, the actress has been hitting the gym hard five days a week with intense cardio sessions courtesy of celeb trainer Harley Pasternak.

Circuit training is Duff's key to toning up.

"Each workout starts with a cardio warm up of jump rope and jogging, then we do a circuit of upper body, lower body and abdominals," Pasternak, who also trains Duff's NHL player fiance, Mike Comrie, tells "We go through each exercise and do about 25 reps. We'll repeat that circuit about four times and then end with cardio at the end."

The celeb trainer and author of The 5-Factor World Diet (Katy Perry is also a fan), Pasternak says Duff has also revamped her diet.

To prep for her big day, Duff followed her trainer's diet plan, noshing on foods like egg white omelets, chopped salads, and her personal favorite, Miso black cod.

"[Hilary] had a different motivation because she was getting ready for her special day. She's really noticed a huge difference, practically all over," Pasternak tells Us. "She looks phenomenal. We trimmed her midsection, so it will be tight. Her arms look amazing."

Pasternak says he can't wait to see Duff and Comrie become husband and wife.

"They are both dear friends, and I wish for them to have the most amazing life together," he tells Us.