This post was written by Michelle Ward Trainor and originally appeared on People.com

Kate Upton is used to tough workouts, but her latest left the supermodel a bit sore.

The Sports Illustrated Swimsuit cover model participated in Workout with the Marines on Tuesday to raise awareness for Marine Week Detroit (running Sept. 6-10) and the Patriot Ruck on Sept 9. The event was organized by Wins for Warriors – a charity founded by Kate's fiancé, Detroit Tigers pitcher Justin Verlander – which supports military service members and their families.

“It was definitely a very intense workout, but I had a lot of fun. I’m feeling it a little bit today!” Kate, 25, told PEOPLE the day after the grueling routine, which included seven rounds of intense exercises such as burpees, toe-touch squats, push-ups and sprints. “I always knew the Marines are very disciplined, but, man they really didn’t let me get away with anything. I thought they’d be ok with me having a little bit of a cheat on those numbers but no, you do those 10 pushups!”

But Justin, 34, was on hand to offer support. “Justin came to cheer me on. It was funny because I heard a switch in his cheering. At the beginning he was laughing at me, preparing to make fun of me and then there was a dramatic change when he was like, man, this is really hard. [He said] ‘You can do it, Kate! Keep going!'” she says with a laugh.

“I normally do a mixture of body weight training and weight training [so this] was different than how I do workouts, and I think that’s why I was also really excited to switch it up,” she explains. “To make sure you’re body doesn’t get too used to just one type of workout. It’s ultimately way more difficult when you’re not used to the workout.”

Both fitness enthusiasts, Kate and Justin also find was to keep in shape together.

“Justin and I, in the off season, we go to the gym at the same time, but we don’t work out together because I do weight training for a woman’s body, and Justin’s training is specifically to help perform in pitching, and to help him sustain longevity,” she says. “But then when we’re both done at the gym, we stay very active whether it’s playing tennis or going on a hike or a bike ride, things like that.”

So, after working out with the Marines, would Kate be up for it again?

“Oh absolutely,” she says without missing a beat.

BONUS: See all of Kate's amazing photos from SI Swimsuit 2017!