Pop star Britney Spears' boyfriend, trainer Sam Asghari, has opened up about her fitness regime.

"(Britney) is a natural born athlete, so the info she has about working out combined with what I know about fitness, is what you see when we collaborate on new moves that we do together," Sam told eonline.com.

"It looks great on camera, but the moves are much harder in person than they look."

Sam revealed they love to workout together. "We run, we do a lot of yoga, we really challenge ourselves to do different types of exercises," Sam said.

"A lot of the yoga moves that she does I just can't do. She is a natural born athlete and she pushes herself, combining dancing along with various workouts. You just can't plateau when you're in shape. You really need to challenge yourself and change things up to maintain your fitness," he added.

While Britney and Sam love to hit the gym together, they also enjoy a variety of outdoor activities.

"Most of the activities we do involvement movement anyway. We go horseback riding, bicycling and now we are thinking about skydiving," Sam shared.

"Skydiving is a very active sport, so we are looking into getting into it. We do a lot of outdoor activities together. We really want to adventure and live the best quality of life that we can," he said.