After giving birth to her adorable twins, Max and Emme, Jennifer Lopez wants to lose lose the 50 pounds she gained and get back to her former shape.

She's already looking like she's dropped a few pounds. And she's contacted her Beverly Hills trainer, Gunnar Petersen, to really kick her back into shape.

Gunnar's already busy with Bruce Willis (3-4 times a week), Ben Affleck (4-6 times a week) and Penelope Cruz (she works out like crazy) at his private Beverly Hills gym.

But we asked him about going to Long Island to work with Jennifer, possibly in her reported new home gym that cost $50,000!

DR: So you're working with 'Jenny from the Block' again?

GP: Yeah. I'm heading out there (to Long Island) soon, within the month. I was in Long island with her last summer. We train all over the place, different facilities, on the track at the university, in the gym. She's cool to be around. She's someone that I enjoy working with because she puts the work in. She's got such a great outlook. She's balanced about it.

DR: Tell me about her motivation.

GP: She's not crazy exercise girl. She fits it into her day. But don't take that to mean she's not serious about it. She's very serious and very committed, but it's a part of her life, not her entire life. She's able to compartmentalize things so well. When she works out, she works out hard for sure. Get in, get out. That's how she does it.

DR: How many days a week?

GP: Anywhere from 2 to 6, depending on her schedule.

DR: How long do the training sessions go for?

GP: Depends where we are. If it's here in the gym it's an hour. Sometimes an hour and 15 minutes, one hour and 20 minutes, tops. I try to keep it around an hour, an hour and 15, including warm-up, cool down and stretch.

DR: Jennifer mentioned in "People" that she might do a triathalon.

GP: Yeah, well that's gonna change the training.

DR: How different will her workout be, having just given birth?

GP: We'll start with a bunch of flexibility work, functional training. Cardio will be at a moderate intensity. What she does in the gym should enhance everything she does outside of the gym. She's gotta have the strength/stamina to be a mum.

DR: So what is this about a $50,000 home gym that Jennifer's supposedly built? If she was going to splash out that much on a home gym, wouldn't she consult you about it?

GP: I don't know anything about that. But I would be a bit surprised (if she's built one). We'll see. And by the way, $50,000 doesn't get you much for a gym. Once you get the floor, and the mirrors and the audio, you're not left with a lot for equipment. She may have built one. I'll find out soon!

Photos: La Lopez already looks slender at the "Shine a Light" premiere in New York this week.
WireImage

Reporting: Sal Morgan