Gunnar Peterson and Giulana Depandi at The 1st Annual 'Muscle Milk Light' Women's Fitness Retreat.

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Whether he's training Jennifer Lopez while she's on the road, or Angelina Jolie for her next movie, personal trainer Gunnar Peterson is up for the challenge. When training clients at his sprawling compound in LA, Gunnar takes a no-nonsense approach to fitness. You workout, period.

He's trained with everyone from boxer Mike Tyson to actor George Wendt (Cheers) and he never seems to slow down! But luckily we were able to grab him for a little Q&A (he was actually walking to a gym in Philly during the interview).

Gunnar tells how he keeps the stars in shape and how you can get the most out of your workout too!

Q: What is Jennifer Lopez' secret for staying in shape?

A: I would say her secret is being consistent and being driven. She is a goal-oriented person. She knows what it takes to get on top and to stay on top and she does it.

Q: How long do you work out with her on a typical day?

A: Anywhere from 60-90 minutes tops. It depends, like when we trained to do the movie "Enough," I introduced her to Wade Allen (see Getting Strong With Krav Maga) so she would do that and then work out with me, all at my facility. It's different every single day. We split the body up, two muscle groups a day. I will add something lower body everyday - not always heavy resistant - and I mix in interval stuff. I do a lot of peripheral heart action with her.

Q: What kinds of things can women do to get a body like Jennifer if they cannot afford a trainer?

A: The trainer does not have to be the key, it can be an added benefit. But they have to stay true to a program. They can't try every single fad that comes out every month in every magazine. I'm all about mixing it up, but they can't just do - as my grandmother would say - 'willy nilly,' trying this and trying that. For example during a cardiovascular workout, vary the degree of intensity, very the duration, vary the activity itself. Change intervals within the activity. Let's just take a stationary bike for example, do hard then slow, then hill, then no hill. It's all working your body differently and the more curve balls you throw it, the more its going to have to respond to or adapt to that, and the more it has to adapt the more it has to change.

Q: What is it like working with Angelina Jolie?

A: She is phenomenal as a person, she is phenomenal in the gym. She's tireless. She's a gamer, that's what I would call her; she's ready for anything. You can take her through hard exercises, hard rep counts, slow cadence, whatever it is she's just right there with you. She is so considerate and she's on time and she's there to do it. She's so strong. You'd be surprised - a girl her size - how strong she is.

Q: We all can't look like a star, so what should be a woman's workout goal?

A: I think you try to get across to them to be the best they can be and don't set unrealistic goals. If you are 5' 1", don't start saying, "well why don't I look like Claudia Schiffer?" It's not gonna happen. You have to look at the genetic hand you were dealt. Do you have long or short muscles or do you have more childbearing hips than 12-year-old boy hips? It's all about perception.

If I showed you a picture just of a behind, you couldn't tell whether it was big or small, but if I showed you a picture of the whole body from the back, you are looking at the width of the behind in relation to the shoulders, so it's all about perception.

So if you have genetically wide hips, maybe you need to work the shoulders a little more to make sure they have adequate breadth to them, then you'll be surprised at how much smaller the behind looks.

Q: What has been your most challenging client experience?

A: I would say the hardest are the people who are completely unaware or unwilling to see their own bad eating habits. Like the people who think, "Well I had chicken wings for lunch, what's wrong with that, it's chicken?" Well chicken wings are about as far away from chicken as a Hershey bar is from a cocoa bean.

So the people who are completely convinced they have been dealt this horrendous metabolism and it's like God's little trick on them and they are the victims - they take no responsibility - those are the hardest. You can also carry that over into their extracurricular activities, like drinking and/or drugs.

Q: What do you recommend as an exercise motivator?

A: I don't want to sound trite but it has to come from inside. You have to be doing this for yourself. If you are doing this for anybody other than yourself, you are destined to fail, and if not, you will build resentment toward that person. I can't tell you how many people's spouses bought them 10 sessions, and they were reluctant, going in only on their spouse's suggestion. Do it for you.