We're here with celebrity trainer, harley pasternak. We're sharing secrets to training the stars. Boy, you trained some of the most fit out there. We're talking rihanna, kim kardashian, katy perry.... See More
We're here with celebrity trainer, harley pasternak. We're sharing secrets to training the stars. Boy, you trained some of the most fit out there. We're talking rihanna, kim kardashian, katy perry. And now, you. You're going to teach us how to have an all-star body. You don't need my help. Come on. We're jumpstarting our january. We're starting with the legs. Katy perry has legs that are just so toned. She is. We can do it playing a video game. We have a video game. Harley pasternak, hollywood workout. You can do it at home. And under 30 bucks, you get me. You get me telling you how to do the exercises. The avatar of me, with the sarcasm. Oh, good. And notice, I have no hair in the game. And I'm shorter than josh again. You could have taken liberties. But you didn't. And you say this is fun. But it's really work. It really does. And before, we were doing the jump squats. And all the fitness models were complaining. Their butts and thighs were hurting from 30 seconds. We have demos. First thing, the sumo squat. It is a simple movement. It works the thighs and the butts. We have laundry detergent. Grocery bags. You don't need equipment. You can do this. It's a great exercise for toning lower body. Or if you want to use weight, how much do you recommend? Try with a five-pound dumbbell and work your way up. Her weight is between the arch and her heels. She's keeping her body upright, looking forward the whole time. Just like a sumo, squatting down before your heels. Josh, go for it. Let's look at the abs. And this is compromising. This sounds strange. But the key to an amazing midsection is a strong lower back. It opens your midsection and makes it appear -- the core. The core, exactly. This is called an alternating superman. Now, we're alternating. And this not only works the body going up and down, but also cross-plain. And this is something that megan fox has done. Absolutely. Especially after becoming a mom and giving birth. You want to open that core up and strengthen the lower back. Will this alleviate the lower back pain that some of us mom experience after childbirth? Big-time. Great exercise to do. I'm in. Tell me about the next one. This is a stiff leg dead lift. Really important for toning the thighs where the butt and the thighs meet. You don't need equipment. Pushing your head up. And notice she has a great arch in her lower back. The back never rounds. It stays upright. This is for the bootee? This is for the bootee. It doesn't look that hard. And clients like rihanna and kim do this with you. Now, we can do it at home with the video game or use tse demonstrations. That's right. A lot odifferent muscle groups. Working the shoulders. We can't all throw the ironman suit on, like robert downey jr. We have something. This is an amazing tricep exercise. No equipment whatsoever. It's like a push-up, accept you're leaving your lower body on the ground. And driving up through the heels of the palm, right through the tricep through the back of the arm. She has incredibly strong arms. Great movement to do. You can do this anywhere, watching "gma" in the morning. I want to get one viewer question superquick. This is stacia, from pennsylvania. Can you suggest something to get the most out of a walk with a 3-year-old in tow? Yes. Get a pedometer. A pedometer is a great tool. And make sure you're taking 10,000 steps a day. Get a comfortable pair of shoes. Tell us the name of the game. Harley pasternak. Thank you so much. Harley has more tips online. Go to goodmorningamerica.Com on yahoo! And you'll see harley's answers to more of our fitness
This transcript has been automatically generated and may not be 100% accurate.