By Emily Feimster It takes a lot more than just sweatin' to the oldies if you want to make it in Hollywood. As Tinseltown has upped its demands on celebrities staying it shape, the gym has become a sort of sanctuary where there's no rest for the weary. After all, looking good for the camera doesn't come easy. But if it means keeping their $10 million paychecks, you better believe these famous folks aren't complaining. So join us as we take a look at how they keep those rock hard bodies!

Oh how we've often admired Usher's genes (not jeans, though we certainly aren't complaining about those). When working out, the singer kicks off his three-hour training sessions with 20 minutes of meditation and 30 minutes of "static stretching." He then spends 90 minutes working out on cardiovascular machines, 10 minutes concentrating on his famous abs, which includes 1,000 crunches, and he always tops it off with a 15-minute steam before taking a cold shower. Yeah!

Following in his footsteps is the very health conscious Jessica Alba, who says her routine includes Tae Bo, weights, cardio, and occasionally golf. "I work out anyway just because it's healthy to work out and women have health problems, especially in my family," she notes. As for the other famous Jessica - Simpson that is - her workout includes two hours a day of squats and lunges. "I have a white-girl booty, so I'm doing all my squats to lift it a little bit and get some junk in my trunk," says Simpson. Hey, so far so good!

However, it's her famous ex-hubby, Nick Lachey, who seems overly obsessed with hitting the gym. The often-shirtless hunk of man, who studied Sports Medicine at Miami University, doesn't go a day without pumping iron. He's even doing infomercials alongside Hollywood hottie Brooke Burke for personal trainer Gunnar Peterson's new workout called Core Secrets.

The famous trainer has been behind the behinds of some of Hollywood's biggest A-list stars like Jennifer Lopez, who has been going to Gunnar for more than seven years. During their sessions, she works out her arms, chest, back, and abs. "There is not one bad body part on her. She is truly one of a kind," gushed Gunnar of the star, who reportedly also takes yoga classes.

Some of his other famous clientele includes former ballet dancer Penelope Cruz, whose workout regimen includes full-body strength training and cardiovascular exercise, and Sylvester Stallone, who focuses on strength training and plyometric exercises for the upper body. Of course we can't leave out Angelina Jolie. In fact, Gunnar traveled to London with her during the filming of "Tomb Raider: The Cradle of Life" where he designed a workout regimen which included many hours on a climbing wall as well as kickboxing, bungee ballet, and scuba diving.

Ah, yes, there are plenty of other celebs, who hit the gym hardcore when getting ready for a flick. New dad Ben Affleck says that he does three hours in the gym six days a week of weights and cardio. Nicolas Cage claims to have done a similar regimen where he got to 3% body fat! Wow! Who knew he had so much in common with Nicole Richie?

While preparing for "Spider-Man," Tobey Maguire says, "My workout is three to four hours a day, six days a week. It's a lot." Um, yeah. Then there's Drew Barrymore, who got in tip-top shape for "Charlie's Angels" by doing squats, lunges, and pushups with a clap.

Some of Hollywood's other fitness freaks include Jake Gyllenhaal, who is an avid surfer, and can often be spotted running with Ryan Phillippe at a track in Los Angeles. Gwyneth Paltrow practices yoga for 90 minutes a day. Sandra Bullock prefers to salsa dance her calories away. Helen Hunt and Brooke Shields take spin classes. And Carmen Electra takes off clothes (and pounds!) in Crunch's Cardio Strip class, a cardio and sculpting workout that teaches striptease moves. Now that's what we call an exercise worth learning!

So how is it that these famous folks seem to have so much time to obsess over their bodies? According to Gunnar, it's because they have made fitness a regular part of their lives. Though they may not always enjoy exercising, each of them is committed to getting it done. "It should be as unthinkable to skip your workout as it is to skip brushing your teeth," he has said. Point well taken.

Whew, with all this talk of working out, it has made me hungry. Anybody know where I can get a Big Mac? Oh, wait.