Here's how 9 celebrities work out, and what the science says about their fitness plans

The scoop: To get ridiculously ripped to play a boxer in the new Rocky movie "Creed," Jordan worked with personal trainer Corey Calliet. His workouts included 45-60 minutes of cardio, boxing training, and an intense regimen of sit-ups, push-ups, squats, and other exercises, according to Men's Journal. (See the full workout here.) He paired these workouts with a strict, high-protein diet to build muscle.

Should you do it? Probably not. Unless you're planning to star in a boxing movie, you don't need to follow such an extreme workout plan. The cardio workouts and high-intensity exercises may be good for you, but boxing and the head injuries it causes are linked with a host of problems, including chronic traumatic brain injury, which in the long term can lead to punch-drunk syndrome, or chronic traumatic encephalopathy, a tragic brain disorder also found in football players.

The scoop: The reality TV star is just one of many celebrity devotees of Barry's Bootcamp, a popular fitness studio that debuted in California in 1998 and now has 18 locations around the US, Norway, and England. The night-club-esque gym offers hour-long workouts that include 25-30 minutes of interval cardiovascular treadmill routines and 25-30 minutes of strength training with free weights, resistance bands, medicine balls, and other equipment.

Should you do it? Perhaps. One of our reporters tried a week of Barry's workouts in Manhattan, and concluded that the classes helped her build endurance and shave more than a minute off her mile time. Also, studies show that interval training may have many of the same benefits as longer workouts. But it ain't cheap: though prices vary, a single class at the Chelsea location will set you back $34.

The scoop: To get ready for the role of Batman, the Oscar-winning actor and director followed two workouts, according to PopWorkouts: First he followed a fat-burning workout to get lean, and followed it with a muscle-building workout to bulk up.

Should you do it: If you want to burn fat, experts say that weight-lifting, or resistance training, may be a great way to do it. If you take into account the length of the workout, it has the same fat-burning effects as cardio, and you continue to burn fat afterwards in a process called excess post-exercise oxygen consumption. Of course, diet plays a big (possibly bigger) role in weight loss, too.

As for muscle-building, weight training is key, but it's also important to eat protein to help build muscle mass. One expert recommends consuming about 20 grams of protein, or about one scoop of protein powder, right after a workout.

The scoop: According to Shape, the pop star singer of "Hips Don't Lie" trains with fitness coach Anna Kaiser, owner of AKT InMotion Studio in New York City. Her routine entails lunges, leg pulses, squats, and plank-push-ups. The singer started with half an hour each morning and evening, and gradually worked up to an hour.

Should you do it? Can't hurt. Having a personal trainer can keep you accountable. And short, high-intensity exercises like squats and planks have been shown to have many of the same benefits as longer workouts. But two hours of exercise a day may not be everyone's cup of tea...

The scoop: He's not called "the Rock" for nothing. To keep himself in peak condition, the actor and part-time professional wrestler gets in a full workout 6 days a week, including both cardio and weight-lifting, according to Bodybuilding.com. He usually does 30-50 minutes on the elliptical or goes for a run in the AM. Then, he hits the gym for some "clangin' and bangin," as he calls it.

Should you do it? If you're planning to star in some action movies, this probably isn't a bad way to go. As mentioned previously, research suggests that running can decrease your risk of death and heart disease, and weight-lifting is a great way to burn fat and build muscle.

The scoop: The Oscar-winning actress doesn't look great by doing nothing. Everyday Health reports that Berry got in shape after giving birth to her daughter by working out 5 days a week for an hour, doing a combo of ab and leg exercises, elliptical, kickboxing, and either stairs or hill-climbing.

Should you do it? Kickboxing can be a great workout to reduce stress and burn calories. A typical kickboxing workout can burn up to 450 calories an hour and may help improve flexibility, balance, and stamina, according to Everyday Health. And as mentioned above, high-intensity exercise (like stair-climbing) can give you the same benefits as longer, less intense workouts.

The scoop: According to Everyday Health, Aniston keeps fit with yoga. Shape reports that Aniston works with yoga teacher and friend Mandy Ingber, whose yogalosophy program pairs yoga with toning exercises.

Should you do it? Sure! A growing body of research suggests that yoga is good for your mental and physical health. One 2010 review of 81 studies published in the Journal of Alternative and Complementary Medicine found that yoga was equal to or better than other forms of exercise at improving health in almost every way measured (interestingly, except for physical fitness). But other studies suggest that practicing yoga for at least 10 weeks can improve lung function, which is related to fitness.

The scoop: Whether it was bulking up for "Jarhead" or slimming down for "Nightcrawler," few actors have gone through so many physical transformations for their roles as Gyllenhaal. To get ready for last summer's "Southpaw," Gyllenhaal trained like a boxer for 6 hours a day for 5 months, according to Bodybuilding.com: He'd start with an 8-mile run each morning, followed by sparring, a short break, and a bodyweight and core workout.

Should you do it? If you're looking for an intense workout! Running has been shown to improve aerobic fitness, improve heart function, and is good for your metabolism. And core training is an important part of physical fitness — strengthening abdominal muscles, improving balance, and improving overall fitness. But you might want to skip the boxing ring if you want to avoid the risk of serious trauma...