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Trying something new keeps you motivated to exercise. But which current fitness craze is worth your time, money, and energy? Real Simple asked health experts to weigh in.

TRX Suspension Trainer
The trend, explained: This piece of workout equipment was developed by a Navy SEAL as a way to stay fit in the field. The TRX, made up of nylon straps and handles, anchors over a door or some other stationary object and adjusts to different heights so you can do head-to-toe moves—push-ups, lunges, pull-ups—using your body weight. The equipment costs about $200 (trxtraining.com) and comes with how-to DVDs. Fans say that the TRX engages more muscles than the same moves performed on solid ground.

Expert opinion: “The main benefit of using the TRX is that it forces you to use your core to stabilize yourself,” says Scarsdale, N.Y.–based exercise physiologist Brad Schoenfeld, the author of Women's Home Workout Bible. For example, to do a plank pose on the ground, you only have to keep your body straight and lifted, using your abdominals for support. For a plank pose with the TRX, in which your ankles are held up by the nylon straps, you need to engage your chest, back, shoulders, and abdominals to ensure that you don’t fall over.

“The TRX is also convenient, because you can rig it up at home and adjust your positioning to increase or decrease the difficulty level,” says Schoenfeld.

The bottom line:  The TRX is worth it for almost anyone, especially for people who want a challenging way to exercise different muscle groups but may not want to sign up for a gym membership.
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High-Intensity Interval Training (HIIT)
The trend, explained: HIIT turns a regular cardio workout into a super-efficient one: You alternate between 20- to 30-second bursts of all-out effort and easier recovery periods. HIIT works with any cardio activity, including walking, running outdoors, and using the elliptical or stair-climber. The approach is said to strengthen the heart, the lungs, and large muscles, and devotees love it because of its purported fat-burning abilities. Plus, HIIT workouts are short—20 to 30 minutes on average. To try it: Start with a slow five-minute warm-up, then increase your pace (or resistance or incline) until you’re breathing heavily. Keep going for 30 seconds, then drop your pace, resistance, or incline down for two to four minutes; repeat three to four times. Because of the intensity, most experts recommend HIIT a maximum of three times a week.

Expert opinion: “HIIT is an excellent approach to cardio,” says Rachel Cosgrove, a personal trainer and the owner of Results Fitness, in Santa Clarita, Calif. “The harder your body works, even for short periods, the longer it takes to return to its normal resting state, which means your metabolism stays elevated—and you burn more calories—for up to 24 hours afterward.” And HIIT may be particularly effective at whittling fat from the belly and legs: A 2008 study in the International Journal of Obesity showed that women who did HIIT burned more abdominal and leg fat than did those who performed longer, moderate-intensity cardio.

The bottom line: Virtually anyone can benefit from HIIT, especially those looking to reduce fat.

Minimalist Running Shoes
The trend, explained: Some running enthusiasts believe that we naturally run best when we’re barefoot, and companies have developed shoes to mimic this, since bare feet and hot asphalt don’t mix. The first, admittedly odd, models had separate spaces for each toe—think gloves for your feet. Since then “barefoot” shoes have evolved. The newer versions look more like regular running shoes but have little cushioning. Many major brands, including New Balance and Saucony, carry minimalist sneakers. Advocates like their light weight and the way they allow you to feel your feet striking the road better than heavier traditional running shoes do. Some also believe that wearing minimalist shoes can strengthen foot and ankle muscles.

Expert opinion: “Very few people have a perfect running gait. Many people overpronate [roll in], supinate [roll out], or have fallen arches,” says Dr. Nadya Swedan, a physiatrist in New York City. “Minimalist shoes don’t have the support to compensate for these problems, so using them may lead to injuries, such as plantar fasciitis and Achilles tendonitis.”

The bottom line: Tread carefully. If you’re certain you have a neutral gait—that is, your feet don’t roll in or out with each step—give them a try. (Not sure if you have a neutral gait? Time yourself standing on one foot. If you can do so for one minute without wobbling, you’re probably OK.) For over- or underpronators who still want to try minimalist running shoes, consider hybrid models from Brooks (pictured) or Asics. They’re flatter and lighter than traditional running shoes but offer more support than typical minimalist versions do. Your best bet: Go to a specialty running store, where they can evaluate your gait and suggest the right shoe for you—minimalist or not.

Digital Body Monitors
The trend, explained: “Activity managers,” such as the Fitbit (fitbit.com), the BodyMedia FIT (bodymedia.com), and the Bodybugg (bodybugg.com), are worn on an arm or clipped to a belt. They use ultrasensitive movement monitors to track steps, distance, calories burned, time spent exercising, and even tossing and turning at night. (You can wear them 24/7.)

They can sync with a computer or a smartphone, allowing you to log meals to compare calories consumed with calories burned and chart workout stats over time.

Expert opinion: “These devices are good for accountability, because you can see exactly where you stand in relation to your goals,” says Anderson. The BodyMedia FIT is recognized as a medical device by the U.S. Food and Drug Administration, and a 2011 study published in the journal Obesity showed that dieters who used it lost more weight than those who didn’t.

The bottom line: They’re not essential. But if you’re a goal-oriented person or like instant feedback, they can be a fun tool in your health-and-fitness arsenal.

CrossFit Workouts
The trend, explained: Think of CrossFit as a supercharged boot camp that combines high-intensity cardio and resistance training. Conducted in a class setting at CrossFit gyms, a typical routine might involve swinging kettlebells, flipping tractor tires (yep, real ones), throwing weighted balls against a wall, and doing body-weight moves, such as squats (with or without dumbbells) and push-ups. Classes are usually small—5 to 20 people—and last from 20 minutes to an hour. The workout is different every time, so you don’t get bored, and fans report rapid weight loss and muscle toning.

Expert opinion: “CrossFit can be an intense workout,” says Los Angeles trainer Kristin Anderson. “You’re focusing on endurance, agility, power, and strength in one session, and all require different things from your muscles.” While you work at your own pace, the group atmosphere adds a feeling of friendly competition. However, some experts worry that this can lead to injury, especially if a person pushes herself too hard to keep up with the group.

The bottom line: If you’re already in great shape, CrossFit is a challenging way to get even fitter. Beginners should take it slow, though. Most CrossFit gyms require newbies to complete a fundamentals course before joining regular classes.

Myofascial Release Therapy
The trend, explained: This technical-sounding technique is actually quite simple. It involves using an inexpensive prop, like a Muscle Therapy foam roller or a Myo-Therapy ball, to work the kinks out of achy muscles. (In a pinch, tennis balls work, too.) Myofascial release is said to manipulate the fasciae, thin membranes that cover each muscle, which may alleviate knots and soreness better than massaging muscles alone does. To try it, place your prop of choice on the floor or against a wall and lean on it so it’s under the tender spot. It should feel slightly uncomfortable. Hold for 30 to 45 seconds. To increase the effect, gently roll the prop back and forth on the area.

Expert opinion: “When it’s healthy, the fascia over a muscle is like a pillowcase that slides easily over a pillow,” says John R. Martinez, a doctor of physical therapy in New York City. “But when you have injuries or chronic inflammation, the fascia can bind onto the muscle and restrict its movement, which causes discomfort.” Myofascial release therapy helps “unstick” the fascia, he says.

The bottom line: Myofascial release therapy can be helpful for any sore muscle. It’s especially good for targeting hard-to-massage parts, like the quadriceps and the hamstrings, and trainers often suggest using it after workouts to help speed recovery.