3. TRX Suspension Training  Because the Hotel Gym Is Dismal  Join This Craze if: You like the sound of yoga for Navy SEALS  The idea behind TRX is that with just two looped straps—as unembroidered a craze as there is—you can hit all the marks of a full-body workout, in limited space (in your living room, on the road) and time. Though TRX was designed for the military, the civilian version hardly approaches Seal training. But the versatility comes from dialing up the difficulty simply by moving your feet, adjusting the straps, or speeding through a circuit.  TRX started appearing in gyms in the mid- '00s, but the group sessions are only now picking up momentum. Most basic classes split the workout into thirds: legs, arms, core. Here are my three favorite TRX moves. From left: pool-less cannonball, scorpion hand-hop, and hang-glider push-up. (These aren't the real names, but they're easier to retain than the real ones.)—Daniel Riley  Intensity: 5   Price: Approx. $25 per session
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