From spinning to boot camp to sprints, Matt Warshauer prided himself on being fit enough to handle any cardio challenge thrown at him. Then the 31-year-old Los Angeles television writer tried a private training session on the VersaClimber (that oft-overlooked, oft-unused monolithic piece of equipment) with celebrity trainer Jason Walsh, who's known for sculpting the bodies of Justin Timberlake, Jessica Biel, Ben Affleck, and Matt Damon.

"It was intense," Warshauer says of the workout, which engages both the upper and the lower body in a simulated climb that burns up to 16 calories a minute (more than the average for running, cycling, rowing, and swimming). "I was shocked at how fast my heart rate went up. Within minutes, I was really sweating." After five weeks of adding a couple of climbs to his regular strength regimen, the six-foot-one distance runner lost 12 pounds—with no change to his diet.

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Make the Most of Your Workout
Jason Walsh shares tips on what to eat and drink and how to balance your routine.

Walsh (seen here with Justin Timberlake) recommends running
on days spent off the VersaClimber.

1 / Fuel yourself with carbs (oatmeal and PB&J are good) an hour or two before exercising to prevent crashing.

2 / People often push themselves too hard at the start. Warm up with five minutes on the machine at a slow, steady pace, followed by a stretch before your workout.

3 / Make it through any intense cardio session by hydrating with a beverage that has electrolytes and amino acids, like Surge Workout Fuel by Biotest.

4 / To balance out the single-plane motion of the VersaClimber, add in rotational and lateral strength movements (like wood chops) three or four days a week.

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"Everyone I train uses it," Walsh says, just as Justin Theroux and Amy Adams arrive to do their time on the VersaClimber. Walsh is so convinced of the machine's effectiveness he's bringing his regimen to the masses by launching a high-intensity climbing class at his new Rise Nation studio in West Hollywood, with plans for a New York outpost to follow soon. If he has his way, climbing will rival indoor cycling and rowing as a star of the group-fitness scene.

It's difficult to picture how the classes will play out until Walsh walks you through the paces. As with spinning, the tempo and cadence fluctuate to keep tough sessions doable—warm-ups are set to slow R&B jams, short sprints to upbeat house music. Walsh leads the group through multiple intervals and movement patterns, like staccato three-count climb-and-holds and single-sided spurts, and he varies resistance levels (changed via a knob, à la a stationary bike) to work the upper and the lower body separately. Advanced classes will expand from 30 to 45 minutes, with 15 minutes of flow yoga sandwiched in. To be added to the schedule soon: one that peppers core-focused strength training throughout.

The question remains as to how widely Walsh's vision will catch on, considering it revolves around a somewhat intimidating-looking machine that rarely has workout devotees waiting in line the way runners will for a turn on the treadmill. Yet having an instructor as a guide might be the key to boosting fitness acolytes' familiarity with the VersaClimber.

"The last thing most gymgoers want to do when presented with an unfamiliar piece of equipment like this is attempt to figure it out with everyone watching," says Jacque Ratliff, an exercise physiologist and education specialist for the American Council on Exercise. Still, it's worth trying: Ratliff notes that the vertical stance is easier on the lower back than a bike, and because there's no impact (your feet are strapped on to the steps), it's less jarring to the joints than a treadmill. In fact, the idea for group climbing came to Walsh after he witnessed clients injure themselves improperly executing moves in CrossFit and on spin bikes.

"People want to belong to exercise communities," Walsh says. "They bring their friends, compete against each other, and go for smoothies after. It's a healthy way to socialize. But their bodies are not getting the right benefits." Not only is there less risk of injury, but because you're strapped in, there's no coasting (unless you want to embarrassingly dismount the machine mid-class). As Warshauer puts it, when it comes to the VersaClimber, "you can't cheat yourself."