Workout Tryout: The AlterG

The AlterG anti-gravity treadmill is a lot like a spaceship: high-tech, high-flying and high-priced ($35,000 to start). In other words, an investment that few mere mortals are willing or able to make. But since the machines were introduced in 2005, a handful of gyms and fitness studios have recognized how valuable they can be to injured, rehabilitating or—like me—pregnant runners and athletes, and have bought in. I got my weightless running on at New York’s Body Space Fitness, which brought its AlterG on board in June. Here’s what I learned.

How It Works

A technology called positive air-pressure control—based, unsurprisingly, on NASA research—allows users to manipulate their bodyweight while preserving correct form. You’ll wear what amount to neoprene compression shorts attached to a skirt that zips into a plastic compartment that envelops the treadmill. Once secured, a tube around your middle inflates and deflates according to the percentage of body weight—from 20 to 100 percent, in 1 percent increments—you choose to, as AlterG says, “unweight.”

How It Feels

I was 28 weeks pregnant (pictured above) when I gave the treadmill a spin and it felt nothing short of revolutionary. Intervals felt possible! Going fast was an actual option! The sensation is a bit like floating at first; my feet rose off the belt a touch as the percentage of weight assist increased. The inflated tube around my middle made me feel like I was running with a kiddie bounce house strapped to me—a little jostly from side-to-side—but I adjusted quickly and the overall sensation was spectacular. I didn’t experience any of the heavy downward pull on my belly that regular running caused, though the setup did exert some pressure on the bottom of my bump. All was forgotten, though, when we upped the speed and tested a few different levels of weightlessness.

Keep In Mind

To mirror a “real” run as closely as possible, Gabe Griego, AlterG’s vice president of marketing and clinical, recommends running roughly .6 miles per hour faster than your normal pace for every 10 percent you unweight. You could also wear a heart rate monitor or watch your perceived rate of exertion to stay in your target zones. But you’ll probably just want to run for the sake of running in the beginning—it feels that good.

Body Space Fitness; single 30-minute AlterG sessions begin at $25 (5 sessions, $99; 10 sessions, $189); 47 W. 14th St.; 646-684-4912; bodyspacefitness.com.