Albi Skenderi loves nothing more than challenging his body. After hanging up his racing spikes, the 27-year-old former collegiate champion in the 110-meter hurdles dove headfirst into the intense Olympic lifting circuits of CrossFit—hitting the box for up to two hours, at least five days a week. So when the owner of his gym, CrossFit Hell's Kitchen in New York City, dared Skenderi to take a turn on a Schwinn Airdyne, he didn't think twice about it. What could be tough about an eighties-era stationary bike with poles like an elliptical and a giant fan for a front wheel? When he had to stop after just one minute of intense pedaling, Skenderi realized he had found the ultimate cardio workout.

Fan Favorites: 3 Workouts to try
Next time you spot an available Airdyne, test your fitness (and willpower) with one of these routines, recommended by Michael Blevins of Gym Jones in Salt Lake City.

1. The Finisher
Add this to the end of your normal weight-lifting session for increased fat burn and peak power. Aim to finish in the same amount of time each round—don't slow down as you progress.
Time: Approximately 20 minutes
Plan: Pedal and pump your arms as hard as you can until you burn 20 calories. (Shoot for under a minute.) Rest for 2 minutes. That's 1 round. Do 7 rounds.

2. One Minute, All-Out
Do this every month to test your power-endurance level. Not completely wiped out afterward? You didn't go hard enough.
Time: 1 minute
Plan: Pedal for 1 minute, burning as many calories as possible in that time frame. The record at Gym Jones is 87.

3. Airdyne to Hell
After a light lifting or body-weight workout, use this interval scheme to burn serious calories and bolster your cardio.
Time: 12 minutes (less is better)
Plan: Ride until you burn 50 calories (do this as quickly as possible, aiming for 1 calorie per second). Rest for the length of time it took to do so. Repeat, this time burning 40 calories. Continue, burning 30, then 20, then 10, resting as long as the previous period of effort.



"It was one of the toughest things I've done," says Skenderi, now a hedge-fund analyst. "It took me 10 minutes to recover from that one minute." The bike—which you power by both pedaling and pushing and pulling a set of handlebars—was invented more than 30 years ago but is experiencing a resurgence among hard-core cardio aficionados. The Airdyne isn't designed for long, leisurely sessions, like a treadmill or a stair-climber—it just feels like an eternity when you're on one. But while time may pass slowly, the calories burn fast—Skenderi shed 50 in his first 60-second ride, and top trainers can burn upwards of 75 a minute.

No Easy Way Out
Unlike the average spin bike, with its flywheel and adjustable magnetic-resistance system, the Airdyne uses a fan, which builds wind resistance exponentially. "The harder you pedal, the harder it becomes," says Michael Blevins, a trainer at Gym Jones, a world-renowned fitness facility in Salt Lake City where the Airdyne is included in many group workouts and private training sessions. The steep curve maintains tension in your muscles—eliminating the opportunity to quickly recover and flush lactic acid (what makes muscles burn), as your body does during intervals on a stationary bike, a treadmill, or a rowing machine. Instead, the Airdyne fights back. "It's a real character builder," Blevins says. "It can quickly put you in a very uncomfortable place if you go hard enough. But that's what triggers real results."

"You're forced to work harder than you do on most cardio machines," says Brad Schoenfeld, Ph.D., a professor of exercise science at Lehman College in New York City, referring to the upper-body work that leaves your whole system flooded with lactic acid. "That boosts your metabolism for hours and causes your body to increase enzymatic activity and release more fat-burning hormones."

Numbers Don't Lie
Skenderi says he was in good shape before he started doing Airdyne workouts (some just a minute long, others up to 20), but that the machine helped him reach otherwise unattainable goals. "I was able to knock a couple percentage points off my body fat—I'm now below 10 percent," he says.

There is one caveat: Blevins—whose job at Gym Jones is to prepare actors for must-be-ripped roles, including Henry Cavill for Man of Steel—cautions that because the Airdyne causes such a pronounced spike in your metabolism, it can make you ravenous: "You have to lock down your diet to improve body composition." But if you're able to control your consumption while answering the Airdyne's challenge, the payoffs can be huge. "I have a love-hate relationship with the thing," Skenderi says. "I hate how difficult the workouts are, but I love what it's done for my body."