Right after our first set of intervals, as I gasped for air amid encouragement from instructor Chris Layda, I thought well, gym cycling classes are toast. After more than a year in a development by a team of master instructors, SoulCycle launched its new SoulActivate class on Tuesday. And it is a bitch (but in a good way, of course).

Less about the sweaty playfulness and clubby choreography that put SoulCycle on the map, the hour-long, HIIT-style Activate class is the answer to critics who say Soul rides aren't scientifically optimal training for the cardiac system—a number of competing gyms and cycling studios have long focused on "smarter" programming that centers on increasing heart rate and strength training. Now, with an aggressive studio expansion and a following of veteran riders who could complete the traditional SoulCycle class in their sleep, the company is upping its game with the addition of this endurance-building class in studios throughout the Bay Area, New York, and Los Angeles.

The class begins as usual, with a warm-up song and a series of climbs and sprints with the brand's signature tap-back and push-up movements. At about minute 20, though, things took a more serious turn.

An extended weight-training session gave our legs a break but worked our arms using multiple, heavier weights than Soul's traditional rides. And then our instructor sprang it on us that we were in for some gnarly HIIT.

"This is how Olympic athletes train!" Layda shouted, pumping us up. "Pushing your heart rate as hard as you can, followed by real rest, is proven to make you a stronger rider, make you faster, make you better."

At what would have been halfway through a standard SoulCycle ride, we began a series of six intervals, turning up the resistance on our bikes until it felt like pedaling in quicksand. We spun as hard as we could for 20 seconds, then took a one-minute rest, our legs completely still, our chests heaving. After each run, Layda marked the number of sprints we'd completed on a whiteboard behind him; after the first, my legs felt thoroughly worked, my lungs like they were going to explode; after the sixth and final run, I felt like someone really should be handing me a medal.

After a brief reprieve sprinting on a lighter load, we rolled into a second set of intervals. I think I laughed as Layda announced what was coming—I'd barely finished that last set alive. (At this point in the class, a normal 45-minute ride would be over and I would be halfway down the street grabbing protein waffles at Project Juice.) But he wasn't joking, and we instead embarked on a series of eight sprints, 20 seconds each with just 10 seconds off. I honestly don't know how I made it through, but once we moved onto our final sprint song, I was high on my own oxygen and would do whatever he asked.

It's important to note that this class is definitely not for noobs: SoulCycle recommends riders take at least 10 standard classes before signing up for Activate. For experienced riders who already incorporate SoulCycle into a weekly fitness regime, the brand advises taking the new class about two times per week. For myself, I think once a week, as a way to really test and push my cardio system, is plenty ambitious.

// SoulActivate ($32 per 60-minute class) is currently available at SoulCycle's San Francisco studios in the Marina, SoMa, and Castro; in Larkspur; Walnut Creek; and Palo Alto. For more information and locations, go to soul-cycle.com.