Sometime between the third and fourth set on our Versaclimber, as we mopped the sweat from our brow for the umpteenth time, we realized the crucial truth about the Bay Club's new Ignite HIIT class:

This 50-minute fitness excursion is not for workout noobs and yoga princesses.

Combining the slow burn of weight training with the metabolic immediacy of cardio, high intensity interval training (HIIT) is the rage these days (we reported from SoulCycle's version of the class back in February). So when we caught wind that The Bay Club was launching a class that incorporates stationary rowing, climbing, and running with light weight training to work every muscle imaginable, we thought fit to check it out for ourselves.

Created by Breann Mitchell, leader of disco yoga sessions and also creator of the club's Signature Class, Ignite ebbs and flows over six rounds of calorie-burning exercises, in a blue-lit studio space, with a focus on interval cardio and strength training. Each set incorporates 45-second "ignitions," followed by 15-second breaks (savor them).

But before we dove in, we were first guided through a three-minute warm-up—this is your chance to prepare your body and to fortify your will for the limit-pushing workout to come. After selecting either five-, 10-, or 15-pound weights, we began performing a litany of deep lunges and other dynamic, weighted motions. (If you're at all familiar with kettlebell workouts, you've likely already done these in some variation.) Then, after we slid the weights beneath our "escape deck—which looks something like an aerobic stepping block—we ventured over to the Versaclimber.

"Keep those motions tight and at a good pace," our instructor shouted above the remixed Diplo track. "Five more seconds, give it all you got!" And according to our underarms, we did.

The following sets were tackled with similar intensity: The muscle-burning lunges, the overhead weight lifts, the uphill treadmill climbs, and the nearly minute-long planks tested our waning stamina, sending us teetering toward our breaking point. And then came the final five-minute cardio push on the Concept Two Rowers—and then came the hot acidic feel of vomit welling up in the back of our throats.

But we rowed with the purpose of Olympians toward the finish line, until our biceps and quads couldn't exert another ounce of kinetic energy. And just when we thought we might have to throw in our white, sweat-soaked towel, the final countdown began: "Three, two, one—that's it, guys! You did it!" And so we fell flat on our backs, desperate to catch our breath—this was not the time to play it cool. Our muscles were on fire.

// IGNITE will launch the week of July 30^th, and classes will be free to Bay Club members or guests with a three-day trial club pass at the San Francisco club (150 Greenwich St.); look for classes at the club's other locations later this year. For more information, go to bayclubs.com.