When the beat drops, so does your comfort zone.

Ten-stories atop 555 California is Bay Club's quaint, quiet, well-equipped fitness studio brimming with sweat-drenched bodies. And, while its two large group workout areas could each easily fit two dozen participants of The DROP, my drop-in would take place outside on the plaza to accommodate the larger-than-expected turnout. (The cool, fall bay breeze would be a welcome.)

"Welcome! I'm glad you finally found the class," bubbled Breann Mitchell, Bay Club's senior instructor. The DROP is the first of a new wave of Bay Club signature classes designed and taught exclusively by Mitchell, blending H.I.I.T (High Intensity Interval Training) and light yoga. "Grab a mat, some water, and your headphones."

Now the latter is where The DROP sets itself apart from other high-intensity workout classes I've ever taken: Each attendee is given a pair of LED headphones—provided by Sound OFF—to wear during the entire 45-minute workout; the instructor communicates through them over the music.

Between burpees, side-to-side lateral jumps, lunges, and countless high-knees, you'll feel muscle groups working that you may or may not know you anatomically possessed. Also, remember that towel that Mitchell suggested I grab? Next time, I may grab two because I needed them to wipe the copious amounts of sweat off my headphones (and forehead, and neck, and arms...).

Because the entire class is structured around the music's tempo-driven ups-and-downs, when the beat's mild and slow, you're expected to perform at around 80 percent. But, when the beat "drops"—hence the name of the class—you're expected to embrace that H.I.I.T mentality and give it your all. The EDM and heavy-bass playlist definitely helps push any self-established comfort zone.

"Alright you guys, good work! One more high-knee and down-switch to plank on the count of three." The encouragement pepped up my otherwise clumsy coordination. Needless to say, the 10-or-so minutes of yoga that followed were a welcome relief.

Pro Tips:

• Wear a good, grippy, stable pair of trainers
• Bring your own or use one of the provided mats
• Use the music to guide your pace and intensity
• Don't be afraid to do lighter forms of the exercises like knee push-ups or knee-downside planks

// 555 California St. (However, they have studios scattered throughout SF and the Bay Area), (Financial District), bayclubs.com