Don't be scared off by Pop Physique's butt-tastic website—beneath the LA-burnished facade of teeny-tiny, barely clad tushes is a workout that'll leave you sweaty and panting, but eventually able to dash up a broken BART escalator with far greater ease.

If you've done Pilates or Lotte Berk, you've already had a hint of the Pop Physique regimen created by Jennifer Williams, who launched her first studio in Silver Lake in 2008, after (among other things) a career as a professional ballet dancer and a seven year stint teaching Pilates in San Francisco. Since then, she's opened fifteen more locations in Southern California, as well as one in Russian Hill (2424 Polk Street) and, most recently, at 2744 Mission Street in, Williams says, the site of "an old Dollar Store."

At the Mission Studio's first class on August 1, a headset-wearing Williams led a packed studio through a series of movements that began as deceptively simple, swiftly descended into delightful agony, then ceased just as everyone in the room was ready to die. More a strength than flexibility workout, be ready for planks and pushups, arm work (those little pink weights you used to sneer at? Never again), then a long series at the barre (there's a sequence with a squishy pink ball between your knees that's especially glorious) that makes your grade school ballet class look like...grade school.

Challenging as it is, the workout is also definitely adaptable to multiple fitness levels, and the judgement level is low. Williams happily offered alterations to movements for those who were struggling, and, refreshingly, said "It's just exercise! You'll be OK!" when one student seemed frustrated by the challenge.

Class participants, who ranged from willowy to stockily athletic, clearly dug the hour-long class, hanging around to talk and indulge in a little opening-night cake after the session. Claire, a slender and graceful woman in her mid-20s, glowed with excitement as she said "I've done barre workouts before, but I really like this!"

And there's something strangely addictive about the routine. A day after class, long-dead parts of the body seemed to return to life, especially those in the gluteal region. And what does a resurrected ass want? Even more Pop Physique, apparently.

San Francisco Pop Physique studios are located at 2024 Polk Street in Russian Hill and at 2744 Mission Street in the Mission. New clients can purchase 30 days of unlimited classes for $100, or take a single class for $20.

GEAR

• Blessedly, class participants were not clad in the outfits you see in that Pop Physique-supplied photo above. Maybe they dress that way in LA, but not here—you'll be fine in close-fitting pants, tights, or shorts, and a tank top.
• Class participants must all wear socks with a grippy, non-slip rubber bottom (like those you see on hospital patients or your grandma). You can bring your own, or buy theirs for $11. 
• There are a lot of accessories! When you get to class, grab the studio-supplied mat, hand weights, strap, and pink ball. You'll be using them all.