I am one of those people who uses their jeans as an exercise barometer. When my denim starts feeling a little too tight, I know it’s time to start working out. But, as with everyone, finding time to fit a sweat session in isn't easy. The mere thought of waking up before the sun rises to do a pre-work run almost makes me laugh. And when I come home from my long commute, I just want to hit the sack — not the gym.

That’s why I turned to 12th Street Gym (204 S. 12th St., 215-985-4092, 12streetgym.com) to give me a little workout discipline. The fitness center’s new Ranger Workout was just what I needed to get me back on track.

Sgt. Nate Griffin, a retired U.S. Army instructor (for real!) started off the class with simple, army-inspired aerobic exercises. We marched, stretched and balanced our way through the first part of our workout. Then things got more challenging. I channeled Demi Moore and her rock-hard determination in G.I. Jane as we pumped iron while balancing on one foot; crunched our abs nonstop for two whole minutes; and then upped our heart rate with Griffin’s version of a jumping jack (which was a lot harder than I remember from high-school gym, where I half-heartedly swung my arms over my head and jumped less than an inch off the ground). It got so intense that if there had a been a bell, I would have definitely rung out.

But before I knew it, the drills were over and I was lying on a yoga mat, meditating and letting my sore limbs relax. (A needed break from all things Army!) I closed my eyes and listened to Griffin’s inspirational talk: “Don’t make excuses,” he says. “Make it happen.” And although the exercises made my muscles ache, I left feeling like I could do anything I set my mind to.

If you’ve tried a new class in or around Philly, tell us about it! We’re always looking for new ways to tone up and trim down.