He warned us. Josh Newman, co-founder and co-owner of CrossFit NYC, instructed the group of about 20 students who showed up to the beginners' CrossFit class this weekend to use our gluteal muscles, and not just our leg muscles, to get into a squat position. Otherwise, we'd wake up the following day feeling sore and sorry. Clearly, I was not one of the wayward students, and the soreness I encountered stepping out of bed the next morning was only a sign of sympathy for my less attentive classmates. Squats were part of a series of exercises that introduced the class to some CrossFit basics (see us in action here). According to Newman, CrossFit is characterized by variety, functionality, and intensity. Workouts typically involve short, intense bursts of exercise designed to prepare the body for real-life situations, whether it's rock climbing, moving heavy furniture, or just walking the dog. In this week's class, students also practiced push-ups, L-sits, and a stretch that promotes flexibility (according to Newman, the only stretch you’ll ever need to do). Newman showed us the correct positioning for squats and push-ups and emphasized the importance of proper form to avoid muscle strains and other injuries. Some CrossFit exercises, like push-ups, don't involve any equipment beside the human body. CrossFit stretches can be similarly equipment-free, and some stretches require nothing more than a wall. A few exercises we tried this weekend featured wall balls (they feel like softer medicine balls) and parallettes (two bars that stand low to the ground, a type of gymnastics equipment). L-sits, a core exercise that's surprisingly difficult , involved crouching down between the parallettes and using them to lift yourself off the floor, extending both legs. (CrossFit's not a way to impress people by breezing through a workout. It's hard to suppress a grin in a roomful of adults panting and grunting as they struggle to lift their legs a few inches off the ground.) In the past few years, CrossFit gyms have sprouted up all over the country as the protocol has become increasingly popular. Check out CrossFit NYC's website here and follow them on Facebook and Twitter.