Starting March 30, Alycea Ungaro’s Real Pilates will be offering STS (suspension training system) classes. STS is also known as TRX (total resistance exercise), and despite all the acronyms, suspension training doesn’t involve much more than an adjustable seatbelt-like strap. “It was invented by Navy SEALS stationed somewhere hideous,” says Ungaro. “They were wondering how they could stay in shape when all they had was parachute webbing.” They tied it to a tree, and suspension training was born.

Ungaro first tried suspension training upstate, and she loved it immediately. “It’s like Pilates on steroids!” she says. “It’s an amazing home workout system, but you have to know what you’re doing.” She demonstrates how you can do all sorts of exercises with the straps, depending on whether you’re facing forward or backward, putting your hands in the handles or your feet. You have to work hard just to keep the straps from moving, and even a slight shift in angle—much easier to do with STS than with a rigid system—can make for an incredibly challenging workout. “Your muscles will be shaking,” says Ungaro. (Lily, who works at Real Pilates and agreed to pose for a photo, clearly found it tough going.)

When Ungaro brought STS to her studio, her trainers felt about it the way she did. “They were like, ‘We can use this in Pilates!’ It’s great for core training—lower back, abdominal—which is exactly what Pilates is all about.” Real Pilates will offer two classes: Pilates STS and Pure STS. The classes are 45 minutes, with room for 10 participants. A single class is $27; 10-packs are $235; 20-packs are $420. Initially, a handful of classes will be free (call and ask which ones).

Alycea Ungaro’s Real Pilates is at 177 Duane (bet. Hudson and Greenwich); 212-625-0777, realpilatesnyc.com.