Ask any boutique fitness connoisseur (including our three fitness editors) what the hardest workout in New York City is, and they’ll most likely tell you it’s SLT. Megaformer workouts are touted for their efficiency and results, and in a single 50-minute class, you’ll get cardio, strength, and flexibility training in one fell swoop. But for some cardio queens, the slow, controlled movements of the Pilates-inspired method aren’t fast-paced or sweaty enough. And so to make things even harder, founder Amanda Freeman decided to add treadmills into the mix.

SLT Tread, which will open in New York City in January, 2020, combines the slow cardio benefits of a megaformer workout with heart-spiking sprints, the motto being: “tread fast, tone slow.” And so, in what truly sounds like the most-challenging workout of all time, you’ll spend 25 minutes working your muscles to exhaustion on the megaformer, followed by 25 minutes doing high intensity intervals on the treadmill. “While the SLT workout on its own is the perfect combination of strength training, low-impact cardio, and Pilates, we often see clients interspersing their SLT workouts with high-impact cardio workouts such as running and cycling,” says SLT founder Amanda Freeman.

When most people think about “cardio,” their minds usually go to fast, sweaty workouts like running or spinning. But megaformer workouts, like the ones you’ve traditionally gotten at SLT, offer a different kind of cardio in which the slower you go the higher your heart rate spikes. With SLT Tread, you get the best of both all at the same time. “SLT Tread combines both slow and fast cardio into one all-encompassing, full-body workout,” says Freeman. “You get the targeted muscle-toning of SLT combined with the endorphin-boosting powers of running.” The result? A workout that puts every single muscle in your body to the test and will help you develop long, lean muscle in the process. In case there was any question, it will definitely leave you sweating.

SLT Tread’s first location will be located in The James Hotel (hello, wellness travel), and with only 20 spots on the roster, we have no doubt classes will fill up fast.

Here’s what happened when three Well+Good fitness editors tried three months worth of SLT. Plus, the *other* new megaformer workout people can’t stop talking about.