Some group fitness classes definitely make us work harder than we would on our own, but in others, we barely break a sweat. Thankfully MetCon3, an interval-based, total-body class offered at Equinox gyms, fell into the first group: Afterward we were soaked in sweat and feeling a lot stronger (OK, and more sore) than when we walked in.

The workout is based on metabolic conditioning, a type of interval training designed to improve the storage and delivery of energy by engaging the body’s metabolic systems. Studies show this type of high-intensity interval-style training can boost aerboic fitness as much as longer cardio sessions and improve muscular endurance and increase metabolism more than cardio can by itself.