THESE ONE- HOUR CLASSES are built around improving cardio endurance, flexibility, core strength, agility and balance on four wheels. You don’t need to be a whiz on skates to partake in Rollerfit. The only prerequisite is the ability to laugh at yourself once you’ve taken your upteenth tumble.we work our way through basic drills, core exercises and stopping (though skating into the gym’s walls is a good fallback plan). I start sweating at the get-go, moving muscles I never knew existed and high-fiving fellow skaters who’ve also taken falls. Even though I’ve spent the majority of the class on my backside, I make plans to return the following week, mentally preparing for the incoming bruises, which I’ll no doubt be showing off, gleefully, to anyone who asks.