To an outsider looking in, a room full of women spinning and marching across the dance floor in unison, hips and hands cutting through the air while chanting "Who runs the world? GIRLS!," may seem a bit intimidating. But when you're in the middle of it, it feels like you've been on tour as Beyoncé's back-up dancer for years, even if it's the first time you've set foot in a dance studio. Such is the vibe at Hipline, which was started by sisters Gabriela and Samar Nassar as a way to encourage women of all ages to enjoy the hell out of exercising. Every instructor seems like she genuinely wants to be there, and the routines — including belly dance and Hipline's own brand of dance cardio, "Shimmy Pop" — are designed so that participants can add their own moves without fumbling over complicated steps. And at the end of an hour, you'll feel like you've run a marathon — with ten-pound weights strapped to every limb. And yeah, you'll feel like you run the world.