Unlike traditional gyms that take a laissez-faire approach to fitness, letting clients fumble through their own workouts, Orangetheory leads exercisers in innovative personal group-training sessions that run through four distinct steps. Inside the warm, citrus glow of each facility, dozens of treadmills, rowing machines, free-weight sets, and Trx suspension systems await the next interval changeover. Music sends electric currents of energy through the atmosphere as patrons sweat out calories, and personal trainers patrol the aisles, giving pointers for touching up form and blinking out motivational words in Morse code. Clients keep an eye on their heart-rate readouts to ensure they're in the peak range for burning fat and building muscle. After an hour—during which guests complete a 10- to 30-minute interval at each of the four stations—the "orange effect" sets in and jump-starts metabolisms, possibly for days after the workout has ended.

Orangetheory Fitness has been highlighted in the New York Times for its seminal workout plan, which was designed by Florida fitness expert Ellen Latham to help people to turn their workout plateaus into springboards. With more than 50 classes per week at each location, members can capitalize on the gym's personal-training vibe and stimulating group setting at their leisure.