As twilight approaches, Mary Beth Nishime can hardly sit still. Her inner party animal is purring, and its insatiable hunger can only be quelled with a hearty helping of beats, moves, and action. Fortunately, Zumba provides all three, plus the joyful atmosphere common to Latin salsa and merengue. So Mary Beth and her crew move the party to local churches, schools, and senior centers, where students of all fitness levels melt calories and stress with each chest pop and hip swivel. A team of teachers leads many of the church-based classes, filling the room with more energy than a newborn quasar. And to help students vary workouts, Mary Beth also hosts boot camps, yoga classes, and kickboxing sessions at her dojo, Nishime Family Karate.