Founded by dancer Judi Sheppard Missett in 1969, Jazzercise and the network that it formed has mushroomed into more than 7,800 instructors teaching 32,000 weekly classes in 32 countries. Much like the opening arguments in any trial, every 60-minute session begins with a gentle warm-up to limber up limbs before jumping into an easy-to-follow aerobic-dance routine. Moves blend elements of jazz dance with kickboxing and the core toning elements of Pilates and yoga. Top 40 hits, jazz, country, funk, rock, blues and hip-hop pluck at brain strings to get bodies energized as sessions transition into a muscle-toning segment performed with dumbbells. Workouts conclude with a stretch and cooldown.