Part boot camp and part ballet class, Cardio Barre gets would-be ballerinas sweating like football players.

For those whose cocktail-filled evenings are showing up around the midsection, Cardio Barre will make a nice alternative to the local bar. Cardio Barre classes combine garden-variety aerobics with weight training and traditional ballet moves. As Britney Spears and Madonna songs thump away in the background, students complete a fast-paced routine of plies, ronde de jambes and battements combined with upper-body weight training and floor exercises. One need not have a ballet background to attend the class, but it certainly helps when doing double-time plies at the bar. (No amount of training, though, could make the seemingly endless sets of crunches any less excruciating.) Many standard moves can be quickly learned, but one class might dedicate time to calf definition, while another might focus on making your oh-so-poised triceps scream for mercy. —Elisa Jacobs