t's funny how workout trends come and go, and how a centuries-old piece of cast iron can inspire legions of exercisers in 2010. That's the way it seems to be going for the good ol' kettlebell. These cannonball-shaped iron orbs with handles lifted in a swinging motion were developed by Russian strongmen in the early 1700s as a way to build strength, balance, flexibility and endurance quickly.
And they do work well. If you want proof (at least anecdotal), rent the film epic 300 and take a look at the physique of lead actor Gerard Butler who plays King Leonidas of Sparta. Butler used kettlebells to prepare for his role in the film. But it's not just Hollywood types who are getting into it. Kettlebell-themed fitness classes are now being offered at gyms across the country. “It's great because it brings cardio and strength training together in one quick exercise,” says Michael Shade, kettlebell instructor at Sports Club/LA in Miami. “Instead of lifting weights for a half hour and doing the treadmill for another half hour, you can get everything done with kettlebells in 20 minutes.” Shade says that in his gym, kettlebells went from gathering dust in the corner to becoming so popular there is now a waiting list for his weekly kettlebell bootcamp classes. There are even kettlebell-only gyms opening around the country that attract exercisers who really like the simple, total-body exercises. Given kettlebells' surge in popularity, the American Council on Exercise (ACE) decided to look into the science behind this workout trend. The Study To analyze the energy cost and exercise intensity of kettlebell workouts, ACE enlisted the help of the research experts at the University of Wisconsin, La Crosse Exercise and Health Program. The team, led by John Porcari, Ph.D., and Chad Schnettler, MS, recruited 10 volunteers, male and female, ages 29 to 46 years, all of whom were experienced in kettlebell training. “They [kettlebell enthusiasts] make these all-encompassing claims about increasing your muscular strength, endurance and aerobic capacity with kettlebells, like, if you do this, that's all you need to do,” says Porcari. “So we wanted to look and see how much of an aerobic workout you really do get and how many calories you really burn.” Prior to beginning the actual study, each volunteer was given a maximal exercise test on a treadmill while oxygen consumption and heart rate were constantly monitored. Next, they surveyed each subject and their ratings of perceived exertion (RPE) for the treadmill test. Once a fitness baseline was established, each subject returned to the Human Performance Laboratory on a separate day to perform a five-minute kettlebell V• O2 max snatch test to establish a baseline of their specific kettle