The lopsided, cannonball-shaped kettlebell works your core like crazy—sculpting, strengthening, and trimming in ways no other tool can match
To look at it, you wouldn't guess that the simple kettlebell is such a fitness hero—both a superior calorie burner and an ab flattener in one. But thanks to its unique physics, it can elicit more burn and firm than other forms of resistance.
Typical kettlebell moves are calorie guzzlers. Take the snatch (a one-arm lift in which, from a quarter-squat position, you fluidly move the kettlebell from the floor to directly overhead as you stand, bell flipping up and over to rest atop your forearm). It burns some 20 calories per minute when performed at an as-many-reps-as-possible (AMRAP) pace—the same burn rate of a super speedy six-minute mile run, according to a recent American Council on Exercise study at the University of Wisconsin–La Crosse. (Exercisers in the study did a 20-minute workout consisting of 15-second AMRAP intervals of kettlebell snatches followed by 15 seconds of rest.) "It's a total-body exercise," says lead author John Porcari, Ph.D.
By engaging the entire posterior chain (back, butt, hamstrings, and calves) plus the chest, shoulders, and arms, the kettlebell snatch and its variations work more muscle groups than other forms of HIIT, such as biking or running, which use primarily the legs and glutes. Do high-intensity kettlebell intervals like those in the study, and you'll also be dispatching more ab fat into your calorie-burning furnace than if you do steady reps of swings. (Before you try anything, make sure you're using that kettlebell properly and not making these common kettlebell mistakes you might be doing and how to fix them.)
Built-In Ab Tightening
Swinging a kettlebell calls for a braced core throughout and an added contraction of abs and glutes at the top of the swing. This pulse-like abdominal contraction stiffens your core and stabilizes the spinal column to help control the heavy, dynamic movement. It's also where women looking to cinch and strengthen their midsection can really cash in.
A recent study published in the Journal of Strength and Conditioning Research showed that when exercisers quickly squeezed their abs at the top of a swing, their obliques contracted more than 100 percent of their maximum potential. Those who didn't perform the contraction? They saw only a 20 percent side-abs engagement. "Adding a fast, explosive abdominal contraction like this allows your obliques to engage far beyond what they normally would, because every ounce of your muscles' power is needed to stop such powerful movements," Porcari says. "And when your muscles contract at a higher percentage, you'll get greater strength gains faster." (And KBs are fantastic for your booty too; try Emily Syke's Favorite Kettlebell Exercises for a Better Butt.)
Balance Challenge Benefits
Beyond the swing thing, kettlebells' bottom-heavy weight distribution offers added core-firming options. Instead of using dumbbells, Dasha L. Anderson, the founder of Kettlebell Kickboxing in New York City, ups the ante on presses and lifts by flipping the kettlebell bottom up so the bulky center teeters on a much smaller base. "Your body has to work harder—core included—to balance this and compensate for any instability," Anderson says. Her go-to ab blaster is the Turkish get-up: You fluidly raise your body from lying faceup on the floor to standing while holding a kettlebell overhead with one arm the entire time. "Throughout the Turkish get-up, it's the core that holds it all together," she says.
Even carrying one kettlebell upside down by the handle at shoulder height (arm bent down) provides this ab-flattening bonus. Stuart McGill, Ph.D., the author of Back Mechanic and multiple studies on kettlebell workouts and their effects on the spine, says that carrying weight on only one side of the body calls on the core to compensate, and the instability of the inverted bell challenges the core more than a dumbbell would. "It is a wonderful way to condition your core and also improve your motor control," McGill says.
And it does all of this without beating up on your body. "Its resistance builds muscles with enough intensity that we can really burn a lot of calories, but because we're standing in place or at least not jumping, there's no pounding on the joints," says Steve Cotter, the director of the International Kettlebell and Fitness Federation in San Diego. In other words, more ab trimming, less wear and tear. (Ready to put those muscles to work? Try this Full-Body Kettlebell Workout That Turns You Into a Total Powerhouse.)