The growing popularity of kettle bells, the primitive-looking bowling-balls-with-handles that deliver a great all-body workout, has given rise to similar products with more flexibility. Available now are weight-changeable kettle bells that can be customized to new fitness levels, for different family members or even during a workout — so you don't have to own more than one. Below, find four innovative ways to throw your weight around. — Roy M. Wallack
Likes: It works perfectly. The design is handsome and efficient; just slide a spring-loaded handle on the top and release the desired number of plates. It's safe because the handle can't be moved unintentionally. Two models are available: the 40-pound max, with a 10-pound handle/frame and a half-dozen 5-pound weights, and the 20-pound max, with a 5-pound handle and 21/2-pound plates. Both come with a workout DVD and a healthful-eating guide.
Dislikes: It works fine for standard swings and dead lifts, but overhead presses are a no-go; the cylindrical (not spherical) shape, horizontal plate stacking and sharp plastic top edge uncomfortably scrapes your forearm when flipping it over to the back of your hand. It rattles a bit, and the 1-inch-wide handle is thinner and less comfortable than that of a normal kettle bell.
Price: $249.99 (40-pound); $99 (20-pound). (888) 308-9617; http://www.weiderfitness.com.
U-Fill-It Kettlebell: Hollow 2-pound plastic kettle that can be filled with water (12 pounds), sand (18 pounds) or metal shot (49 pounds).
Likes: Very user friendly. The smooth, hard, rounded plastic and thick handle feel great in your hands. It glides smoothly across your skin at all times. It fills easily through a 21/2-inch-wide port on the bottom; the threaded plug is locked tight with a dedicated four-pronged wrench. Quite durable and leak-free when tightened properly, and it did not crack after dropping it during juggling and hand-to-hand drills.
Dislikes: Switching between weights during the workout, as done easily with the Weider, would be a messy hassle, requiring dumping the water and pouring in a bag of sand or shot. Beware misplacing the wrench, because hand-tightening the plug could be leaky.
Price: $49. (866) 89-Punch; http://www.theartofstrength.com.
BYOP (Bring your own plates)
Kettlestack: Handled device with minimalist frame that allows you to bolt on your own weight plates. Includes a standard Allen wrench, a center axle to hold the weights and a variety of male/female bolts.
Likes: It works just like a regular kettle bell, which can grow with your fitness as you add weight plates. I cannibalized some old dumbbells and built a 321/2-pound kettle bell out of four 5-pound plates and five 21/2-pounders. It looked ugly and primitive, but my rounded plates didn't feel uncomfortable on presses, like the Weider. Weights above 85 pounds will require wider axles ($12).
Dislikes: Sharp-edged plates would not feel good against your skin. Changing weights during a workout is slow compared with the Weider, but simple and fast enough to adjust for another user.
Price: $55. (866) 423-0922; http://www.kettlestack.com.
Sandbells: Not a kettle bell but a soft, handleless, nylon-coated neoprene sack filled with sand or shot that you grab at the edges and use for kettle bell movements — and more.
Likes: Strenuously works your hands and fingertips. The precarious grip and shifting sand add a new level of difficulty to "easy" movements, such as swings. It encourages the creation of challenging exercises, such as swinging overhead, 10-foot throws or downward ground slams. I did 20 throws with the 30-pounder and was gasping for breath. House-friendly, the tough but soft, bag won't rip and will not dent hardwood floors. Available in weights from 2 to 50 pounds. It's adjustable — you can pour sand in or out, altering weight and grip. (Optional funnel is $2.) It can be emptied for travel.
Dislikes: Might be too much work for some. The hand fatigue shortens the exercise duration. No DVD is included, although several Sandbell workouts are found on YouTube.
Price: 10-pounder (empty $16.99; filled $18.69); 20-pounder ($39.99, $43.99); 30-pounder ($59.99; $65.99). (888) 460-0628; http://www.hyperwear.com.
Wallack is the author of "Run for Life: The Breakthrough Plan for Fast Times, Fewer Injuries, and Spectacular Lifelong Fitness." email@example.com.