Unlike traditional dumbbells, the kettlebell's center of mass is extended beyond the hand, similar to Indian clubs or ishi sashi. This facilitates ballistic and swinging movements. Variants of the kettlebell include bags filled with sand, water, or steel shot. The kettlebell allows for swing movements and release moves with added safety and added grip, wrist, arm and core strengthening. The unique shape of the kettlebell provides the "unstable force" for handling - key for the effectiveness of the kettlebell exercises.
By their nature, typical kettlebell exercises build strength and endurance, particularly in the lower back, legs, and shoulders, and increase grip strength. The basic movements, such as the swing, snatch, and the clean and jerk, engage the entire body at once, and in a way that mimics real world activities such as shoveling or farm work.
Unlike the exercises with dumbbells or barbells, kettlebell exercises often involve large numbers of repetitions. Kettlebell exercises are in their nature holistic; therefore they work several muscles simultaneously and may be repeated continuously for several minutes or with short breaks. This combination makes the exercise partially aerobic and more similar to high-intensity interval training rather than to traditional weight lifting. In one study, kettlebell enthusiasts performing a 20 minute snatch workout were measured to burn, on average, 13.6 calories/minute aerobically and 6.6 calories/minute anaerobically during the entire workout - "equivalent to running a 6-minute mile pace". Because of their high repetitions, kettlebell progression should start out slowly to build muscle endurance, support the joints and prevent injury.
The movements used in kettlebell exercise can be dangerous to those who have back or shoulder problems, or a weak core. However, if done properly they can also be very beneficial to health. They offer improved mobility, range of motion and increased strength.