Kettlebell: From Wikipedia
The kettlebell or girya (Russian: ги́ря) is a cast-iron weight (resembling a cannonball with a handle) used to perform ballistic exercises that combine cardiovascular, strength and flexibility training. Russian kettlebells are traditionally measured in weight by pood, which (rounded to metric units) is defined as 16 kilograms (35 lb).
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 or steel shot, water, or which take a variable number of plates. They also have a center of mass extended beyond the hand and allow for swing movements and release moves with added safety and added grip, wrist, arm and core strengthening due to the shifting fill material.
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”.