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. It is also the main equipment used in the weight lifting sport of girevoy sport. Russian kettlebells are traditionally measured in weight by pood, which (rounded to metric units) is defined as 16 kilograms (35 lb). Even in American gyms kettlebells will often be referred to in the weight system of poods.
Kettlebell Swing: The kettlebell swing ( Instructional Video ) is a basic kettlebell exercise that is used in training programs and gyms for improving the posterior chain muscles. Kettlebell swings are an easy exercise to intensify by using a heavier kettlebell, increasing the repetitions and/or sets, or by doing one-armed kettlebell swings.
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.
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".
The movements used in kettlebell exercise can be dangerous to those who have back or shoulder problems, or a weak core.[dead link] However, if done properly they can also be very beneficial to health. They offer improved mobility, range of motion and increased strength. 
Kettlebells were developed in Russia in the 1700s. The Soviet army used them as part of their physical training and conditioning programs in the 20th century. They had been used for competition and sports throughout Russia and Europe since the 1940s. Though kettlebells had been in the United States in some form since the 1960s or earlier, Dragon Door Publications and Pavel Tsatsouline developed the first instructor certification program in the USA in 2001.
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