The kettlebell or girya (Russian: гиря) is a traitional Russian castiron weight looking somewhat like a cannonball with a handle. The kettlebell has become a popular exercise tool in the United States due largely to the efforts of strength and flexibility coach Pavel Tsatsouline and also by World Champion and world record holder Valery Fedorenko. Many companies produce their own brands of kettlebells and kettlebell exercise programs. Some modern kettlebells feature adjustable weights. Kettlebell workouts are intended to increase strength, endurance, agility and balance, challenging both the muscular and cardiovascular system with dynamic, total-body movements.