The kettlebell is a cast-iron or steel weight (resembling a cannonball with a handle) used to perform ballistic exercises that combine cardiovascular, strength and flexibility training. They are also the primary 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 when kettlebells in Western gyms are labelled in kg, their sizes are based on units of whole and half poods (illus.).