Weightlifting involves the lifting of weights attached to a barbell. People lift weights for exercise and to build their muscles. Weightlifting also serves as the basis of competitive sports called weightlifting and powerlifting. In these sports, athletes compete to determine who can lift the most weight. Such competitions match lifters with similar body weights. Athletes who participate in other sports sometimes lift weights to increase their strength and flexibility. Lifting weights is also a popular hobby for improving muscle tone and general health. Professional bodybuilders lift weights to improve their muscular development. They exhibit their physiques in organized competitions. Judges decide which bodybuilder has the best body.