The pull-up is a back exercise that works the lats, teres major, rhomboids, and some forearms and biceps. Generally pulling exercises, like this one, strengthen various muscles in the back. This exercise involves holding onto a bar in a dead hang, and then pulling yourself up until your chin gets over the bar. You should not swing while doing pull-ups because that creates momentum that takes some of the work away from the muscles. It is different from the chin-up because it has a wider grip and the palms face outward. The grip position of the pull-up forces more back muscles to be used as opposed to arm muscles, like the chin-up.