Deltoid

The deltoid forms the rounded covering over the shoulder. It helps raise the arm, as happens during swimming. The rotator cuffs lie deeper around the shoulder joints: they are groups of muscles, rather than the visible outer shoulder covering.

The deltoid covers the top and outer part of the shoulder, giving it its rounded shape. It raises the arm sideways at the shoulder: during the outward phase of a star jump, the deltoids help lift the arms away from the body.