Deltoids

The deltoids wrap around the top of the shoulder from front to back & span the clavicle, the acromion, & lateral half of the scapula. This muscle group is divided into the anterior, middle, & posterior deltoids. Similarly to the gluteal muscles in the hip, the point of their attachment largely determines their function. The anterior deltoids assist with flexion & external rotation of the shoulder. The middle portion abducts, & the posterior deltoids assist with extension & external rotation.