Muscle guide · Chest and shoulders
Also called delts, shoulder muscle
The deltoid is the triangular muscle that forms the rounded cap of the shoulder, named after the Greek letter delta. It has three parts that start on the collarbone, the tip of the shoulder and the ridge of the shoulder blade, and meet on a bump halfway down the outside of the upper arm.
Together they lift the arm out to the side; separately, the front part swings the arm forward and the rear part swings it back, as your arms do when you walk.
Source 1
| Part | Starts at | Attaches to | What it does |
|---|---|---|---|
| Front (anterior) | Outer third of the collarbone | Bump on the outside of the upper arm bone (deltoid tuberosity) | Lifts the arm forward and turns it inward |
| Side (lateral) | Top of the shoulder tip (acromion) | Deltoid tuberosity | Lifts the arm out to the side, from about 15 to 100 degrees |
| Rear (posterior) | Ridge across the back of the shoulder blade | Deltoid tuberosity | Takes the arm back and turns it outward |
Source 1
Because it pulls almost along the arm bone, the deltoid cannot lift the arm from the side on its own; the rotator cuff, especially the supraspinatus, helps start the movement and keeps the joint centred. Sources differ on whether that handover is at about 15 degrees or the two simply work together throughout.
Front raises worked mainly the front deltoid; lateral raises with a straight arm and the arm not turned out worked the side deltoid most; reverse flys and prone raises with the thumb out reached 87 to 88% of maximum in the side and rear deltoid.
3D demoStanding overhead pressIntermediate · A barbell + A dumbbell
3D demoDumbbell lateral raiseBeginner · A dumbbell
3D demoFront raiseBeginner · A dumbbell
3D demoBent-over reverse flyIntermediate · A dumbbell
3D demoFace pullIntermediate · A band
3D demoScaption raiseBeginner · A dumbbell
3D demoArnold Dumbbell PressIntermediate · A dumbbell + A bench or boxIn people with tight shoulders, the cross-body stretch improved inward rotation by 20 degrees over 4 weeks.
Damage to its nerve, from a shoulder dislocation, surgery or crutch overuse, weakens or paralyses the deltoid. Being unable to lift the arm is not always the deltoid itself: rotator cuff tears and conditions like polymyalgia can cause it too.
Source 1
In overhead athletes such as pitchers, swimmers and volleyball players, the axillary nerve and an artery can be squeezed in a gap at the back of the shoulder.
Source 7
Each grade rates the evidence for the correction.
Turning the arm outward shifted lateral-raise work toward the front deltoid. A straight arm in neutral or turned slightly in worked the side deltoid most, though turning it in also adds upper trapezius.
Source 2
A shoulder workout for all three heads: overhead press, lateral raises, reverse flyes, face pulls and rotations.
40 minIntermediate8 movesA band, A barbellA push day workout for chest, shoulders and triceps: bench press, overhead press, incline dumbbell press, lateral raises and pushdowns.
55 minIntermediate10 movesA band, A barbellA gym upper body workout for chest, back, shoulders and arms: bench press, rows, presses, pulldowns, raises, curls and pushdowns.
50 minIntermediate13 movesA band, A barbellThe front (anterior) part on the collarbone, the side (lateral) part on the tip of the shoulder, and the rear (posterior) part on the shoulder blade.
Reverse flys and prone raises with the thumb turned out reached 87 to 88% of maximum activity in the rear deltoid.
Lateral raises with a straight arm, not turned outward. Turning the arm out shifts work to the front deltoid.
It works the front deltoid, and more so the steeper the incline; front deltoid activity was highest at 60 degrees in one study.
Anatomy and movement education, not a diagnosis or treatment plan. If you have pain that follows an injury, is severe or getting worse, or comes with numbness, weakness or swelling, get it assessed. Health disclaimer.
