Deltoid
The deltoid is the three-part muscle that wraps around the shoulder and the main force lifting the arm forwards, out to the side and backwards. It is the outer layer that makes the wide range of movement of the shoulder joint usable.
| Location | A three-part muscle wrapping the shoulder joint from the front, the side and the back |
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| Function | Lifting the arm forwards, sideways and backwards; supporting the shoulder joint during movement |
| Role in daily life | Reaching for a shelf, lifting loads, carrying a bag, and every task that uses the arm overhead |
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| Related exercises |
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| Common misconception | Shoulder width is thought to develop only through lateral raises; in fact pressing, pulling and carrying movements develop all three parts of the deltoid together, and give a more balanced result than working from a single angle. |
Three parts, three directions
The front fibres of the deltoid begin at the collarbone, the middle fibres at the point of the shoulder and the rear fibres at the shoulder blade, and all three join at the upper arm bone. The front part lifts the arm forwards and joins in with pushing; the middle part lifts it out to the side; the rear part takes it back and accompanies pulling. In almost any direction the arm moves, at least one part is on duty.
A tendency towards uneven development
In push-heavy programmes the front deltoid works a great deal and the rear deltoid very little; that imbalance can contribute to a posture with the shoulders rolled forwards. Giving pulling movements a place in the programme to balance the pushes lets the rear part take its share. For shoulder health, this balance matters more than the weight lifted.
The movements that train it
The Shoulder Press is the deltoid's main exercise; the Push-Up and the Dumbbell Bench Press work the front part, and the Dumbbell Row the rear. Carrying movements load the shoulder in its stabilising role.
Related terms: Shoulder Press, Pectoralis Major, Triceps, Latissimus Dorsi