Deltoids

Deltoids: what are they?

The deltoid runs from the collarbone, the acromion and the spine of the scapula down to a single point on the outside of the humerus. Because it originates across the whole front, top and back of the shoulder and converges on one insertion, the three sections pull the arm in three different directions. That structure is why a program needs all three trained separately: no single exercise loads all of them well, and the pressing most clients already do covers only one.

Three heads, three directions

The anterior deltoid flexes the shoulder, bringing the arm forward and up, and assists in internal rotation. Every press, whether overhead or on a bench, trains it heavily. It is almost never the head that needs more volume.

The lateral deltoid abducts the arm, taking it out to the side, and it is the head that creates shoulder width. It gets some work from overhead pressing but far less than most people assume, which is why lateral raises are worth programming rather than treating as filler.

The posterior deltoid extends and horizontally abducts the arm, pulling it backwards, and it externally rotates. Rows train it when the elbows flare; they train it much less when the elbows stay close to the ribs. It is the most commonly undertrained head in clients who press more than they pull.

How to train each head

A balanced shoulder week needs a vertical press, direct lateral work, and direct rear delt work. The front head rarely needs anything beyond what pressing already provides.

Why lateral raises rarely work

Most clients do lateral raises far too heavy. The arm is a long lever and the lateral deltoid is small, so the load that actually challenges it is lower than a client's ego suggests. As soon as the weight is too heavy, the trapezius shrugs, the trunk swings, and the raise becomes a partial-range momentum exercise.

Two changes fix almost every lateral raise: reduce the weight until the movement is smooth from the bottom, and slow the lowering phase. A cable version helps too, because tension stays on the muscle at the bottom of the range where a dumbbell offers almost none.

• Start each rep from a dead stop with the arm hanging, no swing.
• Stop at roughly shoulder height; going higher shifts work to the traps.
• Lower over two to three seconds rather than dropping the arm.
• Use cables or a slight forward lean to keep tension in the stretched position.

Pressing volume and rear delt balance

A client who benches twice a week, presses overhead once and rows once has a front-to-back imbalance building. Anterior deltoid gets four exposures, posterior gets one partial one. That shows up over time as a shoulder that sits forward and gets irritated during pressing.

The correction is cheap. Two sets of rear delt work at the end of every upper-body session, plus rowing volume at least matching pressing volume, keeps the balance reasonable. Rear delts recover quickly and tolerate high frequency, so this is one of the easiest things to add to a program without disturbing anything else.