Dumbbell Skull Crushers

What the dumbbell skull crusher actually trains

A dumbbell skull crusher is an elbow extension exercise performed lying on a bench, lowering a dumbbell in each hand past the sides of the head by bending the elbows, then straightening the arms again.

All three heads of the triceps extend the elbow, with the anconeus assisting at the end of the range. The long head, which crosses the shoulder as well as the elbow, is the head whose training is most affected by how you set your upper arms.

Kholinne and colleagues found the three heads contribute differently to elbow extension rather than acting as a single unit, which is why arm position is a genuine variable and not just bodybuilding lore. Because the long head runs from the scapula, its length depends on shoulder angle: arm at your side, it is short; arm overhead, it is stretched.

Tilting the upper arms back towards your head puts the shoulder into partial flexion and loads the long head at a longer length through the whole rep. Maeo and colleagues found triceps hypertrophy was substantially greater after elbow extension training performed with the arm overhead than with the arm in a neutral position, which is the strongest reason to angle the arms rather than keeping them vertical.

The dumbbell version differs from the barbell one in three small ways. The wrists can rotate to whatever angle is comfortable, which matters a great deal to lifters whose elbows dislike a fixed bar. The hands can travel past the ears independently, allowing a slightly deeper bottom position. And each arm works alone, so a stronger side cannot quietly cover for a weaker one.

What you lose is loading convenience. Getting heavy dumbbells into position over your face is awkward, and progression comes in coarse jumps.

Setting up and executing

Sit on a flat bench with a dumbbell resting on each thigh, then lie back and use your legs to help bring them to arms length above the chest.

Turn the palms to face each other and tilt the upper arms slightly back towards your head, so the dumbbells sit over your face rather than your chest.

Set the shoulders down onto the bench and brace the abs so the ribs stay flat.

Bend the elbows to lower the dumbbells past the sides of your head, keeping the upper arms fixed in place. Only the forearms should travel.

Lower until you feel a strong stretch in the back of the arm, without letting the elbows flare outwards.

Extend the elbows to full lockout, pause for a beat, and repeat without bouncing out of the bottom.

The mistakes that cost you the most

Upper arms pointing straight up is the fault that costs you most, because it quietly removes the reason to choose this exercise. With a vertical upper arm the long head is not lengthened and you are doing an ordinary elbow extension. Tilt them back.

Lowering only to the temples cuts the deepest part of the range. Dumbbells let you go past your ears, which a barbell cannot do without hitting you, and that extra range is one of the version's real advantages.

Elbows flaring outwards turns the movement into an ungainly press and loads the joint at an awkward angle. Keep them roughly shoulder width apart throughout.

Swinging the upper arms back with the dumbbells brings the latissimus dorsi in and takes the triceps out of the bottom of the rep. If the whole arm is moving, only your ego is being trained.

Going too heavy is the reliable cause of elbow pain here. The stretched position is where the joint is most exposed, and any load that forces a bounce out of the bottom is one you will regret in a few weeks.

Sets, reps and rest by goal

Programme this as your main triceps movement without treating it like a heavy compound.

For muscle gain, three sets of ten to fifteen with ninety seconds of rest. For strength, three sets of eight to twelve with two minutes. In a fat loss phase, three sets of twelve to twenty with a minute.

Stay out of very low rep ranges. Heavy sets of five in a deep stretched elbow position offer little that sets of ten do not, and cost a great deal more joint stress.

Control the lowering phase over two to three seconds. Roig and colleagues found eccentric training produced greater strength gains than concentric training, which supports resisting the descent rather than letting the dumbbells fall towards your head.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy. Aim for something in the region of eight to sixteen hard triceps sets a week in total, counting the contribution from your pressing.

Refalo and colleagues found stopping a rep or two short of failure produces comparable growth to training to failure, and here that rule has a practical edge as well: the rep you fail is the one with two dumbbells near your head.

Because each arm works alone, let the weaker side set the rep count. Liao and colleagues reviewed unilateral against bilateral training and found broadly comparable outcomes, so working one arm at a time is a convenience rather than an upgrade.

Where it fits in your split

After the pressing, on a push or arm day.

On push, pull and legs it belongs on push day once the bench and overhead work is done. On an arms day it should be the main triceps exercise. On a bro split it is the first triceps movement of the session. On an upper and lower split it follows the presses. On a full body programme it is worth a slot when arm size matters to you.

Put it before your pushdowns. Given that overhead style extension work produces more triceps growth than short arm position work, it deserves your freshest sets, and the pushdown is perfectly capable of being done tired.

A complete triceps day is this movement followed by a pushdown. Five or six hard sets, two exercises, no need for a third.

Two sessions a week is a sensible frequency. The triceps recovers quickly, but it is also getting hit by every press you do, so more than that rarely helps.

Variations worth knowing

The lying barbell triceps extension is the same exercise with a bar, which is easier to load and to progress but fixes the wrists in one position.

A single arm dumbbell skull crusher works one side at a time, which exposes side to side differences and lets the free hand support the working elbow.

An incline dumbbell skull crusher increases the shoulder angle further, adding range and stretch at the bottom.

The seated overhead dumbbell extension takes the arm fully overhead, which lengthens the long head as much as any free weight movement can.

A cable overhead extension gives you the same lengthened position with constant tension and a gentler load profile at the stretch, which suits cranky elbows.

And the rope pushdown is the short arm position counterpart, useful for accumulating volume rather than for training the stretch.

What the evidence says

Kholinne and colleagues studied the different roles of each head of the triceps brachii in elbow extension and found the heads are not interchangeable, which is the anatomical basis for caring about upper arm angle at all.

Maeo and colleagues found triceps hypertrophy was substantially greater after elbow extension training performed in the overhead position compared with the neutral arm position, which is why tilting the upper arms back matters more than any other cue in this exercise.

Pedrosa and colleagues found training at long muscle lengths produced favourable muscular adaptations, which is the broader principle behind lowering the dumbbells past your ears rather than stopping level with your head.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy, which sets the volume target once the exercise selection is right.

Refalo and colleagues found stopping short of failure produces comparable growth to training to failure, which is a useful rule on a movement where the failed rep is genuinely awkward.

Roig and colleagues found eccentric resistance training produced greater strength gains than concentric training, supporting a controlled descent into the stretched position.

Liao and colleagues reviewed unilateral against bilateral training and found broadly similar outcomes, which means working the arms separately here is about convenience and symmetry rather than superior results.

Common questions

Should the dumbbells go to my temples or past my ears?

Past your ears. That is the main advantage dumbbells have over a bar in this position, and the deeper range is where the long head is loaded at its longest. Stopping at the temples throws it away.

How is this different from a lying barbell extension?

Very little in terms of muscles trained. The dumbbell version lets the wrists rotate and allows a deeper bottom position; the barbell version is easier to load and progress. They are near duplicates, so pick one as your main lying extension rather than programming both.

Why do my elbows ache afterwards?

Almost always load rather than the exercise itself. The stretched position exposes the joint, and heavy dumbbells plus a bounce out of the bottom is the usual combination. Reduce the weight, slow the descent, and if it persists switch to a cable overhead extension.

Do I still need pushdowns if I do these?

Yes, though only one of them. This movement covers the lengthened long head position; a pushdown adds easy volume in the short arm position and is more comfortable to take to failure. Two triceps exercises is enough.

Should the palms face in or forward?

Facing each other is the default and usually the most comfortable, since it lets the dumbbells travel past your head cleanly. Turning them slightly is fine if your elbows prefer it; this is one of the few things dumbbells let you choose.