Kettlebell Skull Crusher

What the kettlebell skull crusher actually trains

A kettlebell skull crusher is a triceps isolation exercise performed lying on a bench with a kettlebell in each hand and the upper arms roughly vertical, bending the elbows to lower the bells past the head and extending back to lockout.

All three heads of the triceps brachii produce the elbow extension. Kholinne and colleagues examined the role of each head and found the medial head active throughout the movement, with the lateral head recruited more heavily as demand increases and the long head's contribution dependent on where the shoulder sits. The anconeus assists near lockout, and the forearm flexors work hard simply to keep an offset weight where you put it.

The shoulder position is what makes this better than a pushdown. Lying down with the upper arms pointing at the ceiling puts the shoulder at roughly ninety degrees of flexion, which means the long head, the only head that crosses the shoulder, starts each rep partially lengthened. Tilt the upper arms slightly back towards your head and it lengthens further.

Maeo and colleagues found elbow extension trained with the arm overhead produced substantially greater triceps growth, particularly of the long head, than the same training with the arm at the side. A skull crusher sits between the two. It is not a full overhead position, but it is considerably closer to one than any pushdown, and that is the honest reason to include it.

The kettlebell part changes less than you might hope. The handle sits above the mass, so the bell hangs behind your wrist rather than balancing over it. That makes the load want to rotate, which recruits your grip and forearms more and forces you to be tidier. It does not make the triceps work differently. If you find kettlebells awkward here, a dumbbell or an EZ bar does the same job with less fuss.

Setting up and executing

Sit on a flat bench with a kettlebell in each hand, lie back, and bring the bells to your chest.

Press them up so the upper arms point at the ceiling, then rotate the wrists so the bells hang behind your hands rather than sitting on top of them.

Tilt the upper arms slightly back towards your head. This small adjustment is what lengthens the long head, and it is the difference between a good skull crusher and a mediocre one.

Bend the elbows and lower the bells past the sides of your head until you feel a strong stretch through the back of the arm.

Extend the elbows back to lockout without letting the upper arms travel, pause briefly, and repeat.

The mistakes that cost you the most

Turning it into a press is the fault that quietly ruins the exercise. As fatigue arrives, the upper arms start swinging back on the way down and forward on the way up, which shares the load with the chest and shoulders. If the upper arms are moving, the weight is too heavy.

Lowering to the forehead is a habit inherited from the exercise's name. Stopping at your face leaves range on the table. Pedrosa and colleagues found training at long muscle lengths produced favourable hypertrophy outcomes, and here the long position is behind your head, not above your nose. Let the bells pass beside your ears.

Letting the bell roll on the wrist is the specific kettlebell problem. Because the mass hangs off centre, a loose grip lets it rotate mid rep, which is uncomfortable and occasionally alarming. Grip hard and keep the wrist neutral.

Going too heavy hurts here more than on most isolation work. The elbows are the limiting joint, and an offset load in a stretched position at heavy weight is exactly the combination that leaves them sore.

Ignoring the shoulder position gives away the main advantage. Upper arms straight up is fine; upper arms tilted back is better.

Sets, reps and rest by goal

Moderate reps, controlled tempo, sensible loads.

For muscle gain, three sets of ten to fifteen with ninety seconds rest. For strength, three sets of eight to ten with two minutes, though heavy skull crushers are a poor bargain for the elbows. In a fat loss phase, three sets of twelve to twenty with a minute.

Control the descent over two to three seconds. Schoenfeld and colleagues compared concentric and eccentric actions and found broadly similar hypertrophy when volume is equated, so the case for a slow negative here is not that eccentrics are special; it is that a stretched elbow position under an offset load is not somewhere to be careless.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy. Triceps already receive substantial volume from your pressing, so six to ten hard direct sets a week is a reasonable target rather than a floor to be exceeded.

Refalo and colleagues found stopping a rep or two short of failure produces comparable growth to going all the way, which suits this exercise particularly well.

Where it fits in your split

Late in a push or arm session, after the pressing.

On push, pull and legs it comes after the bench and overhead work. On an upper and lower split it goes at the end of the upper session. On a bro split it works as the main triceps movement on arm day. On a full body programme it is optional and only worth the slot if arm size is a priority you have actually named.

Its value in a programme is positional. If your other direct triceps work is pushdowns, this covers a shoulder angle those never reach. If your other work is overhead extensions, this adds relatively little and you would be better off adding sets to what you already do.

Twice a week is comfortable, or once if your pressing volume is already high.

Variations worth knowing

The EZ bar skull crusher is the classic version, easier to load in small increments and considerably kinder to the wrists than a straight bar or an offset bell.

The dumbbell skull crusher is the closest relative, with a balanced load and the same arm position, and for most people it is the more sensible default.

The incline skull crusher, performed lying on an incline bench, tilts the upper arms further back and lengthens the long head more.

The overhead kettlebell extension, seated or standing with the arms fully overhead, is the position Maeo and colleagues' work points towards and the best single choice for long head growth.

The cable overhead extension delivers the same shoulder position with constant tension through the whole range and no balance problem at all.

And the close-grip bench press is the compound alternative, allowing far heavier loading of the triceps at the cost of specificity.

What the evidence says

Maeo and colleagues found that elbow extension trained in an overhead arm position produced substantially greater triceps hypertrophy, particularly of the long head, than the same training performed with the arm at the side. A lying extension is partway to that position, which is the main argument for choosing it over a pushdown.

Kholinne and colleagues examined the different roles of the three triceps heads during elbow extension and found the medial head active throughout with the lateral head recruited more as demand rises, which is a reminder that every head works on every rep and only the emphasis shifts.

Pedrosa and colleagues found training at long muscle lengths produced favourable hypertrophy outcomes compared with short length training, supporting the descent past the head rather than to the forehead.

Pallarés and colleagues found full range training beat partial range training for strength and hypertrophy, which is the same message from a different angle and applies to the lockout as well as the stretch.

Schoenfeld and colleagues compared concentric and eccentric muscle actions and found broadly similar hypertrophy when volume is equated, which tempers the claim that slow negatives are the key variable while leaving control as a sensible practice.

Schoenfeld and colleagues found a dose response between weekly hard sets and muscle growth, which for triceps must be counted alongside all your pressing volume.

Refalo and colleagues found stopping short of failure produces comparable hypertrophy, which is convenient on an exercise where the failed rep involves a weight above your face.

Common questions

Why use kettlebells instead of dumbbells?

Mostly because they are what is available. The offset handle makes the load want to rotate, which asks more of your grip and forearms and forces cleaner technique. For the triceps themselves it changes very little, and a dumbbell or EZ bar is easier to load and to progress.

Where should the bells go at the bottom?

Past the sides of your head, not to your forehead. The stretch is the productive part of this exercise, and stopping at the face gives it up.

Is this better than a pushdown?

For the long head, yes, because the shoulder is flexed and the muscle starts each rep lengthened. For convenience and safety, a pushdown wins. If you can only do one, an overhead extension beats both.

How is it different from an overhead extension?

Only in shoulder angle. Lying down puts the shoulder at about ninety degrees of flexion; overhead work takes it further. Maeo and colleagues found the fuller overhead position produced the greater long head growth, so treat this as a good option rather than the best one.

My elbows ache the day after. What do I change?

Reduce the load, slow the descent, and stop just short of a hard lockout at the top. If it persists, switch to a cable overhead extension, which loads the same range without the joint stress that a free weight in a stretched position creates.