Skull crushers: technique and how to protect your elbows

Does the back of your elbow ache for a day or two after arm training, right on the bone? The skull crusher is usually the first suspect. It gives you as much triceps sensation as anything in the gym, and it punishes sloppy reps faster than almost any other arm isolation.

That does not make it a bad exercise. Most elbow grumbling comes down to four things: too much weight, a rushed lowering phase, elbows drifting wide, and a hard snap into lockout. All four are fixable without giving up what the movement is good at.

What the exercise is and which muscles it works

The skull crusher, also called the lying triceps extension or French press, is a triceps isolation. You lie on a bench, keep the upper arms roughly still, and the movement happens at the elbow only: the bar travels towards your forehead or past the top of your head, then back up.

The triceps has three heads. The long head attaches to the shoulder blade and is the only one that crosses the shoulder joint, so it gets stretched when the arms go overhead or slightly behind the line of the shoulders. The lateral and medial heads only straighten the elbow, and they do most of their work near the top of the rep.

Angle the upper arms back a little and the long head works in a longer, stretched position. The evidence is currently strongest for muscles responding well to serious loading in exactly that stretched range, which is why this movement earns its place. The forearm and hand work too, simply keeping the bar steady.

How to do it

1. Pick up an EZ bar. The semi-pronated grip is usually kinder to wrists and elbows than a straight bar. Grip at shoulder width or slightly narrower.
2. Lie on a flat bench, feet planted, shoulder blades lightly set, natural arch in the lower back.
3. Press the bar out to a start position above the chest with the arms straight.
4. Tilt the upper arms 10 to 20 degrees towards your head so the elbows sit slightly behind the shoulder line. This keeps tension on the triceps at the top instead of dumping it onto the joint.
5. Keep the elbows parallel and no wider than your shoulders for the whole set.
6. Lower under control for two to three seconds, past the forehead, until the bar finishes behind the top of your head and the forearms are at or just below parallel with the floor.
7. Stop where you feel a full stretch in the triceps. No bouncing, and no dropping through the last few centimetres.
8. Come back up by straightening the elbow. The upper arm stays put; do not let the shoulders join in and drag the bar towards your feet.
9. Stop just short of a locked elbow, squeeze the triceps, then go again.
10. Breathe in before you lower, out towards the end of the way up. Do not hold your breath for the whole set.

The usual mistakes

Too much weight. This causes most of the others. When the load is heavy, the upper arms drift back and the lift turns into a half pullover, with the tension leaking onto the lats and shoulders. If you have to heave the first two reps, take 15 to 20 per cent off.

Elbows flaring out. Flaring hands part of the job to the chest and shoulder and puts the elbow on an awkward line. Picture the upper arms strapped together.

Dropping the bar. The triceps tendon attaches to the point of the elbow and does not enjoy sudden yanks at the end of the stretch. A slower eccentric is often the whole difference between a set that builds and a set that aches for three days.

Slamming into lockout. Snapping the arm straight adds almost nothing for the muscle and adds an impact to the joint on every single rep. Stop a fraction short.

Broken wrists. If the bar slides into the fingers, the wrist bends back and you feel the pull on the inner elbow. Keep the bar stacked over the heel of the hand, wrist in line with the forearm.

Going in cold. Skull crushers as the first movement of the session, with no build-up, is a needless risk. Do two or three ramp-up sets, or put them after your pressing.

Half reps. Cutting the range short gives you less stimulus and saves the elbow nothing, because the load stays heavier than it needs to be.

Easier variations

Dumbbells, neutral grip. Palms facing each other, each arm free to find its own line. For most people this is the first swap to try when the bar bothers them.

Cable and rope. Lie on a bench in front of a low or mid pulley. The resistance is more even through the range and the hardest point is not exactly where you are most stretched, which usually feels better at the elbow.

Shorter range. If the last stretch of the movement is the problem, work in the pain-free portion for a few weeks and add depth back gradually.

Lighter and longer. Sets of 15 to 20 with clean form do the job while cutting the peak load on the tendon.

Harder variations

Slower eccentric. Four to five seconds down with the same weight is effectively a different exercise.

Paused reps. One second still in the stretched position removes every bit of bounce and shows you exactly what you can handle.

Deeper behind the head. Set up so the bar can travel below bench level and the long head gets a longer stretch. Light loads and full control only.

Single-arm dumbbell version. Exposes side-to-side differences and demands more stability.

JM press. A hybrid of the skull crusher and a narrow press. It tolerates heavier loading, but only once your technique is solid.

Alternatives if you have no equipment

The triceps does not need much. Close-grip and diamond press-ups cover similar ground, and you can raise your feet to make them harder. If you want the loaded version of the same pattern, the close-grip bench press is the closest fit and takes real weight.

A bodyweight triceps extension on a low bar or rings, where the body leans forward and only the elbow moves, is nearly the same movement. A band anchored behind you allows overhead extensions, and a single dumbbell held in both hands overhead gives you a seated French press.

Bench dips do hit the triceps, but they park the shoulder in an awkward position, so skip them if the front of your shoulder complains.

How many sets and reps

For most people: 2 to 4 sets of 8 to 15 reps, once or twice a week. If your elbows are sensitive, live at the top of that range, 12 to 20 reps with a lighter bar.

Six to twelve weekly sets is plenty for the triceps in total, counting what it already gets from pressing. If you bench three times a week, two or three direct sets per session is enough.

Leave one to three reps in reserve. Training to failure here buys little, and the form falls apart on exactly the rep where the elbows start wandering. Rest 90 to 120 seconds.

Progress reps first, load second. Once you hit 3 sets of 12 cleanly two weeks running, add a kilo or two and let the reps drop back to 8 to 10.

Who it suits, and when to leave it out

It suits you if you want bigger arms and a stronger finish on the bench press. In people who press a lot, the long head tends to lag because pressing never puts it in a long position, and this is where it gets that.

Drop it, or switch to the cable version, if you have current elbow pain, if soreness lasts longer than 48 hours, or if it creeps up week after week. If a stiff shoulder stops you holding the upper arms comfortably in place, sort that first; the work that actually helps the rotator cuff is worth more than forcing range you do not have.

Older lifters have no reason to avoid the movement, but the principles behind sensible training in your fifties fit it well: longer warm-ups, smaller jumps in load, more reps. Pain during a set is not a sign the exercise is working.

When to see a doctor

See a doctor or physiotherapist if you have sharp pain with swelling around the elbow, a clear loss of strength when straightening the arm, tingling or weakness spreading into the fingers, or if you heard and felt a pop under load. The same applies if the pain has not settled after two or three weeks despite lighter loads and a shorter range. This article is not a diagnosis.

The short version

EZ bar, grip around shoulder width, elbows slightly behind the shoulder line and parallel throughout. Two to three seconds down to a full stretch, back up without slamming the lockout. Two to four sets of 8 to 15 reps, one to three reps in reserve. If the elbow protests, cut the weight and slow the lowering before you change the exercise.