Triceps extension
Also called skull crusher, lying triceps extension, overhead triceps extension, French press.
What is a triceps extension?
A triceps extension is any exercise where the upper arm is held still and the elbow straightens against resistance: lying on a bench with the bar coming down past your forehead, which people call a skull crusher, or with the arms overhead and the weight lowered behind your head. It trains the triceps brachii — all three heads, which share one tendon and all extend the elbow — helped by the anconeus, a small muscle just past the elbow. Only the long head also crosses the shoulder, so where you put your arm changes how long that head is at the start of a rep; which position you use comes down to preference.
How do you perform a triceps extension?
Set up
- Lie on a bench with your feet flat, hold an EZ-bar or barbell a little inside shoulder width and press it to straight arms.
- Set your ribs down and angle your upper arms slightly toward your head so the bar is over your forehead.
Execution
- Bend your elbows and lower the bar behind your head under control, keeping your upper arms still.
- Stop when your forearms meet your upper arms or your shoulders limit the range.
- Straighten your arms without letting your elbows widen.
Common mistakes
Letting the upper arms swing as you press, so the shoulder helps
Once the shoulder joins in, the muscles that pull the upper arm down finish the rep and the triceps stops being what completes it. The tell is a bar that keeps moving while the elbow angle barely changes. You have swapped exercises without noticing, usually in the last three reps, which are the ones you were doing the set for.
Flaring the elbows wider as the set gets hard
Widening the elbows turns the last reps into a close-grip press, which is a stronger position and a different exercise. The reps still get completed, so it feels like a good set — but the triceps did less of it than the rep count suggests, and the next session's weight is chosen from a lie.
Lying down and lowering the bar to your forehead with the upper arms straight up
With the upper arm vertical the weight sits directly over the elbow at the top of the rep, so there is almost nothing for the triceps to resist there — you rest at lockout and work only the bottom half. Angling the upper arms back far enough that the bar finishes over your forehead is what loads the whole rep, and it is also what stops the bar arriving at your face.
Loading it like a press
This is one joint moving through a short range, and the weight that lets you keep the upper arm still is the weight that trains it. Past that point the extra load is carried by the shoulder drifting, which is the first mistake in this list wearing a heavier plate.
Training through pain at the back of the elbow
Chronic pain at the point of the elbow that worsens when you actively extend it is the described presentation of triceps tendinitis, an overload problem. Reaching for the same bar next week is how a session's annoyance becomes a month off pressing. Change the implement or the arm position, drop the load, and if it keeps happening ask someone qualified rather than the internet.
Where it fits in a session
Late in an upper-body or push session, after the pressing, alongside a pushdown rather than instead of one.
Single joint, short range, small muscle: this does not need to be heavy to do its job, and heavy is exactly where the upper arm starts moving. Sets taken close to failure with a still upper arm beat a lower-rep set you have to heave. If you already do pushdowns, the case for keeping both is that the arm is in a different place, not that one is better — and it is what lifters already do, since a pushdown shows up in about a fifth of the sessions that contain an extension.
Muscles worked
- triceps brachii (long head)
- triceps brachii (lateral head)
- triceps brachii (medial head)
- anconeus
The three heads are listed as co-actors rather than ranked. Anatomy gives all three the same job — every head inserts on the olecranon through one shared tendon and every head extends the forearm at the elbow — so nothing in the anatomy ranks them for one version of this movement over another. One asymmetry is real and is worth knowing: only the long head crosses the shoulder, originating on the scapula rather than the humerus, so arm position changes its length while the medial and lateral heads are unaffected by where the shoulder is. That is an anatomical fact and not a training result; this page makes no claim about which arm position grows which head. Anconeus is secondary because it is a small muscle with the same action, not because its share was measured.
What lifters actually do
Just over half of regular RepCount users have logged a triceps extension at some point, and it appears in about one workout in sixteen. Four of the five exercises it shares a session with most often are pressing or shoulder work: the bench press and lateral raises in roughly a third of those sessions each, then incline dumbbell press and dumbbell shoulder press. The fifth is a pushdown, which turns up in about a fifth of the workouts that contain an extension — so this is push-day arm work, and lifters do not treat it as the one triceps slot in a session. A session that contains an extension holds around seven exercises, about three sets of which are the extension itself.
Most often trained alongside
Share of triceps extension sessions that also include each exercise.
- Bench press31.5%
- Lateral raises31.2%
- Incline dumbbell press24.4%
- Dumbbell shoulder press22.8%
- Pushdowns20.8%
Figures come from workouts tracked in RepCount.
Variations
- Lying barbell triceps extension (skull crusher) — The default form of the movement: on a bench, bar coming to or past the forehead.
- Lying EZ-bar triceps extension — Same movement on an angled bar, which lets the wrists sit at a less extreme angle.
- Lying dumbbell triceps extension — Palms facing each other, so each arm chooses its own path instead of being tied to a bar.
- Overhead dumbbell triceps extension — One dumbbell in both hands, arms beside the ears. Shoulder is flexed, so the long head starts longer.
- Single-arm overhead triceps extension — One arm at a time, seated or standing. The free hand can support the working elbow.
- Overhead cable triceps extension — Rope on a low or high pulley, facing away. Load stays on the muscle where a free weight goes light.
- Incline triceps extension — Lying on an incline bench, which tilts the upper arm back so the triceps still has something to resist at lockout.
Frequently asked questions
What muscles do triceps extensions work?
The triceps brachii, with the anconeus helping. The triceps has three heads — long, lateral and medial — and all three converge into a single tendon that attaches at the point of the elbow, so all three extend the elbow on every rep. The anconeus is a small muscle sitting just past the elbow on the outside of the forearm; extending the elbow is its job too. Nothing in the anatomy ranks the three heads for one version of this movement over another, so this page does not rank them.
Are overhead or lying triceps extensions better?
This page does not claim either one is better: settling that would take a reading of the training literature, and this page has not done one. What is settled is narrower. The long head is the only one of the three that runs past the shoulder and attaches to the shoulder blade, so raising the arm overhead lengthens it, while the medial and lateral heads originate on the upper arm bone and do not care where your shoulder is. That is anatomy, not a training result — how much it matters for growth is the separate question this page has not reviewed. Choose the position your shoulders and elbows tolerate and that you can add weight to over time.
Is a skull crusher the same thing as a triceps extension?
A skull crusher is one kind of triceps extension: the lying version, done on a bench with the weight coming down toward or past your forehead. Overhead extensions are the same movement with the arm somewhere else. The defining feature is that the upper arm is held still and the elbow does the work — the name only tells you where your arm is while that happens.
What is the difference between a triceps extension and a pushdown?
Where your upper arm is. In a pushdown it hangs at your side with the resistance coming from above; in a lying or overhead extension the arm is out in front of you or behind your head. The elbow joint does the same thing in both. The one anatomical difference worth knowing is that the long head of the triceps also crosses the shoulder, so the two put it at different lengths. Lifters often run both in the same workout rather than treating them as substitutes: in RepCount's tracked workouts, a pushdown appears in about a fifth of the sessions that contain a triceps extension.
Does the triceps extension work the long head?
Yes. All three heads pull on the same tendon at the elbow, and the anatomy gives all three the same action. The question people usually mean is whether it works the long head more than some other triceps exercise does, and that is an emphasis claim this page has not tested and does not make. What the anatomy does establish is that the long head is the only one attaching above the shoulder joint, so it is the only one whose starting length changes when you take the arm overhead.
Why do my elbows hurt when I do skull crushers?
This page will not diagnose you, and the honest answer is that elbow pain has several causes. What the anatomy reference describes is that chronic pain at the back of the elbow which worsens when you actively extend the arm is the typical presentation of triceps tendinitis, a tendon overload problem. Pain that shows up in the same spot every time you do one movement is information rather than something to train through. Changing the implement, the arm position or the load is the usual first move, and a professional opinion beats a heavier set.
Are triceps extensions worth doing?
In RepCount's tracked workouts, just over half of regular users have logged one, and they show up in roughly one workout in sixteen. Four of the five exercises they most often share a session with are pressing or shoulder work: the bench press and lateral raises in about a third of those sessions each, then incline dumbbell press and dumbbell shoulder press. That is the profile of a standard push-day accessory — widely used, rarely the point of the session.
Sources
- Tiwana MS, Sinkler MA, Bordoni B. Anatomy, Shoulder and Upper Limb, Triceps Muscle. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK536996/
- Glover NM, Black AC, Murphy PB. Anatomy, Shoulder and Upper Limb, Radial Nerve. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK534840/
- Mitchell B, Whited L. Anatomy, Shoulder and Upper Limb, Forearm Muscles. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK536975/