Skull crushers have an intimidating name and an intimidating reputation for cranky elbows — but done right, they're one of the best triceps mass-builders there is, hitting the part of the muscle that pushdowns miss. Here's the honest guide. Skull crushers are a lying triceps extension where you lower a bar toward your head, and they build the triceps — especially the long head — better than pushdowns, as long as you keep your elbows in and protect the joint. Here's how to do them safely.
What skull crushers train (the honest mechanics)
Skull crushers (lying triceps extensions) are an isolation exercise for the triceps. Lying on a bench, you hold a bar (EZ-bar, barbell, or dumbbells) with arms extended, then bend at the elbows to lower it toward your forehead and extend back up. Because your upper arms are positioned back/overhead, skull crushers emphasize the triceps' long head — the largest of the three heads, which sits along the back of the arm and is best trained when the arm is overhead. This is exactly what pushdowns miss (they keep your arms down at your sides), making skull crushers a key complement for complete triceps and bigger arms.
Proper form (the movement)
Lie on a flat bench holding an EZ-bar with arms extended up, angled slightly back toward your head (not straight vertical — a slight lean keeps tension on the triceps). Then: bend at your elbows to lower the bar toward your forehead or just behind your head, keeping your upper arms fixed and elbows pointing forward. Extend back up by straightening your elbows, squeezing your triceps, without locking out hard. Keep your upper arms still — only your forearms move. The cues: upper arms fixed and angled slightly back, elbows in and forward, lower to your forehead/behind your head, control throughout. Lowering behind your head slightly increases the long-head stretch.
The elbow-flare sin (protect the joint)
The main skull crusher mistake — and the source of its elbow-pain reputation: letting your elbows flare out to the sides. When your elbows drift outward, you lose triceps tension and put awkward stress on the elbow joint. The fix: keep your elbows tucked in, pointing forward and roughly shoulder-width, throughout the movement. Combined with keeping your upper arms fixed, this keeps the work on the triceps and the joint in a safe position. Also, use moderate weight and control the descent — skull crushers punish heavy, sloppy reps with elbow strain more than most exercises. Elbows in, controlled tempo, and the "skull crusher" name stays metaphorical.
The elbow-pain reality (an honest note)
Here's an honest heads-up: skull crushers bother some people's elbows even with good form, and that's okay. The lying triceps extension position puts stress on the elbow joint that not everyone tolerates. If you feel joint pain (not muscle burn), try these fixes: use an EZ-bar (the angled grip is easier on the wrists and elbows than a straight bar), lower behind your head rather than to your forehead (often more comfortable), use dumbbells for a more natural path, or reduce the weight. If it still hurts, swap to overhead extensions or other long-head exercises — you don't need skull crushers specifically, just some overhead-position triceps work. Listen to your elbows.
Where they fit (pair accordingly)
Use skull crushers as a triceps exercise on a push or arm day, ideally paired with a pushdown — skull crushers for the long head (arms overhead), pushdowns for the lateral/medial heads (arms down) — for complete triceps. Balance your arm training with bicep work, and remember your triceps also get hit in all your pressing like the bench press. Use controlled, moderate weight. Progress with progressive overload. They build the muscle; a calorie deficit reveals it.
Quick answers
What do skull crushers work?
The triceps, with emphasis on the long head (the largest head), since your arms are positioned back/overhead.
Why are skull crushers good?
They train the long head that pushdowns miss, making them key for complete triceps and arm size.
Why do skull crushers hurt my elbows?
Usually flaring elbows or too much weight — keep elbows tucked and control the weight; some people also just need an EZ-bar or a different exercise.
Should I lower to my forehead or behind my head?
Both work; behind the head increases the long-head stretch and is often easier on the elbows.
Skull crushers or pushdowns?
Both — skull crushers for the long head (arms overhead), pushdowns for the other heads (arms down).
What bar should I use?
An EZ-bar is easiest on the wrists and elbows; dumbbells offer a natural path.
How many reps?
Moderate reps (8–12) with controlled form suit this exercise.
Skull crushers train the long head your pushdowns ignore. Keep your elbows in, control the weight, and the name stays a metaphor.
Skull crushers are one of the best triceps builders because they hit the long head that pushdowns leave behind. Keep your elbows tucked, control every rep, and use an EZ-bar or adjust the path if your elbows complain. Pair them with pushdowns for complete triceps, and you'll build the arm size that comes from training all three heads — not just the two everyone else does.