Dumbbell Skullcrusher
The dumbbell skullcrusher, also called a lying triceps extension, isolates the triceps by bending only at the elbow while lying on a bench. Two dumbbells replace the usual barbell or EZ-bar, letting each arm move through its own natural path while your triceps handle nearly all of the work.
Why it works
The triceps has one main job across all three of its heads: straighten the elbow. Lying down and keeping the upper arms still removes the shoulders from the movement almost entirely, so the elbow-extension motion falls squarely on the triceps instead of getting shared with the chest or shoulders the way a close-grip bench press would share it. That isolation is exactly why the skullcrusher tends to build the lockout strength that carries over to pressing movements like the bench press and shoulder press.
Set up
- Lie back on a flat bench with a dumbbell in each hand, arms extended straight up over your chest.
- Turn your palms to face each other, keeping the dumbbells close together.
- Plant your feet flat on the floor for stability.
- Keep your upper arms vertical and still; only your forearms will move.
How to do it
- Bend your elbows and let the dumbbells travel down near your temples, keeping your upper arms fixed in place.
- Stop just before the dumbbells reach your head, or when you feel a full stretch in the triceps.
- Pause briefly at the bottom without letting your elbows drift outward.
- Extend your elbows to press the dumbbells back up to the starting position.
- Keep the motion isolated to the elbow joint throughout the entire set.
Form cues
- Elbows stay fixed, only the forearms move.
- Lower toward your temples, not your chest.
- Keep elbows tucked in, not flared out to the sides.
- Full extension at the top without slamming the elbows straight.
Breathing: Inhale as you lower the dumbbells toward your head, exhale as you press them back up.
Common mistakes
Letting the upper arms drift backward toward the face as the elbows bend.
Fix: Keep your upper arms vertical and still throughout the set; only the forearms should travel.
Flaring the elbows out to the sides instead of keeping them pointed toward the ceiling.
Fix: Keep your elbows tracking straight up and down, tucked closer to a shoulder-width position.
Using too much weight and turning the movement into a partial-range press.
Fix: Lighten the load until you can lower the dumbbells through a full, controlled range without your shoulders taking over.
Rushing the lowering phase and losing control near your head.
Fix: Slow down the descent, especially in the last few inches, since this is where the risk of losing control is highest.
How to program it
- Two or three sets of 8 to 12 reps works well as a targeted triceps finisher after a pressing movement.
- As a single-joint isolation exercise, training it two or three times a week is reasonable if your elbows feel good.
- Because control near the head matters more than load here, add weight gradually and only once the full range feels stable.
- Fits naturally at the end of a chest or shoulder day, since your triceps are usually already warmed up from pressing.
Safety notes
- Use a spotter or start with lighter dumbbells until you're confident controlling the bottom position near your head.
- Stop the descent higher up if you feel any elbow discomfort, and build the range back up gradually over time.
Exercise profile
- Force
- Push
- Mechanics
- Isolation
- Category
- Strength
Frequently asked questions
How many sets and reps for dumbbell skullcrushers?
Two or three sets of 8 to 12 reps is a solid range for building triceps strength and size with this exercise.
Are dumbbell skullcrushers safe?
They're safe with a controlled range and appropriate weight. The main risk is losing control near your head, so start lighter than you think you need and build up once the movement feels stable.
Skullcrusher or tricep extension, what's the difference?
They train the same muscle through a similar bending motion; the skullcrusher usually refers to the lying version done to a point near the head, while standing or overhead tricep extensions change the body position and the angle of stretch on the triceps.
What can I use instead of dumbbells for skullcrushers?
An EZ-bar or straight barbell works for the same movement pattern and often feels more stable since both arms move together.