Single-Arm Dumbbell Skull Crusher
The single-arm dumbbell skull crusher is an elbow extension lying on a flat bench, with one upper arm vertical and the dumbbell lowering toward the ear, that isolates the triceps and lets you even out strength between sides.
TRICEPS · PUSH
How it is executed
- Lie back on a flat bench holding one dumbbell straight over your shoulder with a neutral or pronated grip.
- Keeping your upper arm vertical and still, bend only at the elbow to lower the dumbbell toward the same-side ear or shoulder.
- Feel the triceps stretch, then extend your elbow to return to the top under control.
- Working one arm at a time lets you focus on a full range and even out strength differences between sides.
Common mistakes
- Letting the elbow flare out. With a single dumbbell the upper arm tends to drift toward the side and the triceps loses tension. Point the elbow at the ceiling and, if needed, hold the upper arm with the free hand.
- Moving the upper arm toward the chest on the way up. If the elbow travels forward, the exercise turns into a press and the chest helps. Keep the upper arm vertical or tilted slightly toward the head: only the forearm moves.
- Cutting the lowering phase short. Out of fear of the dumbbell, many stop with the elbow at 90 degrees and miss the stretch on the long head. Lower to ear level or a little past it, with a load you can brake.
- Lifting the shoulder off the bench to help. With the load on one side only, the torso tends to roll toward that arm and the chest joins the push. Keep both shoulders on the bench and the feet planted on the floor.
Frequently asked questions
- Which muscles does the single-arm dumbbell skull crusher work?
- The triceps brachii does all the work: its three heads extend the elbow, and the long head, which also crosses the shoulder, is stretched further when the upper arm tilts slightly toward the head. The lats and rear deltoid work isometrically to stop the arm from drifting back as the dumbbell lowers, and the forearm holds the load. The abs keep the lower back on the bench.
- Single-arm skull crusher or both dumbbells at once: when should you choose each?
- Go single-arm when one side pushes harder than the other or your elbow flares: the free hand can hold the upper arm and fix the path, and each triceps does its own work without the stronger side compensating. With both dumbbells at once you save time and can load a bit more, so it is the option for accumulating volume once the technique is solid. For heavy sets, an EZ bar allows more weight with a fixed grip.
- How many sets and reps of the single-arm dumbbell skull crusher should you do?
- A common starting point is 3 sets of 8 to 12 reps per arm, leaving 1 to 3 reps in reserve. Start with the weaker arm and match that number of reps with the other one, even if it has more in the tank. It usually comes after the presses, with the triceps already warm, and before or instead of cable extensions. If the last rep comes up with the elbow flaring, lower the load.
- Where should the dumbbell go: to the forehead, the ear or behind the head?
- With a single dumbbell and a neutral grip, the natural path is beside the head, at ear level: the forearm passes next to the face and the elbow keeps pointing at the ceiling. If you tilt the upper arm a few degrees back and lower behind the head, the long head stretches more and tension does not disappear at the top. Lowering to the forehead, with the arm vertical, is the version with the least stretch.
Sources and editorial approach
The explanation, variations and FAQs are Kaizer’s editorial synthesis. ACSM’s 2026 guidance provides general context on progression and resistance training in healthy adults; it does not independently validate the technique of each variation.
No individual professional review is recorded for this page.
Variations and substitutions
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