# Single Arm Dumbbell Skull Crusher

A one-arm lying triceps extension with a dumbbell on a flat bench, the free hand holding the working upper arm in place. Trains the triceps one side at a time.

- Beginner · Isolation
- Equipment: Dumbbells, Flat bench
- HD video: https://media.seto.fit/exercises/dumbbell-lying-one-arm-neutral-triceps-extension/video/male.mp4
- HTML: https://seto.fit/exercises/single-arm-dumbbell-skull-crusher/

## Muscles worked

- Triceps: 10/10
- Forearms: 3/10
- Rotator Cuff: 3/10

## How to do the Single Arm Dumbbell Skull Crusher

1. Lie on a bench, feet flat, one dumbbell above your shoulder.
2. Hold the working upper arm with your free hand, elbow pointing up.
3. Bend your elbow to lower the dumbbell beside your head.
4. Straighten your arm back up, then switch arms after all reps.

### Full technique — 7 steps

1. Lie on a flat bench with feet planted and one dumbbell held above your shoulder.
2. Use a neutral grip and set your upper arm nearly vertical with the elbow pointing upward.
3. Hold the working upper arm near the elbow with your free hand.
4. Bend your elbow to lower the dumbbell beside your head.
5. Stop when your elbow is fully bent and your upper arm has stayed in place.
6. Extend your elbow to drive the dumbbell back up until your arm is straight over your shoulder.
7. Finish all reps on one side, then switch arms and repeat.

## Common mistakes

- Upper arm drifting backward
- Turning it into a press
- Cutting the bottom range short
- Stopping short of full extension
- Pushing the arm with the free hand

## Form cues

- Lower beside the head
- Use a neutral grip
- Keep upper arm vertical
- Hold arm with free hand
- Straighten arm completely

## How much to do

- **Strength**: 3–4 sets of 6–8 reps · rest 1 min 30 s · 2–3 reps in reserve · lower 3 s, lift 1 s
- **Muscle growth** (best fit): 3–4 sets of 8–12 reps · rest 1 min · 2–3 reps in reserve · lower 3 s, lift 1 s
- **Endurance** (good fit): 2–3 sets of 15–20 reps · rest 45 s · 3–4 reps in reserve · lower 2 s, lift 1 s

Reps in reserve: how many more you could still do when you end the set.

## Substitutes by equipment

Same muscles, same movement — pick the version you have the gear for.

- **Resistance bands**: [Resistance Band Floor Skull Crusher](https://seto.fit/exercises/resistance-band-floor-skull-crusher/), [Single Arm Overhead Resistance Band Triceps Extension](https://seto.fit/exercises/single-arm-overhead-resistance-band-triceps-extension/)
- **Cable machine**: [Triceps Pushdown (Reverse Grip)](https://seto.fit/exercises/triceps-pushdown-reverse-grip/), [Cable Overhead Triceps Extension (EZ Bar)](https://seto.fit/exercises/cable-overhead-triceps-extension-ez-bar/)
- **Kettlebell**: [Kettlebell Overhead Triceps Extension](https://seto.fit/exercises/kettlebell-overhead-triceps-extension/), [Kettlebell Skull Crusher](https://seto.fit/exercises/kettlebell-skull-crusher/)
- **Barbell**: [Barbell Skull Crusher](https://seto.fit/exercises/skull-crusher-barbell/)

## Where to start and where to go next

Same muscles, same movement. Too hard for now — step down; once it gets easy — step up.

- **This exercise: Single Arm Dumbbell Skull Crusher — Beginner**
- Harder: [Dumbbell Overhead Triceps Extension](https://seto.fit/exercises/overhead-triceps-extension-dumbbell/) — Beginner
- Harder: [Dumbbell Skull Crusher](https://seto.fit/exercises/skull-crusher-dumbbell/) — Intermediate

## Quick answers

### What muscles does the Single Arm Dumbbell Skull Crusher work?

Primary: Triceps 10/10. Also works: Forearms 3/10, Rotator Cuff 3/10.

### When should I do the Single Arm Dumbbell Skull Crusher in a workout?

Finisher. Goes last, once the heavy work is done. ≈ 8 min with rest.

### How many sets and reps of the Single Arm Dumbbell Skull Crusher?

Strength: 3–4 sets of 6–8 reps, rest 1 min 30 s, 2–3 reps in reserve. Muscle growth: 3–4 sets of 8–12 reps, rest 1 min, 2–3 reps in reserve. Endurance: 2–3 sets of 15–20 reps, rest 45 s, 3–4 reps in reserve.

### What can I do instead of the Single Arm Dumbbell Skull Crusher?

Resistance bands: Resistance Band Floor Skull Crusher, Single Arm Overhead Resistance Band Triceps Extension. Cable machine: Triceps Pushdown (Reverse Grip), Cable Overhead Triceps Extension (EZ Bar). Kettlebell: Kettlebell Overhead Triceps Extension, Kettlebell Skull Crusher. Barbell: Barbell Skull Crusher.

### What is a harder version of the Single Arm Dumbbell Skull Crusher?

Dumbbell Overhead Triceps Extension (Beginner), Dumbbell Skull Crusher (Intermediate).

How we rate exercises: https://seto.fit/guides/methodology/

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