reckonerDumbbell skullcrusher
A lying triceps extension with a dumbbell in each hand instead of a bar. The bells let your wrists and forearms sit where they want to, which is most of the reason people who cannot do this with a barbell can do it with these.
Only the forearms move, elbows still.
- Pattern
- Arm isolation
- Trains
- Triceps
- Kit
- Dumbbell, bench
- Loading
- A weight you choose
- Reckoner prescribes
- 3 sets of 10 to 15 reps at RPE 8
- Progression step
- 1 kg once the top of the range is clean
- Skill
- Some technique
- Recovery cost
- Low
- Not prescribed if you have declared
- Elbow
Muscles worked
How to do it
Set up flat with the bells over your shoulders
Lie back with a bell in each hand, palms facing each other, arms straight and stacked over the shoulder joints rather than over your face. Feet flat, ribs down. Get the start position right lying down, because you cannot fix it once the set has begun.
Bend at the elbow and nowhere else
Only the forearms move, elbows still. That is the cue on your wrist and it is the entire technique. The upper arms hold their angle for every rep of every set.
Lower to beside the head, not to the forehead
With dumbbells you can take the bells past your ears instead of stopping at the skull, which is the one real advantage they have over a bar. Go until the triceps are stretched and your elbows are still where you left them.
Press back to straight and keep the tension
Drive the bells back up to the start without letting the arms drift back over your face to rest. If you find yourself pausing at the top, the set has more in it than the position does.
What goes wrong
Turning it into a press
The upper arms swing back toward the head on the way down and forward on the way up, and the lift becomes a clumsy dumbbell press with a longer arc. It is the standard failure and it always arrives with the weight, not with the fatigue.
Letting the elbows drift toward the hips
Point the elbows at the ceiling and keep them there. Once they slide down toward your feet the lats start pulling and you are doing a narrow pullover with a bend in the arm.
Judging the movement by the number on the bells
Lying with the upper arms vertical puts the shoulder between the two positions that have actually been compared, arms overhead and arms by the side2, so the loads that work here sit between a press-down's and an overhead extension's. Reading the position that way is reasoning rather than a result: nobody has run the skullcrusher against either of them.
How Reckoner progresses this lift
Six weeks of this lift, from 10 kg, run through the real engine. Nothing below was typed in: the prescription, the decision and the sentence beside it all come from the same code that writes your week.
| Week | Prescribed | What it did |
|---|---|---|
| 1 | 3 x 10 at 10 kg | More reps 10 → 11 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 2 | 3 x 11 at 10 kg | More reps 11 → 12 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 3 | 3 x 12 at 10 kg | More reps 12 → 13 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 4 | 3 x 13 at 10 kg | More reps 13 → 14 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 5 | 3 x 14 at 10 kg | Deload 40% of sets offFive weeks of building, then one week lighter. About 40% of the sets come off. The load holds and your reps stay where you earned them, so you keep the strength and lose the fatigue. |
| 6 | 2 x 14 at 10 kg | More reps 14 → 15 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. The lighter week is over, so this is back to three sets. |
Real engine output, not an illustration. Every row was produced by running the engine itself when this page was generated.
The full rule, and why the reps move before the load does, is in how Reckoner decides to add weight.
Questions people ask
Do I have to lower all the way down?
The honest answer is that this is not settled, and the one trial run on this exact movement points the opposite way from the usual advice. Forty four trained men did barbell lying triceps extensions three times a week for eight weeks, one group over a restricted range and one over the full range, and the restricted range group gained more triceps cross-sectional area, 48.7 per cent against 28.2 per cent1. That is a single study with a large effect and it has not been replicated. Lower as far as your elbows are comfortable holding position, and do not cut the range in order to add weight.
Dumbbells or a barbell?
No trial has compared them, so this is a question about your joints rather than about hypertrophy. The difference is the grip: a straight bar fixes your forearms in one rotation and the bells do not, and an EZ bar sits between the two. If the barbell version puts a line of pain across the inside of your elbow, the bells are the version to keep.
What does Reckoner do when this lift stalls?
It eases the load first and lets you rebuild toward the weight that stopped moving. Only a second stall after that reset gets you an offer of something else from the group below.
Similar movements
Reckoner eases the load first when this lift stalls, and offers one of these only if it stalls again after that. A lift already as light as your kit goes has no load left to ease, so the offer comes straight away. Each of them has a page.
Sources
- Goto and colleagues, Journal of Strength and Conditioning Research, 2019. Partial range of motion exercise is effective for facilitating muscle hypertrophy and function through sustained intramuscular hypoxia in young trained men forty four trained men doing barbell lying triceps extensions for eight weeks, the restricted range group gaining 48.7 per cent triceps cross-sectional area against 28.2 per cent for the full range group
- Maeo and colleagues, European Journal of Sport Science, 2023. Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position the two arm positions that have been compared directly, overhead against neutral, and the lower absolute loads the overhead position takes