Skull Crusher (Modified)
The modified skull crusher is performed lying on the floor, where the mats set a natural depth stop and the elbows can rest between reps if needed. The shortened, safer range makes it the right first version for beginners learning to keep upper arms still while the elbows hinge under load. Coached by Maddy (NASM-CPT) — these are the exact form cues he gives on every client's first week.
Muscles worked
Sets & reps by goal
| Goal | Sets × Reps | Rest |
|---|---|---|
| Strength | 4 × 4–6 | 2 min |
| Muscle | 3–4 × 9–12 | 60–90 s |
| Endurance | 3 × 15–20 | 45–60 s |
Rep ranges per Helms 2014 · Schoenfeld 2016.
Level — Beginner
The training-wheels version of the lying extension — same skill, with the floor setting both the safety net and the range.
Proper form — 5 cues
- Lie on the floor, knees bent, dumbbells pressed to arms vertical
- Set the upper arms still, angled a touch toward your head
- Lower the dumbbells until the backs of the upper arms approach the floor
- Touch down softly — or hover just above — then extend to straight
- Reset the upper-arm position every few reps as fatigue builds
Breathing: Breathe in as the elbows fold down, breathe out driving the weights to straight.
The 3 mistakes Maddy corrects most
Common questions
What makes the floor skull crusher easier than the bench version?
The floor acts as a built-in safety net and depth gauge: the elbows can only travel so far, the stretch cannot be overshot, and any lost rep simply rests on the ground. Beginners can learn the fixed-upper-arm skill without the anxiety of a free-hanging weight above their face.
Can I build real triceps size with the floor version?
Yes — the elbow-extension work is genuine, and for new lifters the loadable range is more than enough to drive growth for months. The bench version eventually offers a deeper stretch, which becomes worth pursuing once your control is automatic and your working weights outgrow the floor's range.
How light should I start with modified skull crushers?
Lighter than feels impressive — 2 to 5 kg per dumbbell for most beginners. The skill being learned is a motionless upper arm, and heavy weights teach the opposite by recruiting the shoulders to swing. When ten slow reps feel crisp and the upper arms never wander, add the next small increment.
Related exercises
Harder: Skull Crusher
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