Exercises / Skull Crusher
Skull Crusher
The skull crusher is a barbell isolation movement that trains triceps first. Default rest between sets in the app: 90 s (1½ min).
Also called: lying triceps extension.
Rep and RIR targets by goal
These are the sets the Zyra Workouts program generator writes for a isolation exercise under each goal. RIR is reps in reserve — how many more reps you could have done when the set ended. A default the app starts from, not a prescription.
| Goal | Reps per set | RIR | Rep ceiling |
|---|---|---|---|
| Strength | 6–8 | 2 | 9 |
| Hypertrophy | 10–15 | 1 | 14 |
| General | 8–12 | 2 | 12 |
How progression steps on Skull Crusher
The app moves the load on Skull Crusher in steps of 2.5 kg — two of the smallest plate in the default inventory (1.25 kg per side). The rule is the same for every exercise: the rep ceiling is the midpoint of the rep range plus the RIR target (for the hypertrophy row here, 10–15 reps @ RIR 1 → ceiling 14). Clear the ceiling and the next set is one step heavier at the bottom of the range; fall under the range floor and it backs off one step; anything between holds.
Worked example, in the app's words: Last time 40 kg × 15 · target 10–15 @RIR 1 (ceiling 14) → +2.5 kg → 42.5 kg × 10.
Alternatives
Tools for this exercise: Skull Crusher 1RM calculator · Skull Crusher load chart (% of 1RM)
Frequently asked
What muscles does the skull crusher work?
In the Zyra Workouts catalog the skull crusher is tagged with triceps as its primary muscle and no secondary muscles. The app counts a primary set as one set for that muscle and a secondary set as half a set. Which muscles a lift loads most also depends on technique and range of motion.
How many reps and sets for the skull crusher?
The app's program generator sets 6–8 reps @ RIR 2 for strength, 10–15 reps @ RIR 1 for hypertrophy, 8–12 reps @ RIR 2 for general — the isolation rule, 2–4 sets depending on goal and experience. These are the generator's defaults, not a prescription; a coach can adjust them to you.
What can I do instead of the skull crusher?
The app's swap ranking (same primary muscle, then feasible in your gym, same type, same equipment) offers Overhead Tricep Extension, Tricep Pushdown, Close-Grip Bench Press and Tricep Dip (Upright). All train triceps first.
Muscle groups
- Triceps — counts as a full set
None listed in the catalog.
Related exercises
Other arms movements in the catalog:
Guides for Skull Crusher
Log it in Zyra Workouts
Zyra Workouts logs your sets on the skull crusher, applies this progression rule to suggest the next load, and counts the work toward your weekly sets per muscle — offline-first, on iOS. It is in development and not yet on the App Store.
Zyra is a training and nutrition tracking tool. Nothing on this page is medical advice, a diagnosis, or an individual prescription. The numbers are estimates from published formulas and the apps' own rules — consult a qualified professional for decisions about your health, and a coach for your training.