Tricep Exercise Tweak: How to Fix Your Skull Crushers for Better Results
Summary
Jeff Cavalier of AthleanX breaks down the skull crusher (lying tricep extension), arguing that 90% of gym-goers perform it incorrectly by finishing the movement in the wrong arm position. By making one small adjustment — keeping the arms angled slightly backward at the top of the rep — you maintain continuous tension on the triceps throughout the entire set.
Key Points
- The most common mistake in the skull crusher is finishing the rep with arms fully vertical, which shifts the load away from the triceps entirely
- When arms are locked out vertically, the biceps activate to hold the bar in place — and because of reciprocal inhibition, a contracting bicep means a relaxed tricep
- To keep the triceps under load, arms should angle slightly backward past vertical at the top of each rep
- A variation that allows a more vertical arm position is a hybrid movement combining the close-grip bench press and the tricep extension — the bar tilts toward the chest at the bottom, then presses straight back up
- Maintaining continuous tension on the muscle is directly linked to time under tension, which is a key driver of muscle hypertrophy
- Resting the muscle mid-set by landing in the wrong top position breaks the tension window and reduces the effectiveness of the exercise
- Efficient, correctly performed exercises are the reason short 30–40 minute workouts can outperform longer, poorly executed sessions
Exercise Details
Skull Crusher (Lying Tricep Extension)
Target Muscles
- Primary: Triceps (all three heads, with emphasis on the long head due to the overhead stretch position)
Equipment Options
- EZ curl bar, straight barbell, or dumbbells
Proper Form Cues
- Lie flat on a bench and start with arms angled slightly behind vertical, not straight up
- Lower the bar toward your forehead/nose in a controlled arc
- Extend back up while maintaining that backward arm angle at the top — never let arms go fully perpendicular to the floor
- The tricep should be under tension throughout the entire range of motion
Common Mistakes to Avoid
- Finishing the rep with arms straight up toward the ceiling — this offloads the tricep and loads the bicep
- Allowing the muscle to “rest” at the top of each rep by reaching a mechanically passive lockout position
Hybrid Skull Crusher / Close-Grip Press Variation
How to Perform
- Begin with arms extended vertically (straight overhead)
- As you lower the weight, allow the dumbbell or bar to tilt down toward the chest, mimicking the bottom of a close-grip bench press
- Press back up to the straight-arm position
- This version legitimizes the vertical arm position by converting the lockout into the active pressing phase of a compound movement
Why It Works
- Combines the tricep extension stretch at the bottom with the pressing mechanics of a close-grip press
- Keeps the triceps engaged through a longer, more complete range of motion
Sets/Reps
- No specific sets or reps prescribed, but Jeff references targeting approximately 45 seconds of time under tension per set as a guiding principle for muscle growth