Skull Crushers: Build Bigger, Stronger Triceps with This Classic Arm-Day Staple

If someone walked up to you at the gym and casually asked, "Wanna do some skull crushers?", you might take a step back—understandably. But don’t let the name scare you off. The skull crusher, also known as a lying triceps extension, is a foundational triceps-building movement that’s been a go-to for lifters looking to grow stronger, more defined arms.

Simple in setup but demanding in execution, skull crushers deliver targeted isolation to all three heads of the triceps. In this guide, we’ll explore how to do them correctly, the muscles worked, the benefits, and why this movement still deserves a place in your push-day routine.

What Are Skull Crushers?

The skull crusher is a triceps isolation exercise traditionally performed lying on a bench while extending and flexing the elbows under load. The movement gets its ominous name from the barbell’s path—lowering toward the forehead before being extended back to the lockout position.

You can perform skull crushers with a barbell, EZ bar, dumbbells, or cables, depending on your goals and training equipment. While it’s not always the most beginner-friendly movement due to elbow strain potential, it's extremely effective when done with proper control and technique.

“Lying triceps extensions activate the long head of the triceps more effectively than standard pushdowns and are ideal for improving upper arm size and strength.” — Saeterbakken et al., European Journal of Sport Science

Muscles Worked in Skull Crushers

The skull crusher is designed to isolate the triceps brachii, which has three distinct heads:

1. Long Head

• Originates on the scapula and plays a major role in overhead extension and full elbow lockout.

• This head is particularly activated when the arms are overhead—making skull crushers highly effective.

2. Lateral Head

• Positioned on the outer part of the upper arm.

• Contributes to the “horseshoe” shape of well-developed triceps.

3. Medial Head

• Lies deeper beneath the long and lateral heads.

• Provides elbow extension support and contributes to pressing endurance.

Secondary Muscles Activated:

• Pectoralis Major (Chest)

• Anterior Deltoid (Shoulder)

• Forearms (Stabilizers)

These assist mainly during the lockout phase of the movement, especially when heavier loads are involved.

Benefits of Skull Crushers

1. Isolates the Triceps

Unlike pressing movements where the chest and shoulders often take over, skull crushers minimize involvement from other muscles, allowing the triceps to do the majority of the work.

2. Increases Arm Size

Adding skull crushers to your arm training routine can dramatically improve the overall thickness and shape of the upper arm, particularly when paired with compound push exercises.

“Triceps contribute approximately two-thirds of total upper arm mass, making triceps-specific training key for overall arm development.” — Del Monte, NSCA Performance Training Journal

3. Improves Lockout Strength

Struggling with bench press or overhead press lockout? Skull crushers improve elbow extension strength, making them an ideal accessory movement to enhance compound pressing performance.

4. Promotes Muscle Balance

Training the triceps in isolation ensures they aren’t overshadowed by chest and shoulder development—important for injury prevention and joint health.

How to Do Skull Crushers (Step-by-Step)

The following instructions apply to the EZ bar skull crusher, one of the most joint-friendly and popular variations.

1. Setup

   • Lie flat on a bench with a loaded EZ bar (or barbell) held in a shoulder-width grip.

   • Extend the arms so the bar is directly over your shoulders.

2. Brace and Position

   • Plant your feet on the floor and lightly retract your shoulder blades.

   • Keep your elbows pointed upward—do not let them flare outward.

3. Lower the Bar

   • Bend the elbows to slowly lower the bar toward your forehead or just behind the crown of your head.

   • Keep the upper arms stationary—only the forearms should move.

4. Stretch and Control

   • Stop once you feel a comfortable stretch in the triceps—about 1–2 inches above your forehead or behind your head.

   • Do not let the bar drift too far forward, which increases injury risk.

5. Press and Extend

   • Reverse the movement by forcefully extending the elbows and returning the bar to the starting position.

   • Squeeze the triceps at the top, ensuring full elbow extension.

6. Repeat

   • Perform for the prescribed number of reps, maintaining strict form throughout.

Pro Tip: Lowering the bar slightly behind the head (instead of directly to the forehead) increases stretch on the long head while reducing wrist strain.

Common Mistakes to Avoid

• Letting the Elbows Flaring Outward
  This reduces tension on the triceps and transfers load to the chest and shoulders.

• Using Too Much Weight
  Skull crushers are best performed with moderate loads and higher rep ranges. Too much weight increases joint stress and disrupts form.

• Not Controlling the Eccentric
  Dropping the bar quickly or bouncing out of the bottom puts unnecessary stress on the elbows and connective tissues.

• Shortening the Range of Motion
  Failing to lower the bar fully or cut the lockout short reduces muscle activation and hypertrophy potential.

• Overreliance on Momentum
  Keep the movement slow and controlled. If your hips are shifting or your back is arching excessively, the weight is likely too heavy.

Programming Skull Crushers

Skull crushers work best as an accessory lift following compound pressing movements or as a main isolation exercise in an arm-specific split.

Try pairing skull crushers with:

• Dips

• Overhead Triceps Extensions

• Cable Pushdowns

• Close-Grip Bench Press

This pairing creates a well-rounded triceps-focused workout that hits all angles and heads.

Variations of the Skull Crusher

• Dumbbell Skull Crushers: Greater range of motion and independent arm loading.

• Barbell Skull Crushers: Better for heavier loads, but more strain on elbows.

• Cable Skull Crushers: Constant tension and reduced joint strain.

• Incline Skull Crushers: Emphasizes the long head with an extended arm position.

• Smith Machine Skull Crushers: Controlled path, ideal for hypertrophy-focused training.

Final Thoughts: Should You Be Doing Skull Crushers?

The skull crusher is a time-tested triceps builder—one that isolates the back of the upper arms like few other exercises can. While it requires attention to form and should be approached with caution regarding elbow stress, it delivers undeniable results in size, strength, and pressing performance when programmed correctly.

Start with lighter weights, master your technique, and work within a controlled range of motion. Once you build confidence, it’s a powerful addition to any upper body push routine.

“Triceps-focused exercises like skull crushers are essential for complete upper-body strength and performance enhancement.” — Schoenfeld, Journal of Strength and Conditioning Research

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