Skull Crushers: Targeted Muscles, Benefits, and Proper Execution

What do skull crushers target?

Skull crushers primarily target the triceps brachii muscle group, specifically emphasizing the long head due to the shoulder's extended position, while also engaging synergistic muscles for stability and support during the elbow extension movement.

Understanding the Triceps Brachii

The triceps brachii, meaning "three-headed arm muscle," is the large muscle on the posterior aspect of the upper arm. It is crucial for elbow extension and plays a significant role in shoulder stability. Its three distinct heads are:

• Long Head: Originates from the infraglenoid tubercle of the scapula (shoulder blade). Due to its origin across the shoulder joint, it assists in shoulder extension and adduction.
• Lateral Head: Originates from the posterior surface of the humerus, superior to the radial groove. It is primarily involved in elbow extension.
• Medial Head: Originates from the posterior surface of the humerus, inferior to the radial groove. It is the workhorse of the triceps, active in all elbow extension movements, and is often the last head to fatigue.

All three heads converge to insert via a common tendon onto the olecranon process of the ulna (forearm bone).

Primary Muscle Targeted: The Triceps Brachii

The skull crusher is an isolation exercise designed to place maximal tension on the triceps brachii.

• Emphasis on the Long Head: The unique aspect of the skull crusher, particularly when performed with the upper arms slightly angled back (shoulder extension), is the stretch and subsequent activation of the long head of the triceps. Because the long head crosses both the shoulder and elbow joints, positioning the humerus in extension (i.e., the bar is lowered towards or behind the head) stretches the long head, pre-fatiguing it and enhancing its contribution to the elbow extension phase.
• Comprehensive Triceps Engagement: While the long head receives significant emphasis, both the lateral head and medial head are also heavily recruited to execute the powerful elbow extension required to lift the weight. The medial head is active throughout the entire range of motion, providing consistent force, while the lateral head contributes significantly, especially during heavier lifts.

Synergistic and Stabilizer Muscles

While the triceps are the prime movers, several other muscles contribute to the execution and stability of the skull crusher:

• Anconeus: A small muscle located near the elbow joint, the anconeus assists the triceps in elbow extension, particularly at the end range of motion.
• Deltoids (Anterior): The front portion of the shoulder muscles helps stabilize the shoulder joint, preventing unwanted movement of the humerus as the triceps contract.
• Pectoralis Major/Minor: While not directly involved in the movement, the chest muscles contribute to the overall stability of the upper body, especially when performed on a bench.
• Forearm Flexors and Extensors: Muscles in the forearms work isometrically to maintain a stable grip on the barbell or dumbbells, ensuring control of the weight throughout the exercise.

Biomechanics of the Skull Crusher

The skull crusher is primarily an open kinetic chain exercise focusing on elbow extension.

• Elbow Joint Action: The concentric (lifting) phase involves powerful extension of the elbow joint against resistance. The eccentric (lowering) phase involves controlled flexion of the elbow joint, placing the triceps under stretch.
• Shoulder Joint Stability: Unlike exercises like the close-grip bench press, where the shoulder joint undergoes significant movement, the skull crusher aims to keep the upper arm relatively stationary, isolating the movement to the elbow joint. Maintaining this stability is crucial for effective triceps targeting and injury prevention.

Benefits of Incorporating Skull Crushers

Including skull crushers in a training regimen offers several advantages:

• Triceps Hypertrophy: The direct and isolated nature of the exercise makes it highly effective for building size and strength in all three heads of the triceps.
• Improved Pressing Strength: Stronger triceps directly translate to improved performance in compound pressing movements such as bench press, overhead press, and dips.
• Elbow Joint Health: When performed with proper form and appropriate weight, skull crushers can contribute to the strength and stability of the elbow joint.
• Aesthetic Development: Well-developed triceps contribute significantly to the overall size and appearance of the upper arm, making the arm look fuller from both front and side profiles.

Proper Execution and Safety Considerations

To maximize triceps activation and minimize injury risk:

• Controlled Movement: Always use a controlled tempo, especially during the eccentric (lowering) phase, to maintain tension on the triceps and protect the elbow joints.
• Appropriate Weight: Start with a lighter weight to master the form. Using excessive weight can compromise technique, place undue stress on the elbows, and shift tension away from the triceps.
• Wrist Position: Keep wrists straight and neutral to avoid unnecessary strain.
• Arm Angle: Maintain the upper arms perpendicular to the torso or slightly angled back to effectively target the long head. Avoid letting the elbows flare out excessively.
• Spotter/Safety: When using a barbell, especially with heavier loads, consider having a spotter or using safety pins if performing in a power rack.

Variations and Alternatives

While the traditional barbell skull crusher is effective, variations can offer different stimuli or accommodate individual needs:

• Dumbbell Skull Crushers: Allows for independent arm movement, addressing muscular imbalances.
• EZ Bar Skull Crushers: The angled grip can be more comfortable for some individuals' wrists.
• Incline/Decline Skull Crushers: Alters the angle of resistance and can slightly shift emphasis.
• Cable Skull Crushers: Provides constant tension throughout the range of motion.

Alternatives that also heavily target the triceps include close-grip bench presses, overhead triceps extensions, and various triceps pushdown variations.