Skull Crusher Exercise

The Skull Crusher is a popular strength-training exercise that primarily targets the triceps, the large muscles located on the back of the upper arm. Although the name sounds intimidating, the exercise is completely safe when performed with proper technique. The name comes from the fact that the weight is lowered toward the forehead before being pressed back up.

To perform a Skull Crusher, lie flat on a workout bench while holding an EZ curl bar, barbell, or dumbbells directly above your chest. Keep your arms straight and your elbows pointing upward. Slowly bend your elbows and lower the weight toward your forehead or slightly behind your head. Once you feel a stretch in your triceps, extend your arms back to the starting position.

Unlike many compound exercises, the Skull Crusher mainly isolates the triceps. This makes it one of the best exercises for increasing arm size and improving pushing strength used in movements such as bench presses, push-ups, and shoulder presses.

Muscles Activated During Skull Crushers

Several muscles work together during the movement, but the triceps are the primary focus.

• Triceps Brachii (Primary Muscle)

  The triceps brachii is the largest muscle located at the back (posterior) of the upper arm. It is named "tri-ceps" because it consists of three heads: the Long Head, Lateral Head, and Medial Head. Together, these three heads work to extend (straighten) the elbow joint. The triceps make up approximately 60–70% of the arm's total size; therefore, training the triceps is crucial for achieving large, muscular arms.

  • Long Head

  The Long Head is the longest and most unique part of the triceps. It is the only one of the three heads that crosses both the shoulder joint and the elbow joint. It originates from the infraglenoid tubercle of the scapula (shoulder blade) and, along with the other heads, inserts onto the olecranon process of the ulna. The primary function of the Long Head is elbow extension; however, because it crosses the shoulder joint, it also assists in shoulder extension and adduction. The Long Head becomes active when you move your arm backward (such as during a swimming stroke or a rowing movement). Consequently, the Long Head is considered not just a triceps muscle but also a shoulder stabilizer.
  
  From an aesthetic standpoint, the Long Head contributes significantly to the overall mass of the triceps. It plays a major role in the thickness visible when viewing the arm from the side. A well-developed Long Head makes the arm appear larger and denser. During training, the Long Head undergoes the greatest stretch when the arm is positioned overhead. For this reason, exercises such as Overhead Dumbbell Extensions, Overhead Cable Extensions, and French Presses (a variation of the Skull Crusher) are considered highly effective for targeting the Long Head. The overhead position provides a deep stretch to the muscle, which can enhance the stimulus for hypertrophy.
  
  The Long Head also contributes to shoulder stability, supporting the shoulder joint during heavy pressing exercises like the bench press or dips. For athletes—particularly throwers and swimmers—the strength of the long head is crucial for both performance and injury prevention. If an athlete's long head is weak, both power and control during overhead movements can be compromised.

  • Lateral Head

  he lateral head is often referred to as the "horseshoe" head of the triceps because, when well-developed, it creates a prominent shape on the outer side of the arm. This head originates from the upper region of the posterior surface of the humerus (upper arm bone) and attaches to the ulna via the common triceps tendon. The lateral head is considered relatively rich in fast-twitch muscle fibers. This means it is highly active during explosive, high-force movements. When pushing heavy weights or performing powerful extension movements, recruitment of the lateral head increases significantly.
  
  The primary function of this head is elbow extension. Whenever you perform pushing movements—such as bench presses, push-ups, dips, or close-grip bench presses—the lateral head plays a significant role in force production. It is particularly active when the resistance is heavy and the movement is powerful.
  
  From a bodybuilding and aesthetic perspective, the lateral head enhances the arm's outer width. When the lateral head is well-developed, the arm appears wider and more impressive from both front and side angles. Competitive bodybuilders pay special attention to this head to accentuate the triceps' horseshoe appearance. Exercises such as cable pushdowns, straight-bar pushdowns, close-grip bench presses, and weighted dips are highly effective for targeting this area. For some individuals, reverse-grip pushdowns can also improve lateral head activation. Heavy loads and moderate repetition ranges (6–12 reps) are commonly used to stimulate growth in this head.
  
  The lateral head is also important for sports performance. In explosive actions like boxing, shot put, volleyball spiking, and football throwing, it generates power through elbow extension. A strong lateral head not only increases arm size but also improves upper-body pressing strength.

  • Medial Head

  The medial head is the deepest and often the least visible part of the triceps. It is situated beneath the lateral and long heads. It originates from the lower region of the posterior surface of the humerus and attaches to the ulna via the common triceps tendon.
  
  This muscle is considered to have a relatively high proportion of slow-twitch fibers, making it useful for endurance-oriented functions. During long-duration activities and repetitive arm movements, the medial head provides stability and sustained force production.

• Anconeus – Assists elbow extension.

This is a small muscle located at the back of the elbow. It assists when you straighten your arm (such as during push-ups or dumbbell presses). Example exercises: Triceps Pushdown, Push-ups, Close-Grip Bench Press.

• Deltoids – Help stabilize the shoulder joint during the movement.

These are the primary muscles of your shoulders. They help in lifting the arm and moving it to the front or side. Example exercises: Shoulder Press, Lateral Raise, Front Raise.

• Forearm Muscles – Maintain grip strength and wrist stability.

These are the muscles located between the wrist and the elbow. They improve grip strength. Example exercises: Wrist Curl, Reverse Wrist Curl, Farmer's Walk, Dead

• Core Muscles – Keep the body balanced and stable on the bench.

The muscles of the abdomen, lower back, and midsection collectively make up the "core." They maintain the body's balance and stability. Example exercises: Plank, Crunches, Leg Raises, Mountain Climbers. An easy way to remember

Proper Form Tips

• Keep elbows pointed forward throughout the movement.
• Lower the weight slowly and under control.
• Avoid swinging or using momentum.
• Keep wrists straight.
• Use a manageable weight for safe execution.