The lying tricep extension, widely known as the Skull Crusher, is an isolation exercise designed to target the triceps brachii muscle, which makes up the majority of the upper arm’s mass. This movement engages all three heads of the triceps—the long, lateral, and medial heads—by focusing on elbow extension against resistance. Proper technique is necessary to maximize muscle stimulus while protecting the elbows and shoulders from strain. Understanding the setup and execution cues ensures the exercise is performed safely and effectively.
Proper Setup and Step-by-Step Execution
Lie supine on a flat bench with your feet planted firmly on the floor for stability. Use an overhand, close grip on a straight or EZ-curl bar. Extend your arms so the weight is locked out directly above your chest or slightly behind your head. Angling the upper arms back just past perpendicular to the floor helps maintain constant tension on the muscle.
The lowering phase, or eccentric portion, requires deliberate control. Without changing the angle of your upper arm relative to your torso, slowly bend only at the elbows, lowering the bar toward your forehead or just behind your head. Inhale during this descent, aiming for a slow, controlled tempo of about two to three seconds.
Initiate the pressing phase, or concentric portion, by powerfully extending your elbows. Exhale as you drive the weight back up to the starting position, focusing on contracting the triceps to achieve a full elbow lockout. Once the arms are straight, immediately begin the next controlled descent without resting the weight at the top.
Critical Form Adjustments and Injury Avoidance
Maintaining a fixed elbow position throughout the repetition is necessary for proper form. The upper arm, from shoulder to elbow, should remain stationary, pointed toward the ceiling or angled slightly backward. Allowing the elbows to drift outward shifts the stress away from the triceps and places undue pressure on the elbow joint and shoulder capsule.
The movement must be initiated and terminated by the forearm, using the elbow as the hinge. Slightly angling the upper arms back provides a greater stretch on the long head of the triceps, which is linked to greater muscle growth. Additionally, keeping the wrists straight and neutral prevents wrist strain, especially under heavy load.
A slow eccentric tempo is beneficial for both safety and muscle stimulus, as the controlled lowering phase minimizes momentum and forces the triceps to resist the weight. The bar should stop a safe distance above the forehead or slightly behind the head, establishing a consistent turnaround point. Avoid compensatory movements like arching the lower back or lifting the head from the bench, as these compromise stability and increase injury risk.
Adapting the Movement: Equipment Variations
The choice of equipment modifies the exercise’s feel and the tension profile applied to the triceps.
EZ-Curl Bar
Using an EZ-curl bar is a common adaptation because its shape allows for a semi-supinated grip. This positions the wrists in a more neutral alignment. This subtle change can significantly reduce strain on the wrist and elbow joints compared to a straight barbell, making it a preferable option for many lifters.
Dumbbells
Performing the extension with dumbbells allows each arm to move independently, which helps correct strength imbalances. Dumbbells also permit a slightly greater range of motion and a neutral grip, with palms facing each other, which can be less stressful on the elbow joint. This bilateral independence also demands greater stabilizing effort from the shoulder muscles.
Cable Machine
Utilizing a cable machine provides a different resistance curve because the tension is pulled horizontally rather than vertically by gravity. This setup ensures the triceps are under consistent tension throughout the full range of motion, including the fully extended position where free-weight tension typically decreases. The constant, smooth resistance from the cable can also be a more joint-friendly option for individuals who experience elbow discomfort.