How to Do the Skull Crusher Lying Triceps Extension

Proper Form, Variations, and Common Mistakes

skullcrusher / lying triceps extension

Verywell / Ben Goldstein

Also Known As: Skull crusher, French extensions, French presses

Targets: Triceps

Equipment Needed: Barbell or dumbbells, weight bench

Level: Intermediate

The lying triceps extension is an overhead extension performed while lying on a flat bench and using a dumbbell, two dumbbells, or a barbell. This is an isolation exercise to build the triceps muscle group in the upper arm. The skull crusher gets the name because if you use poor form you could endanger your skull. It can be used as part of an upper body strengthening or muscle-building workout.


The skull crusher is a push exercise that works the triceps brachii in isolation. It works this muscle from the elbow up to the latissimus dorsi of the back. There are variations you can do that will focus on the different heads of the muscle. This exercise is often used to fix imbalances with the triceps, for injury rehabilitation, or in bodybuilding. There are other forms of triceps extensions, such as the overhead extension, which can be an alternative. One advantage of the lying triceps extension is that it doesn't place pressure on the wrists.

Step-by-Step Instructions

Choose a flat gym bench and lie face up with legs comfortably to each side on the floor or resting on the footrest. Get into a position that provides comfort and stability.

Select a single dumbbell of suitable weight that will allow you to perform 10 to 12 extensions per set.

  1. Hold the dumbbell with both hands above your chest, straight up, and with the dumbbell shaft in a vertical position. This is the starting position. Inhale.
  2. Move the weight down toward the rear of your head by flexing your elbows while exhaling. The motion takes place in the elbows, while upper arms generally remain perpendicular to the body. Keep the upper arms from moving back and forth with the weight as this transfers some of the work to the shoulders instead of focusing it on the triceps.
  3. Continue lowering the weight behind the head until the dumbbell head is about in line with the bench top, or even a little higher if this feels unwieldy.
  4. Reverse the movement until the weight is held above the chest in the starting position again. Don't lock the elbows at the starting position; instead, stop just shy of locked position to maintain tension in your muscle.
  5. Repeat. Aim for 10 to 12 extensions for each of three sets if you don't have a defined program.

Common Mistakes

Be aware of these errors and learn to avoid them.

Grip Not Firm

Make sure you have a firm grip because the dumbbell will be traveling above the region of your head and face. You don't want to provide a literal demonstration of the skull crusher.

Lowering Weight Toward Face

Don't lower the weight toward the face or forehead; it should travel behind your head. Ensure you pass the weight over the head.

Flared Elbows

Keep the elbows in close and tight to the body. Flaring elbows is poor form, distributing the effort to other muscles.

Hitting Back of Head

Take care not to hit the back of your head when raising the dumbbell from behind the head to return to the starting position.

Lifting Too Fast or Sloppily

This exercise should be done slowly and carefully under good control.

Too Much Weight and Too Few Reps

This exercise should be done with lower weight and higher reps. It can stress the elbows and a lighter weight will help prevent that. With a lighter weight you will also be able to use better form and control.

Modifications and Variations

There are ways to do this exercise to make it more comfortable or to change how it targets your muscles.

Need a Modification?

You can place your feet on the bench with knees flexed if this suits your body shape.

You can clench the dumbbell with one hand over the other because most people will not fit two hands around a dumbbell shaft side by side.

Many people find it easiest to start doing lying triceps extensions using a barbell rather than a dumbbell. However, using a barbell (even an EZ curl bar) will produce more wrist strain than using a dumbbell.

Up for a Challenge?

You can perform this exercise on an inclined bench. This will target different areas of the triceps than when doing it lying flat.

Safety and Precautions

This exercise is known for leading to elbow pain. If you have had an elbow injury, it should be avoided. If you feel elbow pain at any time, end this exercise. You may wish to find an alternative triceps exercise that places less strain on the elbows and wrists. If using a barbell, have a spotter available in case you run into difficulty.

Try It Out

Incorporate this move and similar ones into one of these popular workouts:

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Article Sources
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