Skull Crushers: Benefits, Muscles Worked, and How-To (2024)

Skull crushers — no exercise has a name more intimidating than this. Sure, burpees are difficult, but their name sounds harmless enough. However, skull crushers have self-inflicted harm written all over them.

You may have heard of them, but many people don’t know what they are. They’re an excellent way to add definition and mass to the back of your arms. And with common sense and good mechanics, you can perform them safely with minimal risk of injury.

We’ll tell you everything you need to know: what skull crushers are, which muscles they work, how to perform them correctly, their benefits, and how you can modify them based on available equipment and your ability.

Let’s explore this challenging and misunderstood exercise.

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The more mundane name for skull crushers is “lying triceps extensions.” This exercise is typically performed lying on your back (supine) with a barbell or dumbbells.

Skull crushers work your triceps — the muscle on the back of your upper arm. The triceps, as the name implies, is a muscle with three heads. The long head originates above the shoulder joint on the scapula, or shoulder blade.

The medial and lateral heads originate at the back of the upper humerus and terminate at the bony point on the back of your elbow called the olecranon (1).

The function of your triceps is to extend, or straighten, your elbow as well as to help extend your shoulder, such as when you bring your arm back when walking. Your triceps is also involved in overhead throwing movements (1, 2).

The name “skull crusher” derives from the exercise mechanics of bringing the weight down to your skull from an overhead position.

If you perform the exercise incorrectly, there is some degree of risk. However, when you perform it properly, the risk is minimized, and the name “skull crusher” is nothing more than a nickname for supine triceps extensions.

Summary

Skull crushers — aka supine or lying triceps extensions — work your triceps as your elbow bends and straightens, while your shoulder muscles stabilize your shoulder joint. The name “skull crusher” derives from what can happen if you do them incorrectly.

If you’re new to this exercise, start with a low weight and work on perfecting your form. As you become familiar with the exercise and gain strength, you can slowly increase the weight you use.

Equipment used: flat bench, barbell (ideally an EZ Curl bar)

1. Sit on the bench with the barbell on your lap.
2. Grasp the barbell with a shoulder-width grip, palms facing down, while keeping your wrists straight.
3. Lie on your back as you bring the weight up to a position over your collarbone.
4. Keeping your shoulders stable, slowly bend your elbows, bringing the weight down to just past your head. Keep your elbows pointing straight ahead as you lower the weight.
5. Hold for 1–2 seconds. Then straighten your elbows, pushing the weight back to an overhead position. Keep your humerus bone fixed in space throughout the movement.
6. Perform 3 sets of 8–12 repetitions.

A 2020 study found that targeted triceps exercise helped increase bench press strength (3).

Skull crushers are one such exercise. During the movement, your triceps work in conjunction with your pectorals and anterior deltoids to push the weight up and to control it during the lowering phase.

The skull crusher is a good exercise to activate the medial head of the triceps, as compared to standing triceps extensions or other exercises in which your upper arm is at your side (4).

This can help add mass to your triceps, which is important for bodybuilders.

Thus, the skull crusher can be a good alternative to the standing overhead triceps extension exercise if you’re having pain or difficulty with overhead training.

Your triceps are involved in extending or straightening your elbow. As mentioned earlier, this is a common movement in throwing activities such as football and baseball. Therefore, skull crushers can help develop force production for those throwing muscles.

Summary

Skull crushers can help improve complex movements such as the bench press and add mass to the triceps. They’re a good alternative to standing overhead triceps exercises, and they help develop strength in muscles involved in overhead throwing movements.

Dumbbell triceps extension

This is the same exercise as the skull crusher but performed with different equipment.

It can be easier on your wrists because you can vary the angle of your forearm rotation to decrease stress. But it can provide an added challenge by requiring you to work both sides equally and maintain core stability.

As with the barbell skull crusher, start with a low weight and work on perfecting your form. Once you’re familiar with the exercise, you can slowly increase the weight.

1. Lie on your back with your arms straight and reaching toward the ceiling, holding dumbbells over your upper chest. Keep your palms either facing your feet or facing inward toward each other.
2. Keep your shoulders stable and bend your elbows, lowering the weight toward your forehead.
3. Hold for 1–2 seconds. Then straighten your elbows, pushing the weight back to an overhead position.
4. Perform 3 sets of 8–12 reps.

Resistance band skull crusher

This variation allows for greater resistance at the beginning and end phases, when your elbows are in their most extended position. It can sometimes be difficult to maintain a challenging enough resistance throughout the movement.

It’s best to do this exercise on a bench, but you can easily perform it on the floor as well. You may have to adjust your distance from the anchor point as well as the resistance band to get the proper resistance.

1. Anchor a resistance band at ground level to something very sturdy.
2. Lie on your back with your arms fully extended overhead. Grasp the resistance band and pull it so your arms are in line with your chest
3. Keep your shoulders stable and bend your elbows, lowering your hands to your forehead. Hold for 1–2 seconds.
4. Straighten your elbows, bringing your hands back over your chest.
5. Perform 3 sets of 8–12 reps.

You can perform the dumbbell and resistance band versions of the exercise with both arms, as mentioned above, or with a single arm.

Summary

You can perform variations of this exercise with dumbbells or resistance bands. You can do them with a single arm or with both arms.

The most important safety tip to consider when performing skull crushers is to move the weight with control, especially when lowering. Most injuries occur when moving the weight too fast and not controlling the position.

As you move the weight, keep your shoulder joint stable, your elbows narrow, and your wrists straight.

Keep your spine neutral as you lower the weight. Arching in your back may occur if the weight is too heavy or if your triceps are too not fully lengthening between reps. Try decreasing the weight and see if this allows you to keep your back aligned.

It’s a good idea to use a spotter when you want to increase your weight. This will ensure that you don’t actually crush your skull.

Summary

Remember to lower the weight with control. Keep your elbows in and your shoulder joints stable as you move the weight, maintaining a neutral spine.

Skull crushers are an excellent exercise to build mass and strength in your triceps. They’re also an excellent way to work on stability in your shoulders.

Remember: The name of the exercise sounds painful, but if you do it correctly, it shouldn’t cause you harm. Always perform the movement slowly and with control.

If you’ve been doing this exercise for a while, try one of the variations to add some variety or push past a plateau. Mastering the skull crusher will help you see gains across many muscles in your upper body.