Single-Arm Skull Crusher — Muscles Worked, How-To, Benefits

Fully developed triceps add size and shape to your upper arms. The impressive horseshoe shape of the muscle looks great in a t-shirt and counterbalances a flexed biceps.

One of the most popular triceps exercises is the skull crusher, also known as the lying triceps extension. In this article, we go over the unilateral version of the conventional exercise — the single-arm skull crusher. You’ll learn how to do the single-arm skull crusher with the perfect form, the benefits, and the variations and alternatives of the exercise.

In This Exercise:

Target Muscle Group: Triceps
Type: Hypertrophy, strength
Mechanics: Isolation
Equipment: Dumbbell
Difficulty: Beginner to Advanced

Triceps Anatomy

The triceps is a three-headed muscle at the back of your humerus or upper arm bone. The three heads are the lateral, medial, and long heads.

Although the three heads have different points of origin, they have the same insertion point, just below the elbow. While the lateral and medial heads originate on the back of the humerus bone, the long head originates on the scapula, a little below the shoulder socket.

The primary function of the triceps is elbow extension or the straightening of the elbow.

Muscles Worked

The single-arm skull rusher targets the triceps as it moves the triceps through its full range of motion. The elbow extension isolates the tricep so that it is the only muscle involved in the exercise. All three heads of the muscle are engaged in the exercise.

How to Perform the Single-Arm Skull Crusher

Here is how to perform the exercise with the correct form:

Lie on a flat bench with your feet firmly planted on the floor. Hold a dumbbell in your right hand with a neutral (hammer) grip.
Extend the arm straight so it is perpendicular to the floor.
Your elbow should be locked at the starting position.
While keeping your elbow pinned in place, lower the dumbbell down to the side of your head, alongside your ear. Resist the weight as it comes down.
In the bottom position, your elbow should be bent at 90-degrees.
Push through the tricep muscle to return to the start position.
Pause and contract your triceps at the top.
Do not lock out the elbow joint between reps.

Training Notes:

As the exercise gets harder, many people tend to flare out their elbows. To prevent this, you can use your free hand to brace the elbow of the working arm.
You do not have to go super heavy weight on this exercise. Focus on isolating the triceps muscle and moving the weight in a straight line.

Common Mistakes

Below are a couple of mistakes many lifters commit while performing the exercise:

1. Elbows Drifting Out

When the elbows are allowed to flare out away from the head, the emphasis is taken off the triceps and put on the shoulders. This usually happens because the weight is too heavy. With the single-arm skull crusher, you can use your free hand to brace your working-arm elbow.

2. Using Momentum

Many lifters cheat on the exercise by jerking their arm forward and backward to make the movement easier. However, it takes the emphasis off your triceps and puts it on your deltoids.

Single-Arm Skull Crusher Benefits

Advantages of the single-arm skull crusher include:

The single-arm skull crusher is a unilateral exercise as it allows you to train each arm separately, helping correct muscle and strength imbalances. When you use a barbell, the stronger side takes over, causing the bar to travel up at an angle. However, when you train each arm separately with dumbbells, the muscle must carry its own load.
The single-arm skull crusher allows you to use dumbbells. As a result, you can grab the weight with a neutral, or hammer, grip. This position is more wrist-friendly and helps prevent your elbows from flaring out.
Many people find it easier to develop a mind-muscle connection when they train one muscle at a time. They are able to better concentrate on flexing, contracting, and stretching the muscle.
This exercise can be done with just a single dumbbell, making it better suited to home training situations where people have limited training gear.
The starting position of the single-arm skull crusher, with your arm directly up above your chest, puts the tricep in a pre-stretch position. This does not happen when you start a triceps exercise with your arms at your side, such as when you are doing triceps press-downs.

Single-Arm Skull Crusher Drawbacks

Performing the single-arm skull crushers entails the following disadvantages:

The single-arm skull crusher takes twice as long to complete compared to the conventional double-arm version.
People with shoulder mobility problems may experience pain when performing this exercise.

3 Single-Arm Skull Crusher Variations

Here are a few single-arm skull crusher variations worth trying:

1. Kettlebell Single-Arm Skull Crusher

The kettlebell single-arm skull crusher provides a unique type of resistance for the exercise. The weight is positioned more directly under your hand, making it harder to push the weight up from the bottom position.

Lie on a flat bench with your feet planted on the floor while holding a kettlebell in your right hand with a pronated grip.
Extend your arm straight so that the kettlebell is above your mid-chest.
Bend at the elbow to bring the kettlebell down to your forehead.
Push through the tricep muscle to return to the start position.

2. Cable Single-Arm Skull Crusher

The cable single-arm skull crusher provides the advantage of continuous tension so that your muscles are working constantly from the start of your first rep until the completion of your last rep.

Position a flat bench about two feet in front of a cable pulley machine. Adjust the cable pulley to its lowest setting. Lie on the bench with your feet firmly planted on the floor.
Grab the cable in your right hand with a palm forward grip and extend your arm directly above your mid-chest.
Bend at the elbow to bring the cable down to your forehead.
Push through the triceps muscle to return to the start position.

3. Resistance Band Single-Arm Skull Crusher

The resistance band single-arm skull crusher is similar to the cable version of the exercise. To make the exercise harder, you move the bench further away from the anchor point. The resistance on the banded skull crusher varies throughout the exercise. It is harder at the arm extended position and easier at the arm bent position.

Secure a resistance band around the base of a sturdy upright. Place a bench around three feet in front of the upright. Lie on the bench with your feet firmly planted on the floor.
Grab the handle of the resistance band in your right hand with a palm forward grip and extend your arm directly up above your mid-chest.
Bend at the elbow to bring the band down to your forehead.
Push through the tricep muscle to return to the start position.

FAQs

Do Skull crushers build mass?

Yes, the skull crusher is a very good exercise to build mass in your triceps. It also helps in building strength.

Are single-arm skull crushers better than doing them with both hands?

The single-arm skull crusher allows you to work each arm individually, helping overcome strength and muscle size imbalances. You can also use your non-working hand to brace your elbow. Nonetheless, it will take twice as long to complete your workout when you do the single-arm version.

More Skull Crusher Exercises:

Wrapping Up

The single-arm skull crusher is an incredibly effective exercise to ensure balanced triceps development. If you have noticed a strength or muscular development imbalance between your left and right triceps, this exercise can help you correct the problem.

The single-arm skull crusher can also help you improve your mind-muscle connection. So, if your triceps development needs prioritization, this may be a good exercise to include in your workout.