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Want to get rid of underarm jiggle? This exercise can help

Skull crushers isolate and tone your triceps without putting pressure on your wrists.
The skull crusher works the muscles in the back of your upper arms from the elbow to the lats.
The skull crusher works the muscles in the back of your upper arms from the elbow to the lats.TODAY Illustration / Stephanie Mansour

Skull crushers are a great move to include in your upper-body workout routine. The move targets your triceps and can also help tone your arms and improve shoulder stability.

The skull crusher, or lying tricep extension, isolates the triceps to build muscle in that area. While there are plenty of upper-body exercises that target the arms, the skull crusher is especially effective in targeting the triceps.

What do skull crushers do for the body?

The skull crusher works the muscles in the back of your upper arms from the elbow to the lats. The move can be incorporated into your workout if you’re looking to build arm strength, come back from an arm injury or just want to tone your upper body.

Stronger triceps can help make everyday activities easier, from pushing a shopping cart to pulling a heavy door open. While there are other ways to work the triceps, skull crushers are great because they don’t put any pressure on your wrists.

The common mistakes people make when doing the skull crusher

Performing skull crushers may feel unnatural if you’ve never tried the move before. I find that a lot of my clients are unsure of how to position their body and how to move the weight above their head. I also see a lot of people choosing the wrong weight for their skill level.

Ensuring that you actually target the triceps is all about form. Keep these tips in mind to avoid the common mistakes:

  • Make sure to test out different weights until you’ve found what feels right. I recommend starting with lighter weights (even as light as two pounds) and performing more reps so that you get comfortable with the movement.
  • Keep a strong grip on the weights and perform the move slowly so that you remain in control.
  • Lower the weight behind your head instead of directly toward your forehead.

How to do a modified skull crusher

Performing a skull crusher for the first time can be challenging, but there’s no need to worry. There are modifications that make it easier to perform while still providing you with the same benefits as the traditional move.

I actually recommend that everyone starts with a modification by performing the move with one dumbbell or a barbell instead of two dumbbells. This provides you with greater control since you’re only moving one weight instead of two. Lie on the floor and hold the dumbbell or barbell in both hands. (I find it easier to control with a heavier weight for this, like a five-pound dumbbell.) Lift it straight into the air above your chest. Bending at the elbows, lower the weight down behind your head, then squeeze the triceps to lift it back up toward the sky. If it's still too challenging, switch to a lighter weight.

How to perform the skull crusher correctly

Once you feel comfortable, grab two dumbbells and try the full skull crusher.

  1. Lie on the ground with your lower back pressed against the mat. Bend your knees so that your feet are flat on the ground.
  2. Hold one dumbbell in each hand and extend your arms above your chest so that the weights are parallel to each other.
  3. Keeping the upper arms still, bend at the elbows to slowly lower the weights until they reach the area behind your head.
  4. Extend your arms until they straighten out so that the weights are above your chest again.
  5. Repeat the movement, making sure to move slowly.

4 exercises that will help you perform the skull crusher

The skull crusher requires shoulder stability and strength in the triceps, so if you’re struggling, don’t worry. There are plenty of other ways to build strength in these areas so that you can perform the skull crusher with ease.

Tricep dips

Sit on a chair with your hands on either side of your hips. Bend your knees so that your feet are flat on the ground. Use your hands to lift your body off the chair and shift forward slightly so that your butt is directly in front of the seat. Lower your body toward the floor by bending your elbows to about 90 degrees. Engage your abs to maintain stability. Push through the arms to raise your body back up to the starting position. Repeat.

Overhead tricep extension

This exercise uses the same movement as the skull crusher, but instead of lying down you perform it standing up. With a dumbbell in each hand, raise your arms above your head. Bending at the elbows, lower the weights behind your head. Use your triceps to pull the weights back up toward the sky. Be sure to keep your core engaged to avoid arching in the low back.

Tricep kickbacks

Begin standing up straight with a dumbbell in each hand. Then, gently bend your knees and hinge at the hips, bringing your upper body toward the floor at a 45-degree angle. Perform a row, squeezing the shoulder blades together and pulling both elbows up toward the sky so that they are even with your rib cage. This is the starting position. From here, extend your arms straight behind you so that they’re almost parallel with the floor. Keep your upper arms glued to your sides. Bring your arms back to the starting position by bending your elbows. Repeat.


One of the most convenient, no-equipment-required moves to work the triceps is the pushup. Lie on your stomach and place your palms on the floor beside your chest. Keeping your knees on the ground, push the floor away from you to lift your weight into the air. Keep your body in a straight line. Lower yourself down and repeat.

More ways to master the move