How to Do Skull Crushers for Strong, Sculpted Triceps

Skull crushers may ​sound​ like a fast-track to the emergency room, but they're actually one of the best triceps exercises for building arm strength and definition.

• ​What is a skull crusher?​ It's an arm exercise that involves lying down on your back and lowering weights toward your head by bending your elbows. You can do it with dumbbells, barbells or resistance bands.
• ​What are the main skull crusher muscles worked?​ As an isolation exercise, it targets your triceps — the muscle group in the back of your upper arms. It also works your core, forearms, grip and the stabilizing muscles in your shoulders.
• ​What's the difference between it and a lying triceps extension?​ While there's widespread "lying triceps extension vs. skull crusher" confusion, the lying triceps extension is simply the more technical term for the movement.
• ​Who can do skull crushers?​ Most people who are comfortable bringing weight overhead can do this exercise. Anyone with elbow injuries should avoid the movement until cleared by their physical therapist.

"The key thing to remember is that this is a triceps movement and not a back and shoulder movement," says Brett Durney, DPT, CPT, a physical therapist and co-founder of Fitness Lab.

Rather than employing a dumbbell pull-over motion, which shifts the work from your triceps to your lats, make sure your triceps are doing the work.

Think about pressing your upper back into the bench while you work, he suggests. As you lower the weight down, you should feel a stretch in your triceps. Then, concentrate of squeezing your triceps as you bring the weight back up over your shoulders.

You don't need a lot of resistance to work your triceps with this move. And because it's an isolation exercises, it's generally best to use light weights and higher rep counts, explains Sam Becourtney, DPT, CSCS, a physical therapist and strength coach at Bespoke Treatments in New York City.

Once doing 3 to 4 sets of 10 to 12 reps feels easy, try progressing the weight.

Also keep in mind that the equipment you use will affect how much weight you can move. Pound per pound, EZ bar and barbell triceps extensions are actually easier than skull crushers with dumbbells. That's because dumbbells load each arm separately, meaning your triceps and shoulders have to work overtime to stabilize the weights, Durney says.

To make your triceps really work for you, focus on moving as slowly as possible, explains certified strength and conditioning specialist Jake Harcoff, MS, CSCS.

This increases the amount of time your muscles are under tension and the amount of (good) muscle damage you do during your sets. "Try doing super slow reps," he says. Think: 5 seconds down, 5 seconds up.

Alternatively, you can drawing out only the eccentric — or lowering — phase of the movement. Doing so can help you build more muscle.

To truly isolate your triceps and make them take the brunt of the load, your set-up is key. Whether you're doing this move on a bench or on the floor, it's important to keep your elbows tucked — remember, your hands should never be greater than shoulder-width apart — as you lower and lift the weight.

By slowing down the movement with the last tip, you also have more control in keeping your elbows in and avoid flaring them out.

It used to be that coaches said your upper arms should stay perfectly vertical during each rep. No more.

"By incorporating a slight reach overhead — starting with the weights a bit further 'backward' over your forehead— you will really nail the long head, which is the commonly neglected part of the triceps," Becourtney says.

For a focus on the long head of your triceps (the largest segment, which we'll explain more next), try lowering the weights toward the top of your head, or even slightly behind it.

Lying triceps extensions work all three sections (aka heads) of your triceps — the medial, lateral and long head — for superior muscle and strength benefits, Becourtney says.

The medial head is the deepest of the three, with the lateral and long heads mostly covering it from view. The lateral head is the most visible, with its horseshoe shape. Meanwhile, the long head is the largest of the three.

The lying dumbbell triceps extension shines for its ability to work the long head, which many other triceps moves miss. That's because the long head connects to your shoulder, so the overhead positioning works the long head harder than elbows-at-your-sides exercises like triceps push-downs, he explains.

"Having strong triceps is fundamental for good posture," Harcoff says. Because your triceps can help pull your shoulders back, they prevent them from falling forward into a slouched position.

"This is super important for anyone who spends a lot of time at a desk throughout the day," he says.

Your triceps help you execute both pushing and pulling movements, he says. "That means that they play an important role in generating any kind of strength with the upper body."

For anyone playing a sport that involves upper-body strength, such as softball, tennis, squash or rugby, this means doing lying triceps extensions can help you win games, matches and more.

The exercise can be particularly beneficial in improving your bench press, clean, jerk and snatch, Durney says.

The triceps do more than wield raw power. They also support your shoulders and add stability to your elbows, Harcoff says.

As you strengthen your triceps, you ultimately end up supporting the health and longevity of your upper-body joints. By strengthening the muscles that supports these joints, you can significantly improve joint stability and mobility.