When you’re thinking of moves that work your legs, squats, lunges, and deadlifts are probably front and center. But the wall sit exercise is actually a great option to add to your workout routine.

So what exactly is the wall sit? The wall sit exercise is exactly as it sounds: Imagine sitting on a box in front of a wall with your back flat against said wall. Now, think about taking the box away. The muscles in your legs need to fire to keep your body steady as you hold that seated position—that’s a wall sit.

Wall sits are great lower-body exercises for beginners, people coming back from injury, or exercisers looking for a greater challenge. In fact, one of the great things about the wall sit is that it’s super customizable to a whole bunch of fitness levels.

Interested in giving the wall sit exercise a try? Before we demonstrate how to wall sit, read on for some background on the exercise, as well as some tips on how to put it into practice in your exercise routine.

What is the wall sit exercise?

The wall sit exercise is a lower-body strengthening exercise that works your muscles through isometric contractions, or by holding a position without moving, certified strength and conditioning coach Evan Williams, CSCS, CPT, founder of E2G Performance, tells SELF.

Here’s a quick refresher: Your muscles perform three types of actions: concentric, eccentric, and isometric. In the context of a squat exercise, when you’re lowering your butt toward the floor, your muscles are lengthening in the eccentric phase. When you’re pushing back up, your muscles are shortening in the concentric phase. In between the two? When you pause at the bottom of the squat—when you’re staying still, but your muscles are still firing to maintain tension—that’s the isometric phase. (In addition to the wall sit, other classic isometric exercises you might know include any type of plank and the glute bridge hold.)

The wall sit basically takes the isometric portion of the squat and blows it out into its own, leg-quaking move.

What muscles does the wall sit exercise work?

The wall sit exercise is a lower-body move that works your quadriceps, or the muscles in the front of your upper thighs, Williams says. You also get slight activation of your lower leg muscles, like your calves, as well as your core and glutes, but the wall sit primarily targets your quads.

“When you’re in that seated position—that in-between phase of the eccentric and concentric contractions—you’re really activating your quads by pushing through the ground, and not allowing yourself to fall or rise from your position,” Williams says. “You’re fighting gravity to maintain that seated position. We call that time under tension.”

What are the benefits of the wall sit exercise?

The wall sit exercise is great for building strength in your quads, which help you extend your knee and flex your hip—meaning your quads help you do everything from walking to running and from getting up from a chair to climbing up stairs. Your quads also play a role in knee stability, and strong quads have been shown to help reduce the risk of knee pain.