You may have heard dumbbell exercises are better than barbell ones because they work more of your “stabilizers,” or that free weights are better than machines for the same reason. But what are stabilizer muscles? And do you really need specific exercises to train them? It turns out there are a lot of misconceptions around this term, so let me set things straight.

What are stabilizer muscles?

This is going to get fuzzy, because there isn’t really agreement on what stabilizer muscles even are. This 2014 study searched the literature for mentions of stabilizer muscles and attempted to put together a definition. Here’s what they came up with: "muscles that contribute to joint stiffness by co-contraction and show an early onset of activation in response to perturbation via either a feed-forward or a feedback control mechanism."

Okay, stabilizer muscles are muscles that, well, stabilize. Which muscles are those? That’s a harder question. A muscle might stabilize a joint while doing one type of exercise or motion, but that doesn't mean it always acts as a stabilizer. Just as an actor can play a supporting role in one movie and a starring role in another, muscles don't have to be limited to just a "stabilizer" role. Stabilizers thus aren't a type of muscle, but rather a role that a muscle may or may not play in a given context.

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Taking this back to the scientific literature: you can find plenty of research on “lumbar [lower back] stabilizers” or “trunk [core] stabilizers” or “knee stabilizers.” But these don’t turn out to be specific muscles that only stabilize joints. This study on knee stabilizers names four muscles that are part of the quadriceps and hamstring muscle groups (the big muscle groups on the front and back of the thigh, respectively). Are those stabilizers, or are they simply muscles that move the legs?

One exercise’s stabilizers may be another’s main movers

This is why I don’t worry too much about a certain exercise routine (say, one that sticks to weight machines) neglecting “stabilizing” muscles. If you do a variety of quad exercises and a variety of hamstring exercises, you’re pretty much guaranteed to hit the quad and hamstring muscles that act as knee stabilizers when you’re running and jumping.

Or to use another example: Single-leg exercises like step-ups and lunges are great for working your abductors (hip muscles) and adductors (inner thigh muscles) because those muscles work to keep your leg steady as you put weight on it. But if a person never did single leg exercises, they could still hit those muscles by doing exercises that target them as main movers, like the adductor and abductor machines.

Being stable is about coordination, not just strength

If we look again at research on knee stabilizers, scientists have a theory that it’s good for injury prevention if your body uses those stabilizer muscles while running and jumping. This isn’t just about the strength of those muscles, but also your ability to activate them when they’re needed.

So the way you keep your knees stable is not just by doing free weight exercises—although those are great—but also by doing running, jumping, pivoting, and cutting exercises. (Think soccer players running around cones and rope ladders.)

In other words, practice is important to joint stability, not just strength. If you want to be steady and stable while performing certain motions, you’ll need to train your brain to drive those muscles at the right time and in the right order.

Strength and stability are sometimes at odds

So what should you do in the gym? You may notice that strong people usually train with a mix of exercises. They might squat and bench with a barbell, but finish off their sessions with a dumbbell bench press or the leg extension machine. There is a continuum to working out, with strength on one end and stability on the other, and each of those exercises falls at a different point on that continuum.

What do you think so far?

Let’s use bench press as our example. In a barbell bench press, you need to use your legs to stabilize your torso, your torso to make a stable platform for your arms, and your arms to move the weight. Even though you’re training your pecs and triceps as the main movers, you’re getting a lot of shoulder, core, back, and leg muscles involved as stabilizers.

We can involve our stabilizers more if we were to do something like a dumbbell bench press with our back on a yoga ball. We would have to work harder to keep everything steady, but as a result, we wouldn’t be able to use nearly as much weight. We would be training stabilizers more but the main movers (chest and triceps) less.

The opposite end of that spectrum would be a chest press machine. There, you don’t have to do much stabilizing at all—just whateve

What Are Stabilizer Muscles (and Do You Really Need to Train Them)?