What muscles does the dumbbell fly work?

The chest does the work. Bringing the arm across the front of the body is the chest job, and a fly is that movement with nothing else attached. The front of the shoulder assists. The triceps cannot contribute, because the elbow angle never changes.

Is the dumbbell fly better than the bench press for the chest?

No. When they were compared directly, the bench press produced higher chest activity. The fly earns its place differently: it loads the chest at a longer stretch than any press reaches, and it gives the triceps no way to help.

How low should you go on a dumbbell fly?

To the point where you feel a stretch across the chest and the shoulder still feels settled. Lowering until the arms will not go further adds range at the shoulder joint rather than load on the chest.

Why do flies feel so much lighter than a press?

They should not feel lighter, they should feel heavy at the bottom and light at the top. A dumbbell pulls straight down, so the chest works hardest when your arm is stretched out sideways and barely at all once the dumbbells are over your shoulders. Expect a much smaller dumbbell here than the one you press with.

Should your elbows be straight or bent on a fly?

Softly bent and then locked at that angle for the entire set. Straight arms put more strain on the elbow than most people want, and an angle that changes during the rep means you are pressing, not flying.

Do flies build inner chest?

No, and the thing people point at when they say it is the edge of the muscle where it meets the breastbone. That edge is where your chest is attached, and attachment points do not move. What a fly does do is load the whole muscle at a longer stretch than a press.

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Dumbbell · beginner · chest

Dumbbell flys flat

Also called Chest fly, Dumbbell flye, Flat bench fly, Pec fly, Dumbbell fly.

The short answer

The flat dumbbell fly opens the arms out to the sides and brings them back together over your chest with the elbow angle held fixed. Your chest does the work almost alone, because bringing the arm across the body is the one job the chest has. The front of your shoulder assists. Since the elbows never bend and straighten, the triceps cannot help, which is what separates this from a press.

How to do it

Step oneLie flat on a bench holding a dumbbell in each hand, arms extended directly above your chest.
Step twoWith a slight bend in your elbows, lower the dumbbells out to the sides in a wide arc.
Step threeContinue lowering until you feel a deep stretch across your chest.
Step fourReverse the motion and bring the dumbbells back up in the same arcing path until they meet above your chest.

What usually goes wrong

Each starts with what you would notice.

Your triceps and shoulders are working, and the movement feels like a wide bench press.

WhyThe elbows are bending on the way down and straightening on the way up. That is a press with a wide arm path, and the triceps and front delt are now sharing the load the chest was supposed to carry.

FixSet a soft bend in the elbow before the first rep and freeze it there. The angle at your elbow should be identical at the top, the bottom and everywhere between.

The dumbbells go straight up and straight down.

WhyYou are pressing. A fly travels in an arc out to the sides, not a line up from your chest.

FixWatch the dumbbells, not the ceiling. They should sweep out sideways and back in, tracing a wide arc as if you were closing your arms around something large.

You cannot keep the elbow angle fixed no matter how hard you try.

WhyThe dumbbells are too heavy. Bending the elbow is how your body shortens the lever to make a load it cannot handle possible.

FixDrop the weight, by a lot if necessary. A fly holds the arm out at nearly full length, so the usable dumbbell here is far smaller than the one you press with. That is the exercise, not a failing.

The front of your shoulder feels stretched to its limit at the bottom.

WhyThe arms are going as low as they physically can rather than as low as the chest is loaded.

FixStop where you feel the chest stretch and the shoulder still feels settled. Going lower adds range at the joint, not at the muscle. If something hurts and keeps hurting, that is a question for a physiotherapist.

Your shoulders roll up off the bench as the dumbbells come down.

WhyWith the arms out wide the load pulls the shoulders forward, and nothing stops it if the shoulder blades have not been set.

FixBefore the first rep, pull the shoulder blades down and together so your chest is the highest point. Hold that for the whole set and reset between sets rather than mid-rep.

Fly or bench press

The fly is usually sold as the movement that isolates the chest and therefore works it hardest. When 17 resistance-trained men did both, the barbell bench press produced higher chest activity than the dumbbell fly, not lower. So the standard argument for the fly does not survive contact with the measurement.

What does survive is the position. A press stops when the dumbbells reach your chest. A fly keeps opening past that, so the chest is loaded at a length a press never gets near. And because the elbow angle never changes, the triceps has nothing to contribute, which a press cannot say.

The sensible reading is that the press is the movement to load and the fly is the one that reaches a position the press cannot. Not a replacement, and not the better chest exercise.

Why it gets easy at the top

A dumbbell pulls straight down and nothing else. How hard your chest has to work at any point in the rep depends on how far the dumbbell is from being directly above your shoulder.

At the bottom of a fly your arm is stretched out sideways, so the dumbbell is a long way out from the joint and the chest is working at its hardest. As the arms close, the dumbbell moves toward a point straight above the shoulder, and by the top there is almost nothing left to hold.

That is why squeezing at the top of a fly does very little. It is not a criticism of the movement, it just tells you where the useful part of the rep is. Control the lowering, own the stretched position, and do not waste effort chasing a contraction the load has already let go of.

Width, definition and the inner chest

The claims stacked on this movement are unusually loose. Chest width, chest definition, the inner chest. It is worth taking those apart, because they are the reason people keep flying instead of pressing.

Width is your rib cage and your collarbones, and no exercise changes those. Definition is a body composition question, not something a movement pattern delivers. And there is no inner chest to train: the chest is one muscle with two heads, both running from the middle of your body out to the arm, and no arm path selects a strip down the middle of it.

Take away the promises and there is still a reason to do this. It loads the chest in a stretched position nothing else with a pair of dumbbells reaches, and it does it with no way for the triceps to take over. That is a specific job and worth a couple of sets. It is not the movement that builds a chest on its own.

What it is for

Dumbbell flat flys are an isolation chest exercise targeting the pectoral muscles. The wide arcing motion stretches and contracts the chest through a large range of motion, making it effective for developing chest width and muscle definition.

Questions people ask

What muscles does the dumbbell fly work?: The chest does the work. Bringing the arm across the front of the body is the chest job, and a fly is that movement with nothing else attached. The front of the shoulder assists. The triceps cannot contribute, because the elbow angle never changes.
Is the dumbbell fly better than the bench press for the chest?: No. When they were compared directly, the bench press produced higher chest activity. The fly earns its place differently: it loads the chest at a longer stretch than any press reaches, and it gives the triceps no way to help.
How low should you go on a dumbbell fly?: To the point where you feel a stretch across the chest and the shoulder still feels settled. Lowering until the arms will not go further adds range at the shoulder joint rather than load on the chest.
Why do flies feel so much lighter than a press?: They should not feel lighter, they should feel heavy at the bottom and light at the top. A dumbbell pulls straight down, so the chest works hardest when your arm is stretched out sideways and barely at all once the dumbbells are over your shoulders. Expect a much smaller dumbbell here than the one you press with.
Should your elbows be straight or bent on a fly?: Softly bent and then locked at that angle for the entire set. Straight arms put more strain on the elbow than most people want, and an angle that changes during the rep means you are pressing, not flying.
Do flies build inner chest?: No, and the thing people point at when they say it is the edge of the muscle where it meets the breastbone. That edge is where your chest is attached, and attachment points do not move. What a fly does do is load the whole muscle at a longer stretch than a press.