How to do the chest fly

The machine chest fly, often called the pec deck, trains your chest without your triceps getting in the way. Presses stop when your arms give out; a fly lets you push your chest itself close to failure, which is why it's a staple second or third chest exercise. We'd pick the machine over the dumbbell fly for most people. The machine keeps tension on your chest all the way to the point where your hands meet, while dumbbells go almost weightless at the top, and it's much harder to overstretch a shoulder when a machine arm is guiding the path.

How to do a machine chest fly

1. Set the seat height. Sit down and check where the handles are: they should line up with the middle of your chest, so your arms are roughly parallel to the floor when you hold them. Adjust up or down until they do.
2. Set the starting position. Most pec decks have a lever or pin that moves the arms forward or back. Pick a setting where, holding the handles, your hands are level with your chest or slightly behind it, not stretched far behind your body.
3. Sit tall against the back pad. Plant your feet flat, press your back and head into the pad, and pull your shoulder blades gently back and down.
4. Grip the handles with a slight bend in your elbows. Think soft elbows, about 10 to 20 degrees of bend, and hold that angle for the whole set. On older machines with vertical pads, press through your forearms instead, with your elbows at about shoulder height.
5. Bring the handles together in a wide arc. Imagine hugging a big tree trunk. Stop when your hands meet in front of your chest, and squeeze hard for a second.
6. Open back out slowly. Take two or three seconds, and stop when you feel a strong stretch across your chest with your hands roughly in line with your body. The weight stack should stay just off its rest between reps.

When it's right, you'll feel it across your chest, most intensely in the squeeze at the front and the stretch at the back. The front of your shoulders will work a little. What you shouldn't feel is a pinch or strain deep in the front of the shoulder at the stretched end; that means the range is set too far back.

Cues for a better squeeze

"Hug the tree." Moving your arms in a curve rather than a straight push stops the movement turning into a press.

"Bring your biceps together, not your hands." If your forearms or grip seem to be doing too much, this puts the focus on your upper arms moving across your body, which is what your chest actually does.

"Chest up, shoulders down." Keeping your chest lifted toward the ceiling stops your shoulders rolling forward at the squeeze, where most people lose tension.

Common mistakes

Bending your elbows as the weight gets heavy. It starts as a fly and ends as a press, with your elbows folding in and your hands pushing forward. Your triceps join in, and the set gets easier without your chest doing more. Set your elbow angle at the start of the set and keep it. If you can't, drop the weight.

Going too deep and straining your shoulders. Setting the start position far back feels like it gives you a bigger stretch, but past the point where your hands are in line with your body, most of the extra range comes from the shoulder joint, not your chest. If the front of your shoulder aches after flys, this is the first thing to change. A strong stretch is the target; it shouldn't feel like a pull.

Using too much weight. You'll see it as short, jerky reps, the upper back peeling off the pad, and the stack slamming at the end of every rep. Flys don't reward heavy loads the way presses do. Pick a weight you can move through the full arc and pause with.

Rolling your shoulders forward at the finish. Reaching your hands past each other by hunching turns the squeeze into a shoulder shrug. Keep your back against the pad and finish when your hands meet.

Setting the seat too low or too high. Handles too high put your shoulders in an awkward raised position; too low and you're doing a strange downward press. Two seconds of adjustment fixes it, and it's worth doing every time since the last person almost certainly had a different height.

Breathing

Breathe in as your arms open, breathe out as you bring them together. Flys don't need the big brace of a heavy press, so a normal steady breath each rep is fine.

Sets, reps and weight

Do 2 to 4 sets of 10 to 15 reps after your main pressing, resting 60 to 90 seconds. Take the last set within one or two reps of failure; this is a safe lift to push hard, since there's nothing to get stuck under.

Progress by adding reps before weight. Once you can do 15 clean reps with a one-second squeeze on every set, move up one plate on the stack and work back up from 10. Pin jumps on many machines are large for an isolation lift, so if the next plate knocks you down to 6 reps, stay where you are a little longer or slow the lowering to make the same weight harder. The progressive overload guide has more on rep-first progression.

We don't give a weight table for this one. Pec deck machines vary so much in their pulleys and cams that the number on one machine tells you very little about another. Start light enough to get 15 clean reps, and compare yourself only against your own logs on the same machine.

Variations and alternatives

• Dumbbell fly: the free-weight version, done lying on a bench. Needs only dumbbells, but tension fades at the top, and it's easier to overstretch.
• Cable crossover: standing with two cables. You can change the pulley height to angle the fly up or down, and the cables keep tension right through to the squeeze.
• Single-arm machine fly: one handle at a time, sitting sideways or facing the pad. Useful for evening out a weaker side.
• Reverse pec deck: the same machine facing the other way, for your rear delts and upper back. Not a chest exercise, but a good match for all the pressing you do.

Chest fly questions

Is the chest fly machine or dumbbell fly better?

For most people, the machine. It keeps tension on your chest through the whole arc and is harder to overdo at the stretched end. Dumbbells are a fine option if you don't have a machine, or if you want to add variety.

Should I do flys before or after pressing?

After, in most cases. Presses let you load your chest heaviest, so do them fresh. Some lifters do flys first to feel their chest more during the press, but there's not much evidence that it helps, and it costs you weight on the bench.

Why do I feel the chest fly in my shoulders?

Usually because the start position is too far back, your shoulders roll forward during the squeeze, or the seat is too high. Shorten the range and sit tall against the pad. A little front delt work is normal; sharp pain isn't, and if it doesn't settle after a week or two of lighter work, get it checked.