Butterfly
The butterfly, usually done on a pec deck machine, is a seated chest isolation exercise where you bring your arms together in front of you in a hugging arc. It targets the chest almost by itself, without much help from the shoulders or triceps, and it suits anyone who wants a controlled, joint-friendly way to finish off a chest session.
Why it works
Your chest fibers run across the front of your rib cage, and their main job is pulling your arm across your body toward the midline, a motion called horizontal adduction. The pec deck's fixed arc lets you load exactly that motion without needing to stabilize a free weight or brace a pressing pattern, so nearly all the effort lands on the chest instead of getting shared with your shoulders and triceps the way a press would.
Set up
- Adjust the seat so the handles line up with the middle of your chest.
- Sit tall with your back flat against the pad.
- Grip the handles with a slight bend in your elbows.
How to do it
- Bring your arms together in front of your chest in a smooth, arcing hug.
- Pause briefly when your hands or forearms meet.
- Release back to the start under control, stopping before your shoulders roll forward.
- Repeat for the set without letting the weight stack slam between reps.
Form cues
- Keep a slight bend in your elbows the whole time.
- Squeeze your chest together at the point of contact instead of just letting momentum bring the pads in.
- Control the return, don't let the stack drop and yank your arms back.
- Keep your shoulder blades down and back against the pad.
Breathing: Exhale as you bring the handles together, and inhale as you return to the stretched position.
Common mistakes
Locking your elbows straight through the movement.
Fix: Keep a slight, consistent bend in your elbows so the effort stays on your chest instead of turning the exercise into a shoulder movement.
Letting your shoulders round forward at the stretched, open position.
Fix: Stop the range where your shoulder blades stay set against the pad, and don't chase extra stretch by rolling your shoulders forward.
Using too much weight and letting momentum bring the pads together.
Fix: Slow the tempo down and pick a load light enough that you control the entire arc, not just the middle of it.
How to program it
- As an isolation move, it doesn't carry the recovery demand of a compound press, so it works well twice a week placed after a pressing exercise as a chest finisher.
- Ten to fifteen reps per set is a good range, since the goal here is a controlled squeeze rather than moving maximum load.
Safety notes
- Avoid stretching past a comfortable range at the open position, since overstretching the front of the shoulder there can strain it.
- Stop if you feel pinching at the front of the shoulder rather than a chest stretch.
- Reset the seat height each session so the handles line up with your chest rather than your shoulders.
Exercise profile
- Force
- Pull
- Mechanics
- Isolation
- Category
- Strength
Frequently asked questions
How many sets and reps of butterfly should I do?
Two or three sets of ten to fifteen reps works well as a chest finisher after a heavier pressing exercise.
What muscles does the butterfly work?
Mainly the chest, through the hugging motion that draws your arms together in front of you. It isolates the chest more than a press does, with little help from the shoulders or triceps.
What's the difference between a pec deck butterfly and a cable crossover?
The pec deck moves through a fixed machine arc, which is easier to control. A cable crossover uses adjustable pulleys, giving you a wider, freer range of motion and letting you angle the pull differently.
Can I do this without a machine?
Yes. Dumbbell flyes on a bench train the same hugging arc, and bodyweight flyes are a lighter, no-equipment option.