Machine Chest Fly
Also called pec deck, pec deck fly, machine fly
Quick answer
Machine chest flys are a seated isolation exercise where you sweep the machine's handles together in a wide arc in front of your chest, keeping a slight, fixed bend in your elbows. They target the chest (pectoral) muscles.
Written by the GymStreak coaching team · Updated
Muscles worked
Primary
How to do Machine Chest Fly
- 1
Select a weight and adjust the height of the seat to suit you. Sit up straight and and hold the handles with a slight bend in your arms. Your arms should be parallel with your chest, adjust the height of the seat if this is not the case. Push the handles slightly to create some tension. This is your starting position.
- 2
While breathing out, push the handle togethers as much as you can.
- 3
Squeeze your chest for a second then slowly return to the starting position, inhaling while you do so.
Form cues
- Set the seat so the handles line up with your mid-chest.
- Keep a soft, fixed bend in your elbows; don't turn it into a press.
- Bring the handles together as if hugging a wide barrel.
- Keep your shoulder blades back and your upper back against the pad.
- Let the handles open slowly, stopping just before the weight stack touches down.
Breathing: Breathe out as you bring the handles together in front of you; breathe in as you let them open back out slowly.
Common Machine Chest Fly mistakes
Seat set too high or too low
Adjust the seat so your hands travel at about chest height; handles near your shoulders or belly shift work away from the chest.
Bending and straightening the elbows each rep
Lock in a slight elbow bend at the start and keep that angle so the movement comes only from the shoulders.
Rolling the shoulders forward at the finish
Keep your upper back on the pad and bring the handles together without pushing your shoulders forward off it.
Letting the arms travel too far back
Open only until you feel a good stretch across the chest with your shoulders still pinned back, rather than forcing extra range.
Letting the weight stack clang between reps
Stop each return just before the plates touch so your chest stays under tension for the whole set.
Sets and reps by goal
| Goal | Sets | Reps | Rest |
|---|---|---|---|
| Muscle growth | 3–4 | 8–15 | 60–90 s |
| Muscular endurance | 2–3 | 12–20 | 30–60 s |
Starting ranges in line with the ACSM guidance on resistance training. Pick a load you can lift with good form for every rep, and add weight or reps gradually.
Machine Chest Fly variations and alternatives
Variations
- Bent-arm pec deck
Your forearms press against vertical pads with the elbows bent at about 90 degrees; some people feel the chest more this way.
- Cable Crossover
A standing cable version that lets you change the angle of the arc.
- Incline Bench Cable Fly
An inclined fly that puts more emphasis on the upper chest.
- Dumbbell Fly
A free-weight fly on a bench, with tension highest in the stretched bottom position.
Alternatives
- Machine Chest Press
A compound machine press that also trains the triceps and front delts.
- Dumbbell Bench Press
A free-weight press for building overall chest size and strength.
- Push-Up
Works the chest anywhere, with no machine needed.
Machine Chest Fly FAQ
What muscles does the machine chest fly work?
It targets the pectoralis major, the main chest muscle, by bringing your arms across the front of your body. The front delts assist. Because your elbows stay at a fixed angle, the triceps do very little, which is what makes it an isolation exercise rather than a press.
Machine chest fly vs dumbbell fly: which is better?
Both train the same arm-sweeping action. The machine guides the path and keeps tension on the chest through most of the rep, so it's easier to learn and to take close to failure. Dumbbell flys load the chest mostly at the stretched bottom and demand more control. Choose the one you can feel working and progress steadily.
Is a pec deck the same as a machine chest fly?
Mostly, yes. Gyms use both names for a seated machine that brings your arms together in front of your chest. Some pec decks use vertical forearm pads with the elbows bent at about 90 degrees, while fly machines use handles with nearly straight arms. Both train the chest in the same way.
Should I do chest flys before or after pressing?
Most lifters do flys after their main presses, because heavy bench or machine pressing goes better with fresh muscles. Doing flys first to pre-fatigue the chest is a legitimate choice, but expect your pressing weights to drop that day.
Sources
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