The reverse pec deck (also called the rear delt machine fly or reverse fly machine) is one of the most beginner-friendly ways to train the often-neglected rear deltoids. You sit facing into the chest pad and push the handles backward in a wide arc, which puts the rear delts under smooth, constant tension while the machine supports your torso. Because there's no balancing or hinging to manage, you can focus entirely on feeling the target muscle work. It's a staple for building shoulder width from behind, balancing out heavy pressing, and improving posture by strengthening the muscles that pull the shoulders back.
How to do the reverse pec deck
- Adjust the seat height so the handles sit at roughly shoulder level when you're seated, then set the arm position so you start with a slight stretch across the chest rather than fully behind you.
- Sit facing the machine with your chest and torso pressed flat against the front pad, feet planted firmly on the floor for a stable base.
- Reach forward and grip the handles with a neutral grip (palms facing each other) or pronated grip (palms down), keeping a soft, slight bend in your elbows.
- Initiate the movement by driving your arms back and out in a wide horizontal arc, leading with your elbows and pinky sides, as if spreading your wings.
- Squeeze your rear delts and let the shoulder blades draw together at the back of the rep, pausing briefly at the peak contraction.
- Slowly and under control, let the handles travel forward back to the start, resisting the weight the entire way without letting it crash.
- Keep your chest glued to the pad and your neck relaxed throughout every rep.
Muscles worked
The primary muscle worked is the rear deltoids (posterior deltoid), the back portion of the shoulder responsible for horizontal shoulder abduction, pulling the upper arm backward and out to the side. The reverse pec deck isolates this head better than most pressing or rowing movements because the fixed arc keeps tension squarely on the rear delts through the whole range. The trapezius, especially the middle and lower traps, assists by retracting and stabilizing the shoulder blades at the back of each rep. The rhomboids and infraspinatus also contribute as secondary stabilizers, helping draw the scapulae together and externally rotate the shoulder.
Benefits
- Isolates the rear deltoids with constant, machine-guided tension, making it ideal for beginners still learning to feel the muscle work
- Balances out heavy chest and front-delt pressing, reducing the shoulder imbalances that lead to poor posture and impingement
- Strengthens the upper-back and scapular muscles that pull the shoulders back, supporting an upright, confident posture
- Builds rear shoulder width for a fuller, more three-dimensional shoulder look from the side and back
- Low technical demand and a supported torso make it safe and easy to progress with higher reps
Common mistakes
- Shrugging the traps: keep your shoulders down and away from your ears so the rear delts, not the upper traps, do the pulling.
- Bending and straightening the elbows: lock in a fixed slight elbow bend so the movement happens at the shoulder, not as a triceps press.
- Using too much weight and swinging: a load that forces momentum or arches you off the pad shifts work away from the rear delts; lighten it.
- Letting the weight slam back to the start: control the return so the rear delts stay under tension through the full eccentric.
- Pressing instead of sweeping: drive your arms back and out in a wide arc rather than pushing straight back like a row.
- Pulling your chest off the pad: stay glued to the pad so your back and momentum can't take over.
Form tips
- Pause for a beat at the fully open position and consciously squeeze the rear delts to maximize the contraction.
- Think about leading with your elbows or pinky fingers, not your hands, to keep tension on the rear delts.
- Use a neutral or palms-down grip; rotating the thumbs slightly down can increase rear delt recruitment.
- Keep the rep range slightly short of fully behind your body to protect the shoulder and stay in the rear delts' strongest range.
- Breathe out as you open the arms back and inhale on the controlled return.
Sets & reps
The reverse pec deck responds best to moderate-to-high reps because the rear delts are small and recover quickly. The seed programming of 3 sets of 15-20 reps with 60 seconds rest is an excellent default for most lifters. For hypertrophy and detail, stick to 3-4 sets of 12-20 reps, prioritizing a strong squeeze over heavy load. For muscular endurance or as a finisher, push to 20-25 reps. Avoid going too heavy: this is an isolation movement, so leave ego at the door and chase clean, controlled reps with a brief pause at the back. Train rear delts 2-3 times per week for best results.
Frequently asked questions
What muscle does the reverse pec deck work?
The reverse pec deck primarily targets the rear deltoids (posterior deltoid), the rear head of the shoulder. It also works the middle and lower trapezius and rhomboids, which retract the shoulder blades. This makes it a top isolation choice for building rear shoulder width and improving posture.
Is the reverse pec deck good for beginners?
Yes. It's a beginner-friendly exercise because the machine supports your torso and guides the movement along a fixed arc, so there's no balancing or hinging to manage. That lets you focus on feeling the rear delts work and learning clean form before moving to free-weight rear delt variations.
How is the reverse pec deck different from the regular pec deck?
The regular pec deck has you push the handles together in front of your body to work the chest. The reverse pec deck flips the direction: you face the pad and sweep the handles outward and back, targeting the rear delts and upper back instead of the pecs.
How heavy should I go on the reverse pec deck?
Light to moderate. The rear delts are a small muscle, so chasing heavy weight usually brings in momentum, traps, and a shortened range. Pick a load you can control for 15-20 clean reps with a brief squeeze at the back, and progress slowly once your form stays strict.
Why do my traps take over on the reverse pec deck?
Trap dominance usually comes from shrugging the shoulders up or using too much weight. Keep your shoulders pulled down away from your ears, lighten the load, and focus on driving your elbows back and out in a wide arc rather than pulling up. Leading with the pinky side also helps target the rear delts.
How often should I do the reverse pec deck?
Because the rear delts recover quickly, you can train them 2-3 times per week. Add the reverse pec deck on shoulder or upper-body days, often as an accessory after pressing work, doing 3-4 sets of 15-20 reps each session to balance out your front-delt and chest training.