Reverse Pec Deck: Machine Rear Delt Fly

The reverse pec deck, also known as the machine rear delt fly or reverse fly machine, is a seated machine exercise performed by facing into the chest pad and sweeping the arms backward against the handles. It trains the posterior deltoid along with the rhomboids and middle trapezius, the muscles that pull the shoulder blades together and hold the shoulders back. Because the chest is braced and the machine controls the movement path, there is no way to cheat with the torso or lower back, which makes it far easier to feel the rear delts working than the bent-over dumbbell versions. That combination of a strict path and low skill requirement makes it one of the most reliable rear delt exercises in any gym.

Muscles Targeted

• Primary: Posterior deltoid
• Secondary: Rhomboids, middle trapezius, infraspinatus
• Tertiary: Teres minor, lower trapezius

Starting Position

Set the seat height so the handles sit at roughly shoulder height when you are seated. Move the arms of the machine to the front position for the reverse setting. Sit facing the pad with your chest pressed against it and your feet flat on the floor. Grasp the handles with a neutral grip, palms facing each other, or an overhand grip if the machine uses vertical handles. Keep a slight bend in the elbows and hold that same angle for the whole set.

Execution Steps

1. Press your chest into the pad and set your shoulder blades down, away from your ears
2. Start with the arms in front of you, handles close together and elbows softly bent
3. Sweep the arms outward and back in a wide arc, leading with the elbows rather than the hands
4. Pull until the arms are in line with your torso, squeezing the shoulder blades together
5. Pause for one second in the fully open position where the rear delts are contracted
6. Return under control to the starting position without letting the weight stack touch down
7. Repeat with the same elbow angle and the chest pinned to the pad throughout

Form Cues

• Lead with the elbows: Driving the elbows back keeps the rear delts working instead of the biceps
• Keep the elbow angle fixed: Straightening or bending the arms mid-rep turns the fly into a row
• Chest stays on the pad: Pushing off with the torso means the weight is too heavy
• Do not shrug: Keep the shoulders down so the traps do not take over
• Stop at torso level: Pulling the arms far behind the body stresses the front of the shoulder without adding contraction

Common Mistakes

• Using too much weight: Heavy loads recruit the traps and lats and turn the movement into a poor rowing motion.
• Bending the elbows through the rep: Adding elbow flexion converts a fly into a row and removes rear delt emphasis.
• Shrugging the shoulders: Letting the upper traps rise reduces posterior deltoid work.
• Letting the stack slam down: Losing tension at the start of each rep cuts the effective range.
• Sitting too low or too high: If the handles are not at shoulder height, the arc pulls the load off the rear delts.

Variations

• Single-arm reverse pec deck: Unilateral version addressing side-to-side differences
• Reverse pec deck with overhand grip: Pronated hands increasing posterior deltoid emphasis
• Cable rear delt fly: Cross-body cable version with constant tension
• Bent-over dumbbell rear lateral raise: Free-weight alternative requiring torso stability
• Face pull: Rope variation combining rear delt work with external rotation

Tips for Progression

• Increase weight gradually: Move up one plate on the stack once you can complete all reps with a one second hold
• Increase reps: Build to 15 to 20 reps, since the rear delts respond well to higher rep ranges
• Add a pause: Hold the open position two seconds to build the contraction
• Slow the return: Take three seconds to bring the arms forward for more time under tension

Training Notes

Use the reverse pec deck two or three times per week for 3 to 4 sets of 12 to 20 reps, typically at the end of a shoulder, back, or upper-body session. Rest 45 to 60 seconds between sets. The rear delts are a small muscle group that recovers quickly, so frequency and total volume matter more than load. It is a useful counterbalance for anyone who does a lot of pressing, since it directly trains the muscles that hold the shoulders back.

Frequently Asked Questions

What muscles does the reverse pec deck work?

The reverse pec deck primarily works the posterior deltoid, with the rhomboids, middle trapezius, and infraspinatus assisting. It targets the muscles that pull the shoulder blades together, which makes it a direct counterbalance to pressing-heavy training.

Is the reverse pec deck better than bent-over dumbbell flies?

The reverse pec deck is easier to learn and harder to cheat, because the chest pad blocks torso momentum and the machine fixes the path. Bent-over dumbbell flies train the same muscles with more stabilizer demand. For most lifters the machine version produces a more reliable rear delt stimulus.

How many reps should I do on the reverse pec deck?

Do 3 to 4 sets of 12 to 20 reps with a one second squeeze in the open position. The rear delts are a small, fast-recovering muscle group that responds better to frequent moderate volume than to occasional heavy sets.