The rear delt fly is the classic isolation move for the back of the shoulders — the counterbalance to all the pressing most people do. Here's how to do it with good form, the muscles it works, the mistakes to avoid, and how to program it.
The rear delt fly is an isolation exercise that primarily works the rear (posterior) deltoids, with help from the upper back — the rhomboids and middle traps. You hinge forward (or sit at a reverse pec deck) and raise the weights out to the sides in a wide arc, squeezing the shoulder blades at the top. It's a light, high-rep movement that builds the often-neglected back of the shoulder, which supports balanced, healthy shoulders and better posture as a counter to heavy pressing.
The rear delt fly is an isolation move, so it keeps tension focused on the back of the shoulder. The rear delts do the work, assisted by the upper-back muscles that draw the shoulder blades together.
| Role | Muscles | What they do in the lift |
|---|---|---|
| Primary mover | Posterior deltoid | Raises the arm out and back (horizontal abduction) |
| Assisting | Rhomboids, middle traps | Draw the shoulder blades together at the top |
| Assisting | Infraspinatus, teres minor | Help rotate and stabilize the shoulder joint |
| Stabilizers | Erector spinae, core | Hold the hinged torso position steady |
Step-by-step form for the bent-over dumbbell rear delt fly. If you're new, start very light — this is a movement you feel, not one you muscle.
If you want to train the rear delts and upper back with a different emphasis or equipment, these are the common swaps:
The rear delt fly is an accessory that fits on shoulder, pull or upper-body days. General starting points:
| Goal | Sets × reps | Notes |
|---|---|---|
| Muscle size | 3–4 × 12–20 | Light load, strict control, squeeze the rear delts at the top |
| Shoulder health | 2–3 × 15–25 | Very light, high reps as postural balance work — quality over load |
| Frequency | 2–3× / week | Rear delts recover quickly, so they tolerate frequent light work |
The rear delt fly pairs well with the face pull and the lateral raise to round out the shoulders. To keep your shoulders resilient under all that pressing, read up on shoulder health.
Log every rear delt fly set — weight and reps — in LiftHero, and it charts your progressive overload and flags personal records so you can see this often-neglected muscle actually getting stronger over time. You can superset flies with pressing, add rest-timer holds, and save the whole shoulder session as a routine. LiftHero records what you log; it doesn't diagnose your form.
It mainly isolates the posterior (rear) deltoids, with help from the upper-back muscles — the rhomboids and middle traps. It's a horizontal pulling motion that balances all the pressing most people do.
The rear delts and upper back often lag behind the chest and front delts because pressing dominates most programs. Training them directly supports balanced shoulders, better posture and a fuller-looking shoulder from the side and back.
No. The rear delts respond best to lighter weight and higher reps with strict control. Going too heavy forces you to swing and turns the movement into a row or a shrug, which takes tension off the target.
Both train the same muscles. The reverse pec deck (or a cable) keeps constant tension and is easy to set up strictly; bent-over dumbbell flies are more accessible and challenge stability. Many lifters rotate between them.
Both target the rear delts and upper back. The fly is a wide arc with straighter arms that isolates the rear delts; the face pull pulls toward the face with the elbows high and involves more upper-back and rotator-cuff work.
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This guide is educational and not medical advice. Consult a qualified coach or medical professional before starting or changing a training program, especially if you're new to lifting or returning from injury.
By Meitar Lazimi, founder of LiftHero · Last updated July 9, 2026.