Reverse Fly: How to Do It and Which Muscles It Works

The reverse fly works the rear deltoids and upper back muscles by raising the arms out to the sides from a bent-over or chest-supported position, and it's one of the few common exercises that directly trains the back of the shoulder

Most training programs are loaded with pressing and front-raising movements, bench press, overhead press, push-ups, that hit the front and side of the shoulder repeatedly. The reverse fly is one of the main counterbalances to that, which is why it matters more than its modest loading would suggest.

How to perform a reverse fly

Dumbbell version (bent-over)

1. Hold a light-to-moderate dumbbell in each hand and hinge forward from the hips until your torso is close to parallel with the floor, knees slightly bent.
2. Let the dumbbells hang below your shoulders with a slight bend in the elbows.
3. Raise both arms out to the sides in a wide arc, leading with the elbows, until they're roughly in line with your torso or slightly above.
4. Squeeze your shoulder blades together briefly at the top.
5. Lower with control back to the start rather than letting the weights drop.

Cable version

Cross the cables (left handle in right hand, right handle in left hand) set at roughly shoulder height, and pull both arms out and back in a reverse-fly arc. The constant tension of a cable, versus gravity-dependent resistance from a dumbbell, can make the movement feel smoother through the full range.

Machine version (reverse pec deck)

Sit facing the pad with your chest against it, grip the handles, and pull your arms back and out to the sides. The machine's fixed path makes it easier to isolate the rear delts without needing as much core or balance control as the free-weight versions.

Incline bench version

Lying chest-down on an incline bench set to roughly 30–45 degrees, with a dumbbell in each hand hanging below you, removes the lower-back demand of the bent-over version entirely since your torso is fully supported. This is a useful option for anyone who finds the bent-over hip-hinge position uncomfortable to hold for multiple sets.

What the reverse fly works

• Posterior (rear) deltoids: the primary target across all three variations.
• Rhomboids and middle trapezius: assist by retracting the shoulder blades, especially at the top of the movement.
• Rotator cuff muscles (particularly the infraspinatus and teres minor): contribute to controlling the arm through the arc and supporting shoulder joint stability.

Correct form cues

• Keep a slight, fixed bend in the elbows throughout the movement rather than locking them straight or bending them like a row. A consistent soft bend keeps tension on the rear delts rather than shifting it toward the biceps or upper back.
• Move through a controlled arc, raising the arms out and slightly back rather than straight up toward the ceiling.
• Avoid momentum. Swinging the torso or using a quick heave to throw the weights up means the rear delts are doing less of the actual work.
• Avoid shrugging the traps up toward the ears. If your shoulders rise before or during the arm raise, you're recruiting the upper trapezius instead of isolating the rear delts and mid-back.
• Use lighter weight than you'd expect. The rear delts are a relatively small muscle group, and most people need far less load here than they do for presses or rows to maintain good form.

Common mistakes

• Using too much weight, which almost always leads to using momentum or turning the movement into a row.
• Standing too upright in the bent-over dumbbell version, which reduces how directly the rear delts are loaded.
• Rushing the eccentric (lowering) phase instead of controlling the weight back down, which wastes a meaningful part of the muscle-building stimulus.
• Flaring the elbows into a full row pattern (bending them sharply and pulling toward the ribs) rather than keeping the arc wide and relatively straight.
• Letting the head drop or the neck crane forward in the bent-over version, which can creep in as the set gets harder near the end of a working set.

Breathing and setup stability

In the bent-over dumbbell version, take a breath and brace your core before starting each rep, since the hip-hinge position itself requires some trunk stability even before you add the arm movement. If your lower back fatigues before your rear delts do during a set, that's a sign the bent-over position, rather than the fly itself, is the limiting factor, and switching to the incline-bench or machine version removes that variable entirely.

Why it matters for shoulder balance

The front and side deltoids get heavy, repeated stimulation from pressing movements that most training programs already include in abundance: bench press, overhead press, incline press, push-ups. The rear delts don't get nearly the same incidental work from those lifts. Over time, that imbalance is a commonly cited contributor to rounded-forward shoulder posture and shoulder discomfort, since the muscles pulling the shoulder forward are trained far more than the ones pulling it back. Including reverse flies (or other direct rear-delt and upper-back work) a couple of times a week is a straightforward way to keep that balance in check, particularly for anyone who presses often or spends a lot of time sitting with rounded shoulders.

Sensible rep ranges and pairing

Because the load involved is light relative to most other upper-body exercises, the reverse fly tends to work well in a moderate-to-high rep range: commonly 12–20 reps for 2–4 sets, prioritizing a controlled tempo and full shoulder-blade squeeze over chasing heavier weight. It pairs naturally with pressing work: many people add a set or two of reverse flies, face pulls, or band pull-aparts after their main chest or shoulder press for the session, specifically to address the front-to-back imbalance discussed above. If you're logging your training, it's worth tracking rear-delt work separately from pressing volume so it doesn't quietly get skipped when a session runs short on time. It's one of the easiest accessory movements to drop first, and often the one that matters most for long-term shoulder health.

Signs you need more rear-delt work

A few practical indicators suggest the rear delts and upper back could use more direct attention: shoulders that round forward when standing relaxed, noticeably more strength and muscle development on the front of the shoulder compared to the back, or general shoulder fatigue and discomfort after sessions heavy on pressing. None of these are a precise diagnosis on their own, but together they're a reasonable prompt to add a dedicated rear-delt movement like the reverse fly rather than relying on the small amount of incidental rear-delt work that rowing exercises provide.

It's worth being realistic about what the reverse fly can and can't fix on its own: it strengthens and builds the muscles that pull the shoulder blade back, but posture habits built up over years of sitting and desk work usually need ongoing attention to movement and sitting posture throughout the day as well, not just a few sets of an exercise once or twice a week.