Most people think they have a "back day." They don't. They have a "lat and trap day" that completely ignores the tiny, stubborn muscles responsible for making you look three-dimensional. If you look in the mirror and your shoulders seem to roll forward like a caveman, or if your side profile looks strangely flat despite a heavy bench press, you’re missing the bent over rear delt fly.
It’s a fickle move. Honestly, it’s one of the easiest exercises to mess up because the ego takes over. You see guys in the gym grabbing 50-pound dumbbells and flailing their arms like they’re trying to take flight. That’s not a rear delt fly. That’s a recipe for a trap strain and zero shoulder growth. To actually hit the posterior deltoid, you have to stop thinking about moving heavy weight and start thinking about precision.
Why the Bent Over Rear Delt Fly Is Non-Negotiable
The posterior deltoid is small. It’s tucked away behind the beefy lateral head of your shoulder, and its primary job is horizontal abduction—pulling your arm back and away from your chest.
Why do we care? Posture.
Modern life is a disaster for shoulders. We spend ten hours a day hunched over MacBooks or scrolling through TikTok, which shortens the pecs and overstretches the rear delts. This creates that "rounded" look. The bent over rear delt fly acts as the structural counter-balance. It pulls the humerus back into the socket. Dr. Mike Israetel from Renaissance Periodization often points out that while heavy rows hit the rear delts to some degree, they usually get overpowered by the lats and rhomboids. You need isolation.
If you want that "cannonball" shoulder look, you can't just spam side raises. The rear delt provides the "back" of the shoulder ball. Without it, your physique looks unfinished. It’s the difference between a flat 2D image and a 3D sculpture.
The Form: It's Kind Of Counterintuitive
Forget everything you know about "squeezing your shoulder blades together." Seriously.
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When you perform a bent over rear delt fly, most people make the mistake of retracting their scapula. If you pinch your shoulder blades at the top, you’ve just turned a shoulder exercise into a middle-trap exercise. The traps are much stronger than the rear delts. If they can take over, they will.
The Setup
- Grab light dumbbells. No, lighter than that. Most advanced lifters rarely go over 20 or 25 pounds for high-quality reps.
- Hinge at the hips until your torso is nearly parallel to the floor. If you stand too upright, you're just doing a weird lateral raise.
- Let the weights hang. Now—and this is the "secret"—protract your shoulders slightly. Feel like you’re reaching for the floor.
- Keep a slight bend in the elbows.
The Execution
Instead of pulling the weights "up," think about throwing them "out" to the side walls. Imagine there’s a string attached to your elbows pulling them toward the corners of the room. You want to keep your shoulder blades relatively still. By keeping the scapula spread wide, you force the posterior deltoid to do the heavy lifting.
Stop the movement once your arms are level with your torso. Going higher usually just kicks in the traps again. You’ll feel a sharp, localized burn right on the back of the shoulder. If you feel it in your neck or between your shoulder blades, you’re trying too hard to "squeeze."
Variations That Actually Work
Dumbbells are the classic choice, but they aren't always the best. Gravity is a bit of a jerk with dumbbells; there’s zero tension at the bottom of the move and peak tension at the top.
Cables solve this.
By using a cable crossover machine, you can cross the wires so the resistance is pulling your arms inward at the start. This provides a stretch on the rear delt that dumbbells just can't match.
Then there’s the chest-supported fly. This is probably my favorite for people who have lower back issues or tend to "cheat" by swinging their hips. Lay face down on an incline bench set to about 30 degrees. This removes all momentum. You can’t use your legs or your lower back to move the weight. It’s pure, isolated misery for your shoulders.
Coach Joe Bennett (the "Hypertrophy Coach") often talks about the importance of the line of pull. If you rotate your pinkies up toward the ceiling as you fly, you might find it hits the muscle differently. Others prefer a neutral grip. Try both. Your anatomy is unique.
Common Blunders You're Probably Making
We need to talk about momentum. Most people use a "bounce" at the bottom of the rep. They use the stretch reflex to slingshot the weight up.
Stop doing that.
The bent over rear delt fly is most effective when you use a dead stop or a very controlled tempo. Try a two-second hold at the top of the movement. If you can't hold it there, the weight is too heavy. It's a humbling realization, but your shoulders will thank you in six months.
Another issue is head position. Don’t look up at the mirror. It puts your cervical spine in a funky position. Keep your neck neutral—look at a spot on the floor about three feet in front of you.
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Programming for Growth
How often should you do these?
Rear delts can handle a lot of volume. They are primarily slow-twitch fibers, meaning they recover quickly and respond well to higher reps. Think 12 to 20 reps per set.
- Frequency: 2–3 times per week.
- Placement: Put them at the end of your back or shoulder workout.
- Intensity: Go to technical failure. Since the weight is light, the risk of injury is low, so you can really push the metabolic stress (the "burn").
Some lifters, like the late John Meadows, swore by "swing" sets. This involves using heavier dumbbells and doing partial reps at the bottom of the movement for high volume (30+ reps). It’s an advanced technique, but it’s incredible for bringing up lagging delts.
Actionable Steps for Your Next Workout
Don't just read this and go back to your 3 sets of 10. Change the way you approach the movement.
Start your next session with a "primer" set. Take 5-pound plates and do 20 slow, controlled reps of the bent over rear delt fly just to establish the mind-muscle connection. Focus on keeping the shoulder blades "wide" and pushed away from each other.
Once you feel that specific spot on the back of your shoulder firing, move to your working sets.
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If you’ve been plateauing in your overhead press or feeling "tight" in the front of your chest, focus on these for four weeks. Consistency here fixes the "rounded shoulder" look better than any foam rolling ever will.
- Select a weight that is 50% of what you think you should use.
- Perform 3 sets of 15-20 reps on a chest-supported bench.
- Hold the peak contraction for a full second.
- Record your sets from the side to ensure your torso isn't rising up as you fatigue.
The goal isn't to be the strongest person doing flies; it's to have the most developed shoulders in the room. Put the ego away, tuck the chin, and start flying.