MariposasHow to Do the Rear Delt Fly
By Zachary, builder of Mariposas · Reviewed against published exercise-science sources (references)
· Last updated June 2026
The rear delt fly sits in an odd category: most people skip it, and most people also wonder why their shoulders look flat from the side and why their upper back rounds forward. The rear deltoid is almost impossible to load meaningfully with compound pressing or rowing movements, because those exercises let the larger muscles of the upper back and chest dominate. The dumbbell rear delt fly isolates the posterior head of the deltoid and the surrounding upper back musculature by removing that compensation option entirely, putting the load exactly where it needs to go. That specificity is what makes it earn its place in a program even when a lifter is already doing rows and face pulls. Track every set and session for free in the Mariposas app.
How to do it
- Set up by hinging at the hips until your torso is roughly parallel to the floor, or close to it, with a dumbbell in each hand hanging straight down from your shoulders and a soft bend in your knees.
- Before the rep begins, retract your shoulder blades just slightly, not aggressively, so you are not starting from a position where your rear delts are already slack.
- Initiate the movement by driving your elbows outward and upward, thinking of the elbow as the lead point rather than the hand, which helps keep the rear delt as the prime mover.
- Raise the dumbbells in a wide arc until your upper arms are roughly level with your torso, stopping when the weights are approximately in line with your ears, not above them.
- At the top of the rep, briefly pause and feel the squeeze between your rear delts and upper back before reversing the motion.
- Lower the dumbbells under control along the same arc, taking about twice as long on the way down as you did on the way up, resisting gravity rather than dropping the weight.
- Reset your position between reps if needed, especially if your torso drifted upright, because losing the hinge removes most of the tension from the rear delt.
- Complete all reps, then stand slowly to avoid a head rush from the prolonged hinge position.
Form cues
- Elbows lead, not hands.
- Stay hinged. If you stand up, the set is over.
- Pinch at the top for one full second.
- Think wide arc, not straight back.
- Lighter than you think. Own the range.
Common mistakes
- Using too much weight and turning the movement into a shrug: when the dumbbells are too heavy, the upper traps take over and the rear delts get almost no stimulus, so dropping the weight by 30 to 40 percent and slowing the eccentric is usually the fix.
- Letting the torso rise during the set: as fatigue builds, many lifters unconsciously stand more upright, which shifts the load away from the rear delt entirely and turns the movement into something closer to a lateral raise, so anchoring your gaze at a fixed spot on the floor helps maintain position.
- Pulling the elbows behind the body rather than out to the side: this common error recruits the upper back more broadly but shortens the effective range of motion for the rear delt specifically, and thinking of drawing a wide half-circle with each elbow corrects the path.
- Rushing the eccentric and dropping the weight: the rear delt is a relatively small muscle that responds well to time under tension, and a fast lowering phase throws away roughly half the stimulus of each rep.
- Bending the elbows too much to make the weight feel lighter: a slight bend in the elbow is fine and actually reduces joint stress, but when the arms are deeply bent the lever arm shortens significantly and the rear delt does far less work, so maintaining a consistent, gentle bend throughout the rep matters.
Why do the Rear Delt Fly?
- The rear delt is one of the few muscles in the shoulder complex that pulling and pressing movements consistently undertrain, and the dumbbell fly addresses that gap directly, which tends to contribute to more balanced shoulder development over time.
- Strong rear delts help oppose the forward pull of the pectorals and anterior deltoid, and many lifters find that consistent rear delt work contributes to improved posture and a more upright resting shoulder position.
- The upper back musculature trained here plays a role in scapular stability during overhead pressing, meaning rear delt fly work can show up as improved control in unrelated movements.
- Because it is an isolation exercise with a modest range of motion, the rear delt fly is accessible to lifters who cannot yet load heavier compound row variations heavily, making it a useful supplemental tool across a wide range of training ages.
Rear Delt Fly variations
- Cable Rear Delt Fly (bent-over)
- The cable version maintains constant tension through the full arc rather than dropping off at the bottom like dumbbells do, making it a useful progression for lifters who have already dialed in the movement pattern and want a different stimulus.
- Seated Rear Delt Fly (chest-on-thigh)
- Sitting and resting the chest on the thighs removes the need to stabilize the hinge position, which makes this a practical regression for beginners who struggle to maintain the bent-over position without their torso drifting.
- Single-Arm Dumbbell Rear Delt Fly
- Working one arm at a time lets a lifter focus on the mind-muscle connection and identify side-to-side asymmetries, and it is commonly used by people who have noticed that one rear delt lags visually or feels less involved during the bilateral version.
- Rear Delt Fly on Incline Bench (prone)
- Lying face-down on an incline bench locks the torso angle completely and eliminates any cheating through hip extension, making it a stricter environment that is particularly useful for intermediate lifters trying to break through a plateau caused by form drift.
How to program it
The rear delt fly almost always appears later in a session, after compound pressing or pulling work, because it functions as an accessory or finishing movement rather than a primary strength exercise. Many lifters use it in the 12 to 20 rep range with lighter loads, prioritizing the quality of contraction over progressive overload in the traditional sense, though some run it in moderate ranges around 8 to 12 reps with slightly heavier weights. It fits naturally on push days, pull days, or upper body days depending on how a program is organized. Volume tends to accumulate across two to four sets per session, often appearing two to three times per week in programs that emphasize shoulder development or address rear delt imbalances.
Rear Delt Fly alternatives
FAQ
- Why can't I feel my rear delts during the fly, only my traps?
- This almost always comes down to weight being too heavy combined with an elbow path that drifts backward instead of outward. Drop the weight significantly, slow the movement way down, and focus on driving the elbows out to the sides in a wide arc. Many lifters also find it helpful to hold the top position for two to three seconds per rep until the mind-muscle connection improves.
- How is the rear delt fly different from a face pull?
- Both train the rear delt, but they involve different movement patterns. The face pull typically involves external rotation and tends to recruit the upper back more broadly. The rear delt fly is a pure horizontal abduction movement with very little rotation, making it more specific to the posterior deltoid head itself. Many programs include both.
- Should my arms be completely straight during a rear delt fly?
- A small, consistent bend in the elbow, around 10 to 20 degrees, is the standard approach. It reduces stress on the elbow joint and is generally more comfortable over high rep ranges. What you want to avoid is letting that bend increase as the set gets harder, because that effectively shortens the lever and reduces rear delt demand.
- How heavy should I go on the rear delt fly?
- Most experienced lifters use dumbbells that feel almost embarrassingly light compared to what they use for other shoulder work. The rear delt is a small muscle, and the leveraged position of the fly makes even modest loads challenging when the form is strict. Starting lighter than you think you need to and earning the weight over several sessions is the consistent advice in this movement.
- Can I do rear delt flies standing upright instead of bent over?
- If you stand fully upright, the exercise changes substantially and you lose most of the rear delt emphasis. The bent-over position is what orients gravity to load the posterior deltoid through its actual line of pull. Some lifters use a slight forward lean as a compromise when the full hinge is uncomfortable, but the closer to parallel you can get, the more targeted the stimulus.