Rear delt fly: how to do it.
The rear delt fly trains the posterior deltoid, the most forgotten muscle in the body: it's out of sight in the mirror, and no pressing movement touches it. Too bad, because without it your shoulders look flat from the side and your posture drifts forward. Five minutes a week fixes both.
Starting position
- Bend your torso forward until it's almost parallel to the floor (standing with hips back, or seated on the edge of a bench).
- LIGHT dumbbells under your chest, palms facing each other, elbows slightly bent.
- Neutral spine, neck in line: your gaze goes to the floor.
Proper form
- Open your arms out to the sides in a wide arc, leading with your ELBOWS.
- Raise until your elbows reach shoulder height, no higher.
- Lead slightly upward with your pinky finger: this maximizes posterior deltoid activation.
- Pause briefly at the top, without fully squeezing your shoulder blades together (that's rhomboid work).
- Lower over 2-3 seconds, resisting the weight, back down under your chest.
When to inhale, when to exhale
Exhale as you open, inhale as you lower. The bent-over position calls for short, steady breaths: never hold your breath for long in this position.
Mistakes to avoid
Bouncing your torso turns the fly into a lower-back swing. Lock your torso at parallel and keep it there: if you need to stand up to finish the rep, the dumbbell is too heavy.
If your shoulder blades come fully together, the work shifts to your rhomboids and traps. To isolate the rear delt, keep your shoulder blades "wide": only the arm should move.
The rear delt is smaller and weaker than the lateral one: it needs lighter dumbbells and higher reps. Ego has nothing to gain here: nobody sees how much weight you're using.
DAWT tip. The posterior deltoid responds to volume and frequency: 12-20 reps, even every other day, with a weight that lets you pause at the top. If it's not burning behind your shoulder after two sets, it's not a rear delt fly, it's something else.
Variations and alternatives
Quick answers
Why train the posterior deltoid?
For aesthetics (the "3D" shoulder look from the side), for posture (it counters the forward hunch from desk work and pressing), and for shoulder health (it balances out pressing movements). It's small, but it changes everything.
Rear delt fly or face pull, which is better?
They work the same area in complementary ways: the fly isolates more, the face pull adds the rotator cuff. Alternate between them or do both: total volume for the rear delt is never too much.
Related exercises
How much should you load on this exercise?
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