What muscles does the rear delt fly work?

The rear delts at the back of the shoulder, and the upper back between the shoulder blades.

Do I need rear delt flies if I do rows?

Rows work the rear delts a little, but mainly train the upper back and lats. A direct exercise like the rear delt fly or the face pull is the simplest way to give the back of the shoulder its own work.

How heavy should rear delt flies be?

Light. Many experienced lifters use 4 to 10 kg dumbbells. If you need to swing or bend your elbows more to finish the rep, it is too heavy.

Rear delt fly or face pull?

Both train the rear delts. The face pull adds outward rotation of the upper arm; the rear delt fly isolates the back of the shoulder more. Many programmes use one or alternate them.

Rear Delt Fly: Muscles Worked and How to Do It

Rear delt fly: muscles worked and how to do it

The rear delt fly trains your shoulders, specifically the rear delts at the back of the shoulder, and your upper back. It is an isolation exercise: your arms sweep out to the sides with the elbows slightly bent, the opposite of a chest fly.

You can do it bent over with dumbbells, with cables, or on a reverse pec deck. The rear delts are small and get little direct work from rows and presses, which is why many programmes add this exercise for rounder, more balanced shoulders.

At a glance

Main muscles: Shoulders
Upper back
Movement: Pull the arms back and apart
Equipment: Dumbbells, Cable machine, Machine
Type: Isolation (one joint)

Front

Back

How to do a rear delt fly

Hold a light dumbbell in each hand and hinge forward from the hips until your torso is close to parallel with the floor, back flat, knees soft. Let your arms hang below your shoulders, palms facing each other.
Bend your elbows slightly and keep that bend throughout.
Raise your arms out to the sides in a wide arc, leading with the backs of your hands, until your arms are about level with your torso.
Pause briefly without squeezing your shoulder blades hard together.
Lower the dumbbells slowly back to the start.

Cues that help

"Out, not back": push the dumbbells out to the walls rather than pulling them up behind you.
"Pinkies lead": a slight turn of the hands helps the rear delts take the work.
"Still torso": your back angle stays the same; if you bob up, the weight is too heavy.
"Shoulders away from the ears": no shrugging.

Common mistakes

Turning it into a row: bending the elbows more and pulling back, which hands work to the upper back and lats.
Squeezing the shoulder blades hard together at the top. Keep the movement in the shoulders.
Swinging the torso up to throw the weight.
Using weights that are too heavy. The rear delts are small; very light dumbbells are normal.

Dumbbells, cable or machine?

Bent-over dumbbells need nothing but a pair of weights but ask your lower back to hold the position. A reverse pec deck supports your chest, so you can focus on the shoulders. Cables, crossed from two high or shoulder-height pulleys, keep tension through the whole range.

All three train the same muscles. If your lower back tires before your shoulders, use the machine or a chest-supported version on an incline bench.

Sets, reps and weight

For muscle: 3 to 4 sets of 12 to 20 reps.
Rest about 1 minute between sets.
Pick a weight you can raise without swinging and lower in two seconds.
They fit at the end of an upper-body or shoulder session.

Variations and alternatives

Reverse pec deck: seated, chest against the pad, handles in front of you.
Chest-supported rear delt fly: lying face down on an incline bench.
Cable rear delt fly: cables crossed in front of you, pulled out to the sides.
Face pull: the rear delts plus the muscles that turn the arm outwards.
Lateral raise: the same idea upright, for the side of the shoulder.

Tracking your rear delt flies

PushBeyond logs the weight and reps of each set and charts the history of the exercise. Its muscle map counts the rear delt fly for your shoulders and upper back.