Rear Delt Fly: How to Do It, Muscles Worked and Form Tips

The rear delt fly is a small movement that solves a big problem. Most of us press, sit and stare at screens far more than we pull, which leaves the back of the shoulder weak and the posture rounded forward. The rear delt fly targets exactly that neglected muscle, the posterior deltoid, along with the upper-back muscles that pull your shoulder blades together. It is also the piece most people are missing if they want fuller, more three-dimensional shoulders rather than just big fronts. Here is how to do it properly with dumbbells, cables or a machine, the muscles it works, and how to actually feel it in the right place.

How to do a rear delt fly

You can do this with a pair of dumbbells, a cable machine or a reverse pec deck. The dumbbell version is the most common at home, so we will start there.

1. Set your position. Sit on the end of a bench or stand with your feet hip-width apart. Hinge forward from the hips until your chest is close to parallel with the floor, letting the dumbbells hang straight down under your shoulders. Keep a long, flat back, not a rounded one.
2. Set your arms. Turn your palms to face each other and put a slight, fixed bend in your elbows. That elbow angle stays the same for the whole rep, so you are not curling or pressing.
3. Raise the weights. Lead with the backs of your hands and your elbows, spreading your arms out to the sides in a wide arc until they are roughly level with your shoulders. Think about the movement coming from the back of your shoulders, not your hands.
4. Pause and squeeze. Hold for a beat at the top. You should feel it across the back of the shoulders and upper back, not in your lower back or neck.
5. Lower under control. Bring the weights back down slowly along the same arc. Do not let them drop. That slow lowering is where a lot of the benefit lives.

Muscles worked

The rear delt fly is a horizontal abduction movement, which means it draws your arms out and back against resistance. That pattern loads the back of the shoulder and the muscles between the shoulder blades.

• Posterior deltoid. The main mover, sitting at the back of the shoulder. Research analysing the three heads of the deltoid confirms that horizontal abduction movements like the reverse fly are among the most effective ways to target the posterior portion (analysis of deltoid activation across exercises).
• Rhomboids and mid to lower trapezius. These upper-back muscles retract and stabilise your shoulder blades as your arms travel outward, which is why the exercise feels as much like a back movement as a shoulder one.
• Rotator cuff (infraspinatus and teres minor). These small stabilisers help externally rotate and control the shoulder, and they are the muscles that keep the joint healthy.
• Grip and forearms. They hold the dumbbells, though the loads are light enough that grip is rarely the limit.

A small detail changes the emphasis: using a neutral grip, palms facing each other, tends to bias the rear delt more than a fully pronated, palms-down grip. One study on posterior shoulder exercise found greater posterior deltoid activity with a neutral hand position than a pronated one (hand position and posterior shoulder muscle activity).

Benefits

• It builds the shoulders you actually see from the side and back. Big front delts without rear delts look flat. Adding rear delt work rounds out the shoulder and gives it a fuller, more balanced shape.
• It supports better posture. Strengthening the rear delts and shoulder-blade retractors counterbalances the rounded-forward posture that desk work and pressing encourage.
• It looks after your shoulders. A strong, balanced shoulder with a working rear delt and rotator cuff copes better with pressing and overhead work, which is where a lot of gym niggles start.
• It needs almost no kit. A pair of light dumbbells and a bit of floor space is enough, so it slots easily into home training.

Common mistakes

Going too heavy. This is the big one. The rear delts are small, so a heavy dumbbell just recruits your traps, lower back and momentum. Use a light weight you can control and feel.

Turning it into a row. If your elbows bend and drive back behind you, you are rowing, not flying. Keep a fixed, soft bend in the elbow and lead with the elbows out to the sides.

Shrugging. Letting your shoulders creep up towards your ears hands the work to your upper traps. Keep your neck long and your shoulders down away from your ears throughout.

Using your lower back. Swinging your torso up to help lift the weight loads your lower back and takes tension off the target. Brace your core, keep the hinge still, and move only your arms.

Variations

• Dumbbell rear delt fly. The standard version above, seated or standing. Easiest to set up at home with a pair of adjustable dumbbells.
• Reverse pec deck. A machine version that supports your chest and locks in the path, so it is easy to feel the rear delts. Great for beginners and for going to higher reps.
• Cable rear delt fly. Using a cable machine with the pulleys set high keeps constant tension through the whole range, which many people find gives the best mind-muscle connection.
• Bent-over reverse fly on an incline bench. Lie chest-down on an incline bench to remove any lower-back involvement and cheating.

A simple sets and reps plan

Rear delts thrive on volume and control rather than heavy loads. Add two to four sets of 12 to 20 reps at the end of your upper-body or shoulder days, two or three times a week. Keep the weight light enough that the last couple of reps are hard because the muscle is tired, not because you are swinging. The NHS recommends muscle-strengthening work for all the major muscle groups on at least two days a week, and rear delt flys are an easy way to make sure the back of the shoulder is not the group you skip.

Pair them with pulling movements for a balanced, healthy shoulder. Face pulls hit similar muscles from a different angle, and rowing exercises like the bent over row train the wider back. Round out your shoulder training with lateral raises for the side delts and pressing for the front.

Recommended reads

• Rear delt exercises
• Face pulls
• Lateral raises
• Best adjustable dumbbells UK
• Workout guides