Rear Delt Flys Muscles: Best Exercise-Focused Guide 2026

The rear delt flys muscles are crucial in developing strong, functional shoulders, a healthy posture, and a strong upper back. Rear delt flys muscles target your posterior deltoids, but also work the rhomboids and trapezius muscles. It’s important to strengthen these muscles to avoid shoulder weakness and poor posture. Utilising correct technique, light to moderate weights, and regular training makes it possible to grow this stubborn muscle. Work your rear deltoids with exercises such as dumbbells, cables, and machines, for optimal muscle engagement and long-term muscle strength.

Which Muscles Do Rear Delt Flys Target?

Primary muscles worked during rear delt flys are your posterior deltoid muscles, situated at the rear of the shoulders. These delts pull your arms back and assist with shoulder stability. But, there are other muscles involved when doing rear delt flys.

The rhomboids, which retract the shoulder blades, and the trapezius muscle, particularly the middle part, which supports the upper back, are also involved but to a lesser extent. Other tiny stabilizer muscles, such as the infraspinatus and teres minor, help to regulate the movement and protect the shoulder joint.

Rear delt flys muscles are primarily a shoulder muscle group, but also significantly use the upper back. Which is why some people aren’t sure if this is a shoulder or back exercise. The key is to do it right; otherwise, the focus can shift to the back.

This makes rare flies a complex exercise. The exercise works to strengthen shoulder stability and upper-back coordination, crucial aspects for posture and injury prevention.

Rear Delt Flys (Using Dumbbells)

It’s important to perform rear delt flys using good technique to engage the right muscles. Incorrect form can lead to a less effective workout and even injury.

Step-by-Step Instructions:

1. Grip a couple of dumbbells in a neutral position
2. Stand with a shoulder-width stance
3. Hinge at your waist, keeping your back straight
4. Let your arms hang straight down
5. Swing your arms out to your sides
6. Hold at the top and squeeze your shoulders
7. Slowly lower the weights back down

Key Form Insights:

When it comes to the best rear delt fly form, control is key. Elbows should be bent slightly, and your movements should be controlled. Don’t snap the weights or swing the dumbbells; this takes the focus off the target muscles.

A strong chest position and engaged core ensure that your rear delts remain the focus of the exercise. You should be engaging your rear delts and not your lower back and traps.

Rear Delt Fly Variations

When building rear delt flys muscles, it’s necessary to vary the exercise. These variations offer a different angle and/or resistance, so they all lead to better muscle recruitment.

1. Seated Rear Delt Fly

This version eliminates leg movement to better isolate. It is suitable for novices and people wanting to focus on form.

2. Cable Rear Delt Fly

The cables keep tension on the muscles for the entire exercise, so this is a great exercise for stressing the muscles.

3. Machine Rear Delt Fly

A guided and controlled movement in the correct direction. Very good for learning how to activate the proper muscles with rear delt flys.

4. Incline Bench Rear Delt Fly

This is done on the incline bench stability with your chest lying against it to reduce momentum.

5. Resistance Band Rear Delt Fly

An excellent exercise to do at home – no equipment required.

Benefits of Rear Delt Flys

There are many reasons to develop rear delt flys muscles.

1. Improved Shoulder Balance

Traditionally, most exercises work the front delts. Rear deltoid flies rebalance this.

2. Better Posture

Rounded shoulders are caused by weak rear delts. This helps improve shoulder posture.

3. Injury Prevention

The rear deltoid muscles help to steady the shoulder joint, preventing injuries while pressing or lifting overhead.

4. Enhanced Shoulder Size

Although the front and side delts help create shoulder width, the rear delt flys muscles help build thickness and bulk, creating a more visually appealing shoulder.

5. Upper-Back Strength

This exercise works the rhomboids and traps, too, enhancing the strength of the upper back. 

Common Mistakes to Avoid

• Using Too Much Weight: Excess weight may cause improper form and less muscle activation of rear delt flys. Controlling the weight with lighter weight is better.
• Swinging the Body: Momentum reduces muscle engagement. Move slowly and smoothly.
• Shrugging the Shoulders: This transfers stress to the traps.
• Not Squeezing at the Top: It’s important to contract. If you don’t do it, you don’t get the most from your workout.
• Rounding the Back: This will prevent injury to the spine and activate the correct muscles.

Best Rep Range and Sets

Moderate to high reps are best for posterior deltoid flys.

• Beginners: 2–3 sets of 10–12 reps
• Intermediate: 3-4 sets of 12-15 reps
• Advanced: 4–5 sets of 15–20 reps

Using a high number of reps will help develop muscle stamina and control, important for targeting the rear delts.

Where to Place Rear Delt Flys in Your Workout

Training of the rear delt flys muscles should be part of a well-rounded program.

Where to Place Them:

• As part of shoulder workouts
• During pull-day routines
• During upper-body workouts

Frequency:

For best results, it’s best to train your rear delts 2-3 times per week.

Rear delts are a common workout mistake. They are referred to as the forgotten muscle group, as they are not visible directly and need to be specifically targeted.

Why Rear Delt Flys Muscles Are Hard to Grow

Rear delt flys muscles are often considered the most difficult to grow muscles.
This is because:

• They are smaller than other shoulder muscles
• They are not heavily used in daily activities
• A lot of shoulder lifting exercises inadvertently favour other muscles

Rear delts need attention to proper form and technique. Failure to use proper form results in larger, stronger muscles (trap muscles) taking over, impeding growth.

Should I Do Rear Delt Flys?

Training your muscles using rear delt flys is well worth it. Your upper-body muscles play a crucial role in shoulder stability, posture, and strength.

Neglecting rear delt training can result in muscular imbalances, shoulder dysfunction, and injury. Strong rear delts are a part of a balanced and toned body.

Do Heavy Rear Delt Flys Work?

This exercise is not best suited to using heavy weights. This is an isolation exercise, so light weight is recommended with good form.
Heavy lifting often leads to:

• Momentum-based movement
• Reduced muscle activation
• Increased injury risk

Be slow and controlled, and contract muscles completely.

Do Rear Delts Make Shoulders Bigger?

Rear delt flys muscles play a major role in the shoulder muscles. Front and side delts make shoulders wide, while rear delts make them round.

Strong rear delts give a 3D look, adding volume and thickness to your shoulders.

Best Shoulder Exercises to Pair with Rear Delt Flys

For well-rounded shoulders, pair rear delt flys with:

1. Overhead Press

Builds full shoulder size and strength

2. Lateral Raises

Target side delts for the width.

3. Front Raises

Work front delts for balanced delts.

These three movements (and Rear delt flys muscles) make up a complete shoulder workout.

Best Dumbbell Shoulder Exercises

For weightlifters or bodybuilders, the most important exercises are:

• Dumbbell Shoulder Press
• Dumbbell Lateral Raises
• Dumbbell Rear Delt Flys

Both of the exercises engage the three different heads of the deltoids.

Are Rear Delt Fly Back or Shoulder?

Rear delt flys muscles are technically part of the shoulder muscl But they also work some of the upper back muscles, making the exercise confusing at times to determine whether it’s a back or shoulder movement.

The determining factor for focus is how they are performed. As long as you can control the movement – keeping your chest upright, a slight bend in the arms, and moving through the shoulder joint – muscles targeted for the rear delt flys exercise. You should feel the exercise in the back of your shoulders and not on your shoulder blades.

However, if you go too far back with the weights, squeeze too hard through the scapula (shoulder blades), or use momentum, the main focus will be the rhomboid and trapezius muscles, and it will feel more like a back move. This error is more typical when using heavier loads.
To work the desired rear delt flys muscles:

• Avoid excessive pull-back of the shoulder blades
• Keep the repetitions controlled and the distance less
• Focus on “lifting your arms,” not “pulling back.”

So rear delt flys are an upper back exercise with a strong shoulder emphasis. This site will show you how to work the rear delts. 

Slowest Growing and Hardest to Grow Muscles

Muscle growth is a fascinating process, and some muscles are easier to grow than others. The muscles worked when performing rear delt flys are considered to be one of the most difficult and slow to respond to stimulus.

First, the rear delts are small muscles in comparison to other muscle groups, such as the chest or legs. It’s simply harder for smaller muscles to gain mass. Second, they aren’t heavily used in functional movements, compared to muscles like the arms or legs. So they are almost exclusively stimulated by movements such as rear delt flys.

Third, compound exercises, like rows and presses, do not completely isolate the rear delt flys muscle. During these exercises, more dominant muscles (such as lats or traps) are often more activated, diminishing the effect on the rear delts.

Finally, a lack of mind-muscle connection can have an impact. It’s hard for some to get a good “mind-muscle” connection with their rear delts. This slows down development.
Other slow-growing muscles include:

• Calves, as they have a higher percentage of endurance fibres
• Forearms, owing to their being an overused muscle
• Lower abs, due to the need for a formidable posture and low body fat to see

Yet, the rear delt flys muscles are often a neglected part of the muscle. Regular training, form, and more repetitions are the key to success.

Exercises That Can Replace Rear Delt Flies

Although rear delt fly muscles are excellent, there are several exercises you can try to target the rear delts if you’re looking for variety or don’t have access to dumbbells.

Face Pulls

Face pull variations are a good substitute as they work both the rear delts and the upper back. This exercise focuses on creating shoulder stability and proper posture using a cable machine or band. Also, the natural pulling action with this exercise is less taxing on the shoulders.

Reverse Pec Deck

The reverse pec deck machine is machine-guided and a good exercise for beginners. It provides a constant tension on the rear delt flys muscles, and decreases momentum.

Bent-Over Rows (Wide Grip)

This exercise is more of a back movement, but achieving a wider grip and positioning your elbows in a flared-out position emphasizes the rear delts. This will engage rear delt flys and strengthen the upper back.

Resistance Band Pull-Aparts

This is a quick, easy exercise that can be performed at home or in the gym. It constantly engages the rear delts and is a great move for pre-workouts or high reps.

Such exercises are important as they vary the workout and avoid staling while still hitting rear delt flys muscles.

Exercises That Strengthen Rear Delts

For best results in building rear delt flys muscles, it’s important to include a mix of exercises that target the muscles with different angles and types of resistance.

Rear Delt Flies

This is the “core” exercise when it comes to the posterior deltoids. It permits fine control and isolation of the rear delt flys muscles.

Face Pulls

Face pulls are beneficial for strengthening the rear delts but also enhancing shoulder stability and posture. It’s a great exercise for counterbalancing pushing exercises.

Reverse Cable Crossovers

This exercise increases the tension on the muscle, making it more effective. It also provides more movement than dumbbells.

Incline Rear Delt Flys Delt Raises

This exercise can be done on an incline bench to reduce momentum and better isolate the rear delts. It’s particularly beneficial in building awareness.

Using both exercises, you’re taxing the rear delts at various angles, movement patterns, and resistance types. This promotes optimal growth and addresses the challenge of growing rear delts with flys.

Regular exercise, good form, and a varied routine ensure you build those stronger, defined rear delts.

Final Thoughts

Rear delt flys muscles are vital for shoulder balance and long-term health.  They are one of the most overlooked muscles, but essential for posture, injury, and aesthetic purposes.

Through fundamental form, regular exercise, and a variety of movements, you can target and develop well-developed rear delts. By performing rear delt flys regularly, you will not only boost your shoulder aesthetics but also your performance in other lifts.

Frequently Asked Questions

1. Are rear delt flys a shoulder or back exercise?

They focus on the shoulders but also involve the upper back muscles.

2. Should you do them?

Yes, they help with shoulder balance and posture.

3. How to do rear delt flys?

Keep weights light, slow, and squeeze the muscle.

4. Should I avoid rear delt exercises?

They can cause muscle imbalance and poor posture.