Building a strong, toned upper body is something most people think about when they think about sculpting their upper body—but your back needs equal attention. A balanced body isn't just about looks; it's also about posture, preventing injury, and functional strength overall. That's where the Back Butterfly Workout, or Reverse Pec Deck, comes in.

This underappreciated exercise engages the posterior deltoids, trapezius, and rhomboids—the muscles responsible for a toned upper back and better posture. Whether bodybuilder or simply someone wanting to correct their desk slump, this exercise has a spot in your arsenal.

What Is the Back Butterfly Exercise?

Back Butterfly is an exercise done on a pec deck machine, but instead of pushing towards each other as you would with a chest fly, you reverse it—reverse the movement. You sit facing the pad and draw the handles out and away from you, simulating the motion of stretching wings—thus the name.

Muscles Worked

Posterior Deltoids (back shoulders)

Rhomboids (mid-between shoulder blades)

Middle Trapezius

Teres Minor and Infraspinatus (both rotator cuff muscles)

These muscles are usually overlooked in general routines, but they are essential to shoulder stability, posture adjustment, and keeping that slouchy look away.

Why You Should Add It to Your Workout

1. Better Posture

If you're stuck for hours on end sitting or staring at a screen, there's a good bet that your shoulders are rounding forward. The back butterfly reverses that by strengthening the muscles that retract your shoulders.

2. Improved Shoulder Health

Developing the rear delts and rotator cuff muscles makes the joint more stable and improves the likelihood of not getting hurt while performing other exercises for the upper body.

3. Balanced Physique

Excessively developing your chest can create imbalances. The back butterfly supports symmetry and a well-balanced, beautiful body by building your upper back.

4. Isolation and Control

This exercise, unlike compound lifts such as rows or pull-ups, lets you isolate certain muscles and concentrate on form and mind-muscle link.

How to Do the Back Butterfly Properly Step-by-Step:

Adjust the Machine:

Sit on the pad, facing it, with feet on the floor. Set the seat so the handles are at shoulder level or just below that.

Set Your Position:

Take the handles with palms turned in, neutral grip. Keep elbows slightly bent.

Engage Your Core:

Sit up straight, chest to the pad, and tighten your core to keep from using momentum.

The Movement:

Slowly open your arms in a wide arc, squeezing your shoulder blades together at the end of the motion. Hold for a second.

Controlled Return:

Bring your arms back to the starting position under control. Avoid letting the weights slam or bounce.

Reps and Sets:

Try 3–4 sets of 12–15 reps with moderate weight. Focus on form over weight—you’ll get more benefit from a controlled squeeze than from heavy, sloppy reps.

Common Mistakes to Avoid

Swinging the body or using momentum

Locking out or overextending elbows

Not squeezing shoulder blades

Shrugging shoulders up towards ears

Variations and Alternatives

If you don't have a pec deck machine, here are a few good alternatives:

Reverse Dumbbell Flys (standing bent-over or on a bench)

Cable Reverse Flys

Resistance Band Pull-Aparts

Face Pulls with rope attachment

Final Thoughts

The Back Butterfly Exercise is not as glamorous as a pull-up or bench press, but the advantages are undeniable. It's one of the best exercises for building your rear delts, mid-back musculature, and postural strength. It also helps achieve that much-desired V-taper look in the rear view.

Include this exercise in your upper body workout 1–2 times a week, and you'll find after a while not only cosmetic differences, but a more solid, assertive posture as well.

Sculpt Your Upper Body with the Back Butterfly Workout: Form, Benefits, and Tips