Reverse flys mainly work the rear delts (the back of your shoulders) and the upper back —especially the rhomboids and middle traps. They also help the rotator cuff muscles stabilize the shoulder.

What they’re good for

  • Better shoulder balance: They train muscles that often get neglected compared with pressing movements.
  • Posture support: Stronger upper-back muscles can help you keep your shoulders from rounding forward.
  • Shoulder stability: The rotator cuff helps control the movement and support the joint.

Simple form cue

Think: “Open your arms wide, not shrug your shoulders.” Keep a slight bend in the elbows and move slowly with control.

Quick takeaway

If you want a short answer: reverse flys are a rear-delt and upper-back exercise, with extra help from the traps, rhomboids, and rotator cuff.