Reverse flys are a resistance exercise that work the major muscles of the upper back and the rear shoulders. The exercise can be done with dumbbells or resistance bands. The primary muscles worked during reverse flys are the rotator cuff and rear deltoids, and secondarily the trapezius. Other muscles worked include the rhomboids and latissimus dorsi. The exercise is great for targeting the posterior deltoid, which can be challenging to do with other exercises or machines. Performing reverse flys can improve your functional fitness level, promote an upright stance, and better posture in general. The exercise can also help increase activity in your deltoids and infraspinatus muscles.