The back fly, often called the Bent-Over Fly, is an isolation exercise designed to strengthen the muscles of the upper back and the rear portion of the shoulder. This movement involves raising weights out to the sides while the torso is bent forward, targeting the muscles responsible for pulling the arms backward and the shoulder blades together. Regularly performing this exercise helps add thickness and definition to the upper back while contributing to shoulder health and better posture. It is an effective way to balance the strength developed by common pressing movements.
Primary Muscles Targeted
The primary goal of the back fly is to engage the Posterior Deltoid muscle, which forms the rear head of the shoulder and is the main muscle responsible for the arm’s horizontal abduction. This muscle initiates the lift as the arms move out and up toward shoulder level. Because the posterior deltoids are small muscles, the exercise requires lighter weights and a strict focus on form to ensure they are fully activated.
Working in conjunction with the deltoids are the Rhomboids and the Middle Trapezius. The rhomboids, located beneath the trapezius, work to retract the scapulae, pulling the shoulder blades toward the spine. The middle trapezius fibers assist in this retraction, effectively pinching the shoulder blades together at the peak of the movement. Prioritizing this scapular retraction is necessary for maximizing thickness and strength in the upper back.
Supporting Muscles Engaged
To execute the movement effectively, several smaller muscle groups and stabilizers must also be engaged. The four muscles of the Rotator Cuff—the supraspinatus, infraspinatus, teres minor, and subscapularis—work dynamically to stabilize the shoulder joint. This stability is required to safely move the arm through the horizontal plane, preventing unwanted rotation or impingement.
The Erector Spinae muscles, which run vertically along the spine, are active throughout the exercise to maintain the bent-over torso position. They contract to prevent the back from rounding forward under the pull of gravity and the weight. Furthermore, the muscles of the forearm, including the flexors and extensors, must work to maintain a secure grip on the dumbbells throughout the entire range of motion.
Executing the Movement Safely
Proper execution begins with the correct setup: standing with feet shoulder-width apart and a slight bend in the knees. The lifter must hinge forward at the hips, keeping the back straight and neutral, until the torso is near parallel to the floor. This deep hinge aligns the resistance vector of gravity with the muscle fibers of the rear deltoids.
To start the lift, the movement should be initiated by pulling the elbows out and up, rather than simply lifting the hands. Maintain a slight, fixed bend in the elbows and raise the dumbbells only until the arms are level with the shoulders, reaching the horizontal plane. Going higher than this point can cause the upper trapezius to take over the work, shifting the focus away from the rear deltoids.
Use a controlled tempo, avoiding the use of momentum to swing the weights up. The weights should be lowered slowly back to the starting position, maintaining tension on the target muscles during the eccentric phase of the movement. If the bent-over position is challenging to hold with a neutral spine, the exercise can be performed seated or using an incline bench to support the torso.