The rear delt fly is a resistance exercise designed to isolate and build the muscles on the back of the shoulder. This movement is a popular tool for developing a balanced shoulder girdle, often neglected in favor of the larger chest and front shoulder muscles. The question of whether it is a “push” or a “pull” exercise frequently arises because the action feels different from traditional pressing or rowing movements. Understanding the muscles involved and the direction of force is necessary to properly classify and program this movement.
Anatomy of the Rear Delt Fly
The primary muscle targeted during the rear delt fly is the posterior deltoid, which forms the rear portion of the shoulder cap. This muscle is responsible for horizontal abduction, the action of moving the arm away from the midline of the body in the horizontal plane. This action occurs when the arms are pulled backward in the fly motion. The posterior deltoid is often under-developed compared to the anterior and medial heads of the shoulder.
Several synergistic muscles assist the posterior deltoid. The rhomboids and the middle and lower trapezius muscles, located in the upper back, work together to retract the scapulae, or squeeze the shoulder blades together. This scapular retraction stabilizes the shoulder joint and ensures the posterior deltoid contracts effectively. The rotator cuff muscles, specifically the infraspinatus and teres minor, also stabilize the shoulder and assist with external rotation of the arm.
Movement Mechanics: Why the Rear Delt Fly is a Pull
In resistance training, exercises are broadly categorized based on the direction of force relative to the body’s center mass. A “push” movement involves pushing resistance away from the torso, utilizing muscles like the chest, triceps, and anterior deltoids. Conversely, a “pull” movement involves drawing resistance toward the body, engaging muscles in the back, biceps, and posterior shoulder.
The rear delt fly is classified as a pull exercise. This classification is based on the action of the working muscles, which exert force to draw the weights or handles toward the upper back and spine. Whether performed bent-over with dumbbells or on a machine, the user is actively pulling the resistance to spread the arms laterally behind the body. This movement pattern directly contrasts with pushing actions like the overhead press or bench press, where the weight is moved away from the body.
The confusion often stems from comparing the rear delt fly to other lateral movements, such as the side lateral raise, which targets the medial deltoid. The side lateral raise is an abduction movement that does not involve drawing the weight toward the body’s midline. However, the rear delt fly is a horizontal abduction that pulls the arms back. Focusing on the muscles on the back of the body contracting to retract the arms clarifies the pulling nature of the exercise.
Integrating Rear Delt Work into Training Splits
Since the rear delt fly is a pull movement targeting the back and posterior shoulder muscles, it is best integrated into the “Pull Day” of a Push/Pull/Legs (PPL) split. This strategy groups exercises by their movement pattern, allowing pushing muscles to rest while pulling muscles are worked. Placing the rear delt fly here ensures the posterior deltoid is trained alongside other major pulling muscles like the lats and rhomboids.
In a different structure, such as a body part split, the rear delt fly is traditionally performed on a “Back Day” or a dedicated “Shoulder Day.” For optimal development, direct rear delt work is often combined with compound back exercises like rows and face pulls, as these also engage the posterior shoulder. Proper placement helps ensure a balanced approach to upper body strength, counteracting the emphasis often placed on anterior pushing movements that can contribute to rounded shoulders and poor posture.