The rear delt cable fly is an isolation exercise designed to target the posterior head of the deltoid muscle, located at the back of the shoulder. This muscle group is often underdeveloped compared to the anterior (front) and medial (side) heads. Imbalances in shoulder development can contribute to poor posture and increase the risk of shoulder joint issues. Using the cable machine provides constant tension throughout the entire range of motion, benefiting muscle growth and joint health.
Cable Machine Configuration
The exercise uses a dual-pulley cable station, or cable crossover machine, with a single handle attachment on each side. For optimal alignment with the rear deltoid fibers, set the pulley height high, typically at or slightly above shoulder level. A high cable ensures the line of pull moves the arm in the plane of horizontal abduction, the primary function of the posterior deltoid. This upward angle also minimizes the involvement of the latissimus dorsi muscles.
Performing the Cross-Body Cable Fly Movement
Stand in the center of the machine and grab the handle opposite your hand (right hand takes the left cable, left hand takes the right cable). Step back slightly to create initial tension and adopt a staggered stance for stability. Extend your arms forward and crossed in front of your body, maintaining a slight, fixed bend in the elbows. This slight bend protects the elbow joint and keeps tension focused on the target muscle.
Initiate the fly by pulling your arms out and away from your center line in a wide, sweeping arc. The movement must be driven by the contraction of the rear shoulder muscles, not by the hands or biceps. Pull until your hands are roughly in line with your shoulders or slightly behind the plane of your torso. This position represents the peak contraction, where the posterior deltoid is fully shortened.
The return phase, or eccentric portion, must be slow and controlled, resisting the cable’s pull back to the starting position. This deliberate tempo maximizes the time the muscle spends under tension, stimulating muscle growth. Allow your arms to return to the fully stretched, crossed position before beginning the next repetition.
Ensuring Proper Form and Maximizing Muscle Isolation
A common error compromising rear delt isolation is using excessive weight, which leads to momentum and body swinging. When the load is too heavy, the stronger trapezius and rhomboid muscles take over, turning the fly into a partial row. Select a light resistance that allows you to control the weight through the full range of motion, ensuring the rear delts perform the work.
Avoid excessive shoulder blade retraction, or squeezing the shoulder blades together, as this shifts focus to the upper back muscles. Instead, focus on moving only the upper arm bone (humerus) in the shoulder socket, minimizing shoulder blade movement. Do not bend the elbows significantly during the pull, as this recruits the triceps and reduces leverage on the rear deltoid. Maintain a stable, braced torso to prevent rocking or arching of the lower back, isolating the force to the shoulder girdle.
Integrating the Rear Delt Fly into Your Training
The rear delt cable fly is best used as an accessory lift, typically performed later in a back or shoulder workout. Since the posterior deltoid is a small muscle group that recovers quickly, it responds well to higher repetition ranges. Aim for 12 to 20 repetitions per set, the range recommended for isolation exercises to maximize blood flow and metabolic stress.
The focus on lighter weight and higher reps means this exercise targets hypertrophy and muscular endurance, not maximal strength development. Due to the muscle’s size and recovery profile, the rear deltoids can be trained frequently, often two to three times per week. Consistent, high-quality volume is more effective than infrequent, heavy attempts, especially when correcting a muscle imbalance.