Chest Fly

Chest flyes performed on a machine, also referred to as a “pec deck”, are a resistance exercise. This exercise involves the primary horizontal shoulder adductor, the pectoralis major. This exercise is performed seated on the fly machine while bringing arms forward in an arc movement.

The concentric portion of the lift is horizontal shoulder adduction. The concentric portion involves the lifting of the weight. The eccentric portion is horizontal shoulder abduction, which involves the descent of the weight.

The purpose of the chest fly machine is to strengthen the pectoralis major while promoting hypertrophy (increases in size) of this muscle.

Chest flyes on a machine increase the size and strength of the upper (clavicular) and lower (sternocostal) heads of the pectoralis major. Chest flyes entail a stretch of the pectoralis major as the arms are fully abducted, resulting in significant activation of the pectoralis major fibers as the arms adduct. Chest flyes particulary activate the outer fibers of the pectoralis major. This includes the fibers that form the axilla (the front of the “arm pit”). Like the bench press, chest flyes are a staple exercise to develop the chest.

The long head of the triceps, anterior deltoid and middle deltoid are also activated in this movement.

Performing chest flyes on a machine allow the lifter to execute the fly from a vertical position and seated. The pulley system of the machine also provides a uniform resistance throughout the entire range of motion.

Chest flyes on a machine serve as a valuable exercise to improve aesthetics of the pectoral muscle.

The pectoralis major is a large, fan-shaped muscle that spans across the chest, forming the front portion of the axillary fold (arm pit). It is divided into two parts: clavicular and sternal. Its origin is located at the sternal end of the clavicle, the sternum, rib cartilage (ribs 1-6 [or 7]), and the aponeurosis of the external oblique. The fibers of the pectoralis major converge at the point of insertion located at the greater tubercle of the humerus. The pectoralis major aids in pushing movements as the shoulder adducts the arm against resistance. The shoulder horizontally adducts as the handles follow through the arc pattern forward.

The vertical positioning of this exercise targets both the sternocostal and clavicular heads of the pectoralis major. Machine chest flyes are an effective exercise for developing the entire chest.

The triceps brachii is located on the back of the upper arm, originating at the shoulder and inserting in the elbow joint. It consists of three heads, the long, medial and lateral head. The medial head lies beneath the long and lateral head. The long head origin is located at the infraglenoid tubercle of the scapula (shoulder blade). The original of the lateral head is located at the posterior shaft of the humerus. The medial head origin is located at the radial groove of the posterior humeral shaft.

The long and lateral heads make up the “horseshoe” portion of the triceps. All three heads merge, sharing insertion into the olecranon process of the ulna, located at the elbow joint.
The triceps brachii extend the elbow joint. The long head assists in arm adduction when executing the chest fly.

The deltoid is a thick, multipennate muscle that forms a curtain around the shoulder. It is the primary muscle involved with arm abduction and the anterior fibers are a primary shoulder flexor. The anterior deltoid is a primary synergist of the pectoralis. When developed, the deltoids give the shoulder their round shape. The origin of the deltoid is located at the insertion of the trapezius, lateral third of the clavicle and the acromion spine of the scapula. Its insertion is located at the deltoid tuberosity of the humerus.

Like the anterior fibers of the deltoid, the coracobrachialis is a synergist pectoralis major with horizontal shoulder adduction. It is a small muscle originating at the coracoid process of the scapula and inserting half way down the shaft of the humerus.

The wrist flexors stabilize the wrists and the rotator cuff muscles stabilize the shoulder girdle.

Dumbbell chest fly, gorilla fly, lying cable fly, high pulley cable fly, low pulley cable fly, chest height pulley cable fly.

When lowering the weight during the eccentric phase, extending the elbow (opening the arms) slightly will allow for a greater stretch on the pectoralis major before proceeding to lift the weight. This will increase pectoralis major fiber activation. Experienced lifters should only do this as it may increase the risk of injury to the shoulder joint.

For optimal results, strategically incorporate chest flyes at a cable crossover station (e.g. low pulley cable fly, lying cable fly) and with free-weight dumbbells (e.g. dumbbell chest fly, gorilla fly) in your chest training regimen. Activating pectoralis major fibers from a variety of angles maximizes strength and hypertrophy gains.

To minimize negative stress on your shoulder joint, do not allow the upper arms to extend behind the line of the shoulder and torso.

Focus on the concentric portion of the contraction, concentrating on “squeezing” as you bring the handles together in front of you.

Emphasis on eccentric contractions, prolonging the eccentric portion of the contraction, may also be incorporated in a training program focused on increasing strength. This should be implemented accordingly and with adequate muscle recovery as eccentric contractions cause substantial damage to muscle tissue.

It is important to note that your repetition and set volume will depend on your goals (e.g. strength, hypertrophy, muscular endurance). It is also important to allow adequate recovery days in between chest and triceps training to allow muscles to repair.

On the eccentric phase, bringing your shoulders behind your torso should be avoided as it results in excessive horizontal shoulder abduction. This can place great stress on the shoulder joint. Ensure that the upper arms do not go behind the torso when opening your arms while lowering the weight. 1

Bouncing at the bottom of the movement or forcefully bringing the handles together is unnecessary and may increase the risk of injury. Ensure that both concentric and eccentric phases of this exercise are controlled and momentum is minimized.

1. Reinold MM, Gill TJ, Wilk KE et al. (2010). Current concepts in the evaluation and treatment of the shoulder in overhead throwing athletes, Part 2. Sports Health. 2(2):101-115.

If proper technique is not adhered to (e.g. lowering the upper arms past the level of the torso, dropping the weight quickly instead of controlling the descent on the eccentric portion of the lift), the likelihood of injury increases.

If proper technique and recovery are not adhered to, impingement syndrome, rotator cuff injuries, pectoralis major tears and/or glenoid labrum tears may result. It is best to avoid chest fly exercises when addressing impingement syndrome/rotator cuff injury unless advised by a physical therapist.