Brenda Spriggs, MD, MPH, MBA
The pec fly machine, also called the pec deck fly machine, is a type of gym equipment that targets the pectoral muscles in the chest. While primarily working the pectoralis major muscles, using a pec fly machine requires some support from the pectoralis minor muscles in the chest, the deltoid muscles in the shoulders, and the serratus muscles in the rib cage. Building strong chest muscles with exercises such as the pec deck fly is important for movements involving the upper body. This type of exercise also influences the shape and appearance of the upper body.
The pectoralis major muscles targeted by the pec deck fly serve as an important muscular link from the thorax to the upper arm. The main function of these muscles is to complete motions involving adduction and medial rotation of the arms. The pectoralis major muscles are also among the most noticeable body parts, so by doing exercises that target this set of muscles, you can favorably influence the appearance of your physique. The pectoralis minor, serratus anterior and deltoid anterior muscles act as synergists when using the pec deck fly machine, meaning that they help support the motion of the pectoralis major muscles. Besides assisting the pec major muscles, having strong pec minor, serratus and deltoid muscles is important for shoulder and shoulder blade movements.
The pec deck fly is an isolation exercise, meaning it involves just one major joint movement. The movement is a squeezing motion in which the arms are pressed together toward the center of the body. This contraction is achieved by pushing your arms against the pec fly machine's levers, which control an adjustable weight. With steady application of pressure, the machine keeps the arms moving in an arc motion until both arms meet in front of the chest. By slowly releasing this contraction, the weight is lowered back to the starting position, completing the repetition. Using a pec deck fly machine is safer and and easier than doing flys using free weights, since it doesn't require particularly good balance or muscle control.
While the pec deck fly machine is relatively safe and easy to use, it still requires proper technique. Part of good pec deck fly machine technique includes proper positioning of the body in relation to the machine. Before starting a repetition, you should be sitting up straight with your back against the seat, your forearms on the padded levers, and your upper arms positioned relatively parallel to the floor. It is also important that the shoulders are not hyperextended in the starting position. When completing a rep, move the arms slowly and steadily rather than in a fast, jerky manner. If you are unable to maintain the contracted position for a count of two seconds, you are using too much weight and should lower the weight setting.
Variations and Other Pec-Strengthening Exercises
According to an article by weightlifter Lynn Glenn, some variations of the pec deck fly include the pec fly with dumbbells, the chest press machine, and the pec fly with a resistance band or cables. The pec deck fly also complements other compound exercises that target the pectoral muscles, including the bench press. Besides the pec deck fly and its variations, other exercises that work the pectoral muscles include the incline bench press, decline bench press, machine dips and push-ups.