What Muscles Do Flat Flyes Work?

You may include flat chest flyes into your workout without truly understanding how they benefit your body. The move, done with dumbbells on a flat bench, primarily targets the pectoralis major – the main chest muscle. When designing a chest workout, realize that flat bench flyes may not be the most effective way to build strength in your chest, however.

To perform a flat fly, lie on your back on a weight bench holding a dumbbell in each hand. Extend your elbows, leaving them slightly bent, and have your palms face each other – the elbows should point out to the sides. With an arclike motion, open your arms to lower the dumbbells to the point at which they are parallel to the top of the bench. Draw your arms back together until the dumbbells nearly touch to complete one repetition.

The primary muscle activated during the fly is the pectoralis major. This large, fan-shaped muscle makes up the front of the chest wall and is responsible for pushing movements as well as movements that make the arms move toward the back of the body. The pectoralis has two major heads: the clavicular at the upper part of the chest and the sternal at the lower part of the chest. The fly targets primarily the sternal head.

A number of muscles act in conjunction with the pectoralis major to create the flying motion. The clavicular head of the pectoralis major and the anterior deltoids at the front of the shoulders, for example, are quite active during the fly. The short head of the biceps, the brachialis at the forearm, the triceps and the wrist flexors also assist.

When it comes to chest exercises, the flat fly may not be the best exercise to target the pectoralis major. The May 2005 issue of the “Journal of Strength and Conditioning Research” reported a study showing that flyes activated the pec muscle for less time than barbell or dumbbell bench presses. The Truman State University Researchers recommended that it be used as an auxiliary lift, rather than a primary lift, when training the chest. The American Council on Exercise also recommends that you use the barbell chest press, pec dec machine or bent-forward cable crossovers as the primary exercises to target the pectoralis major.