Dumbbell flyes are an isolation exercise that targets the chest. The term "isolation" means that there is movement at only one joint -- not that any single muscle is worked on its own. All movements rely on a synergistic combination of muscles. You can perform dumbbell flyes using an incline, decline or flat bench, which place a slight emphasis on the upper, lower or middle fibers of the chest, respectively. You can also perform flyes using cables for variation.
Pectoralis Major
The agonist or main muscle used in the flat dumbbell flye is the pectoralis major, or pecs for short. This large, fan-shaped muscle is located on the front of your upper torso and is responsible for drawing your arm inward in a movement called horizontal flexion. Many exercisers, especially men, want to develop bigger pecs; dumbbell flyes are a popular exercise for this purpose.
Anterior Deltoids
Working with your pecs to horizontally flex your shoulder, your anterior deltoid is located on the front of your shoulder. This small but powerful muscle is involved in all pressing and flying-type movements including shoulder presses, pushups and the bench press. The anterior deltoid is one of a group of three major shoulder muscles: the medial and posterior deltoids being the other two.
Biceps Brachii
Meaning two-headed arm muscle, your biceps brachii crosses your elbow and your shoulder. As dumbbell flyes involve very little elbow movement, but a large range of movement at the shoulder, the short head of the biceps contributes to the action of shoulder flexion. The biceps brachii is also involved in holding your elbow rigid when you perform flyes. This type of muscle action is called an isometric contraction. Although not involved in the action at the shoulder, your triceps brachii also work isometrically to help maintain rigid elbows.
Rotator Cuff
The rotator cuff is the collective term used to describe four small but very important muscles that control many of the movements of your shoulder joint: supraspinatus, infraspinatus, terres minor and subscapularis. Sometimes referred to as the SITS muscles, the rotator cuff provides vital stability for the ball and socket joint that is your shoulder. The rotator cuff is prone to injury and because the SITS muscles are located deep within the shoulder joint, treatment can be very difficult. Baseball players and weight lifters are especially prone to rotator cuff injuries. Minimize your injury risks by only lowering the dumbbells so that they are level with your shoulders and never bouncing out of the bottom of this exercise.
References
- "Atlas of Skeletal Muscles by Robert J. Stone and Judith A. Stone"; 2008
- "Anatomy of Exercise: A Trainer's Inside Guide to Your Workout"; Pat Manocchia; 2009
- "Strength Training Anatomy"; Frederic Delavier; 2010
- "Dumbbell Training for Strength And Fitness"; Matt Brzycki and Fred Fornicola; 2006
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