Let’s look at dumbbell flyes.
Primary muscles targeted include the chest and shoulders. Dumbbell flyes also engage the upper back and biceps secondarily, as stabilizing muscles.
The rotator cuff and back of the shoulders are worked, as well as the serratus anterior, a muscle along the rib cage that helps to keep the shoulders in proper alignment.
Lie on your back on a firm surface, such as a bench or the floor. If on the floor, bend the knees. If using a bench, keep your feet on the floor.
If your back arches when using a bench, you can place the feet on a slightly raised platform to help keep the spine in a neutral to flat position.
Lowering phase: Hold the dumbbells over your chest, arms up and hands facing each other, then slowly lower the arms until they are level with your shoulders or chest. The arm position used resembles the same as if giving a big hug, with just a slight bending of the elbow. Keep your feet firmly on the floor throughout the exercise.
Lifting phase: Slowly bring the arms back up into the starting position, keeping the same slight bend at the elbow, with wrists in a neutral position.
When performing flyes, do not lock out the arms. Instead, leave a slight bend at the elbow.
Keep your back in its normal neutral position and your arms slightly beneath the shoulder joint.
Ensure that you don’t hunch your shoulders while performing the exercise. Instead, pull the shoulder blades slightly down and back so that they make firm contact with the floor or bench.
Most dumbbell flyes are performed on a flat bench or floor, but they also can be performed on an incline surface. Using an incline bench stresses the upper chest and front of the shoulders to a greater degree, so to be safe, lighter weights should be used. You also can do dumbbell flyes using cables or resistance bands, or while lying on a stability ball, which helps work on balance and engages the abdominals.
— Gilliam is a personal trainer and fitness consultant.