A fly is a strength training exercise in which the hand and arm move through an arc while the elbow is kept at a constant angle. The Chest Fly forces the chest to work to support the arm movement and thus opens the chest while strengthening these muscles we often ignore. 1. Lay on your back (or a balance ball as shown in the picture) with your arms and dumbbells raised straight above your head. 2. Bend your elbows slightly and lower your arms out and to the side. 3. Slowly bring your arms back to the starting position.