Fly of chest with dumbbells on a bench decline

Move the arms through a controlled arc with a slight bend in the elbows. Open or close only as far as you can without forcing the front of the shoulder. Use a steady tempo: control the return phase in particular and avoid relying on momentum. Exhale through the hardest part and inhale as you recover the starting position.

Check that the movement stays stable in both directions and that the torso is not compensating. The goal is controlled loading of chest; match resistance and range to a intermediate level and never force a painful repetition. Make sure the bench is stable and that the shoulders, pelvis or feet do not shift during the set.