10. Dumbbell bench fly The faux pas Lowering your arms too far
The facts This mistake places major stress on your shoulders and rotator cuff, the delicate muscles that sit underneath the shoulders. Plus, it becomes difficult to press arms up and use the chest muscles effectively.

The fix Lie faceup on bench, knees bent and feet on edge. Hold a dumbbell in each hand, arms extended above mid-chest, in a slight arc, palms in. Contract abs and keep chin level. Maintaining elbow arc, lower elbows down and out to the side until they are even with or slightly below shoulders. Press dumbbells up and in to starting position, without letting them touch or allowing shoulder blades to rise off the bench. Strengthens chest and front shoulders.