1. Dumbbell is a biaxial instrument, which is more flexible. Lifting dumbbells requires more auxiliary muscles to stabilize them, so it is difficult to push dumbbells on the bench. Dumbbells, because of their flexibility, can make elbows deeper, chest muscles stretch longer, do more work, shape and stretch chest muscles, and enhance the strength of auxiliary muscles. Moreover, biaxial instruments can make the strength more balanced, which can be used to balance the development of muscle strength and improve the weak side. 2. Using barbell can put a lot of weight, because it limits the stretching distance of the arm, and large weight generally means greater stimulation to the muscles. So generally speaking, barbell bench press is to use large weight to increase the strength or thickness of chest muscles.