When you exercise, you will find that most of the methods of training the pectoral muscles are actually training the deltoid muscles of the biceps brachii, because the force is exerted on the arms and shoulders, and the movements and movements of the pectoral muscles are often accompanied by the movements of the hands, so the shoulders are often sore during training, because the pectoral muscles can basically be understood as static when they are not moving, which is a normal phenomenon.