The deltoid muscle is the hinge of the upper limbs

The waist and abdomen are the hinge between the upper and lower limbs, but what is the hinge of the upper limbs? I think it's the deltoids. People with strong deltoid muscles will definitely have good upper limbs, because the front deltoid muscles determine the level of your chest (for bench press). The middle deltoid determines your shoulder width and overall shape, while the rear deltoid has always been one of the dividing points between professionals and amateurs. In addition, whether blood vessels can be seen in the deltoid muscles is also an intuitive reflection of a person's body fat.