The upper part of the trapezius muscle is the primary target of the shoulder shrug. The trapezius is a triangular muscle that makes up the upper back, running from the back of the neck and down along the spine, lying over the shoulder blades.
In general terms, sex refers to the biological differences between males and females, such as the genitalia and genetic differences. Gender is more difficult to define but can refer to the role of a male or female in society (gender role), or an individual's concept of themselves (gender identity).
One of the main differences regards gender identification. Gender, according to many experts, is a social rather than biological definition. The social structures regarding male and female roles are what define gender, rather than the anatomical and scientific definitions that define what sex a person is.