The term 'bulk up, as muscles' can be summarized by the crossword solution 'SCULPT, ' which is a six-letter word. Sculpting is the art of creating three-dimensional forms from materials such as stone, wood, or metal. It is also used to refer to the process of shaping and strengthening the body through exercise. In this context, it means to build muscle mass and strength by engaging in physical activities such as weightlifting and bodybuilding.