This document provides a reference system for analyzing human movement. It defines key anatomical concepts including the center of gravity, anatomical position, and standard standing position. It then describes three planes (frontal, sagittal, horizontal) and three axes (frontal, sagittal, vertical) that are used to analyze movement in relation to the body. The planes are two-dimensional surfaces that divide the body into halves, while the axes are imaginary lines that movements occur around.