ABSTRACT
In many examples within biomechanics it is important that we understand the movement of the body through both two-dimensional (width and height or x and y directions) and three-dimensional space (width, height and depth or more
of this movement it is therefore necessary to be able to define the space in which we are moving. Again, a number of descriptors are helpful in our understanding of movement in this space and these can be summarized as follows: the term origin refers to the point that is the start/beginning and it can also be classified as a reference point to which other movements are relative. In the case of a twodimensional (2D) plane or movement the origin is often the intersection point of the x and y axes (i.e., where the horizontal (x) and vertical (y) axes cross). This would be the reference point that has the coordinates of 0, 0 (x and y coordinates). In anatomical terms this point of origin is often referred to as the point of insertion for muscle, tendon or ligament. The word coordinates refers to the set of numbers (two numbers in a two-dimensional space and three numbers in a threedimensional space) that describe a point of location. The term plane refers to a flat two-dimensional surface and an axis refers to a straight line that often passes through a body, part or segment and is usually used to describe rotation. In this context it is important to clarify that the axis does not necessarily have to pass through the body or segment and it can be located elsewhere. Translate or translation is the word that can be used to mean the change in position of body parts or segments without rotation (as in the case of translatory motion along a straight line in a single plane). In anatomical terms this is often referred to as a drawer of a structure or joint. For example, an anterior drawer of your tibia would be to translate the bone (lower leg) in an anterior direction in a straight line. Rotate or rotation means to move the limb or segment through an angle about a joint or axis or rotation (movement of your lower leg about your knee joint would be an act of rotation). Vertical defines the upward direction or in the case of a flat two-dimensional surface it would be the y direction (upward), and horizontal defines the direction that is along the x axis (again with reference to a two-dimensional surface).
