Anatomical planes and axes are standardized, imaginary reference systems used by anatomists, physical therapists, and fitness professionals to describe human movement and body structure location. This common framework provides a universal language for clear and consistent communication about how the body moves in three-dimensional space.
Understanding the Three Anatomical Planes
An anatomical plane is an imaginary flat surface that passes through the body, dividing it into sections. These planes help classify the direction of joint or limb movement. The Sagittal Plane is the most commonly referenced plane.
The Sagittal Plane is a vertical divider that runs from front to back, splitting the body into left and right halves. If this plane passes directly through the body’s midline, dividing it into equal halves, it is called the midsagittal plane. Movements within this plane are generally forward and backward motions.
The other two cardinal planes are the Frontal and Transverse planes. The Frontal, or Coronal, Plane is a vertical divider that runs perpendicular to the sagittal plane, splitting the body into anterior (front) and posterior (back) sections. The Transverse, or Horizontal, Plane is a horizontal divider that separates the body into superior (upper) and inferior (lower) halves.
The Three Axes of Rotation
While planes describe the surface of movement, an axis of rotation is an imaginary straight line around which the movement pivots. Every movement occurs within a specific plane and rotates around an axis that is perpendicular to that plane. This perpendicular relationship is a fundamental concept in biomechanics.
The three primary axes correspond directly to the three anatomical planes. The Mediolateral Axis (or Transverse Axis) passes horizontally from side to side. It runs perpendicular to the Sagittal Plane, acting as the pivot point for all forward and backward movements.
The Anteroposterior Axis (or Sagittal Axis) runs horizontally from front to back. This axis is perpendicular to the Frontal Plane and serves as the rotation point for side-to-side motions. The Vertical or Longitudinal Axis runs vertically from top to bottom. It is perpendicular to the Transverse Plane and facilitates rotational movements.
Movement in the Sagittal Plane is defined by the Mediolateral Axis. When a joint moves forward or backward within the sagittal plane, the rotation occurs around the axis that pierces the body from side to side.
Movement Examples in the Sagittal Plane
Movements within the Sagittal Plane are characterized by Flexion and Extension, which are rotations occurring about the Mediolateral Axis. Flexion involves decreasing the angle between two body parts (e.g., bending the elbow or knee). Extension involves increasing that angle (e.g., straightening the elbow or hip).
Common activities confined to this plane include walking and running, where the hips and knees repeatedly flex and extend. Strength training exercises like the squat and the bicep curl are examples of sagittal plane movement. In the squat, the hip, knee, and ankle joints all flex and extend as the body lowers and rises.
Performing a forward lunge also demonstrates this principle, as the joints pivot on the mediolateral line to drive the body forward and back.