GE 345: Week 8
Skeletal System
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[ Skeleton ]
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[ Articulations ]
[ Stability & Movement ]
This page covers basic terminology for describing human motion and anatomical positioning. For a more thorough description, try A Biomechanics-Based Model for the Animation of Human Locomotion, from the Department of Computer & Information Sciences, De Montfort University.
Anatomical/Kinesiological Terminology
- Center of Gravity (CG): imaginary point representing the weight center of an object, or the point in a body about which all parts balance each other. Depends on anatomical structure, standing posture, position, and support of external weights. On average, standing erect with arms at sides, the center of gravity is in the pelvis in front of the upper part of the sacrum. Usually lower in women.
- Line of Gravity: imaginary vertical line passing through the center of gravity.
- Orientation Planes: correspond to three dimensions of
space and axes of motion perpendicular to the plane in which motion occurs.
- Sagittal Plane (anteroposterior or median): passes through body front to back, dividing it into right and left halves.
- Frontal Plane (lateral or coronal): vertical plane passing left to right, dividing body into anterior and posterior halves.
- Transverse (horizontal): horizontal plane passing through the body, dividing it into upper and lower halves.
Each plane bisects the body and passes through the center of
gravity. The CG can be defined as the point where the three planes intersect.
The line of gravity is the vertical line at which the two vertical planes
intersect. Movements described in a particular plane typically occur in a
parallel plane.
- Axes of Motion: point around which rotary motion occurs. The axis is
perpendicular to the plane in which motion occurs
- Lateral (frontal-horizontal): passes horizontally side to side
- Anteroposterior (sagittal-horizontal): passes horizontall front to back.
- Vertical/Longitudinal: perpendicular to the ground
- Anatomical Standing Position: position usually depicted in anatomy texts. Individual stands with elbows extended and palms facing forward, feet slightly separated and parallel. Used as point of reference for joint movements.
Segmental Movement/Positioning
Sagittal plane about a lateral/right-left axis.
- Flexion: joint angle decreases, such as bending the knee or elbow. A bent elbow is flexed.
- Extension: return movement from flexion. Joing angle increases. Hyperextension is the continuation of extension beyond the straight line, such as extending the arm backward beyond the body. When your thigh is extended behind your body, it is said to be hyperextended.
Frontal plane about an anteroposterior axis.
- Abduction: sideward movement away from the mid-sagittal plane.
- Adduction: return movement from abduction.
Transverse plane about a vertical/longitudinal axis. Motions occuring would be rotation. Depending on the joint, rotation is described in the following ways...
- Left/Righ: applies to head or neck.
- Lateral/Outward: applies to rotation of extremities in such a way the segment turns laterally away from the midline when viewed from the front.
- Medial/Inward: rotation of extremities so the segment turns toward the body's midline when viewed from the front.
- Supination and Pronation: applies to outward (supination) and inward (pronation) rotation of the forearm.
Oblique planes and axes. Movements occuring somewhere between the defined planes, or are multi-planar, occur around oblique (or diagonal) axes. A diagonal movement would be raising the arm between the straight forward and straight sideward directions. A multiplanar movement that circumscribes a cone involves movements occuring in multiple planes, and is known as circumduction. Circling the arm is an example of circumduction.
[ Bone ]
[ Skeleton ]
[ Terms ]
[ Articulations ]
[ Stability & Movement ]