Motions are classified after the
anatomical planes they occur in, although movement is more often than not a combination of different motions occurring simultaneously in several planes. Motions can be split into categories relating to the nature of the joints involved:
- Gliding motions occur between flat surfaces, such as in the
intervertebral discs or between the
metacarpal bones of the hand.
- Angular motions occur over
synovial joints and causes them to either increase or decrease angles between bones.
- Rotational motions move a structure in a
rotational motion along a longitudinal axis, such as turning the head to look to either side.
Apart from this motions can also be divided into:
- Linear motions (or translatory motions), which move in a line between two points. Rectilinear motion is motion in a straight line between two points, whereas curvilinear motion is motion following a curved path.
- Angular motions (or rotary motions) occur when an object is around another object increasing or decreasing the angle. The different parts of the object do not move the same distance. Examples include a movement of the knee, where the lower leg changes angle compared to the femur, or movements of the ankle.
The study of movement is known as
kinesiology. A categoric list of movements of the human body and the muscles involved can be found at
list of movements of the human body.
The prefix hyper- is sometimes added to describe movement beyond the normal limits, such as in
hypermobility, hyperflexion or hyperextension. The
range of motion describes the total range of motion that a joint is able to do. For example, if a part of the body such as a joint is overstretched or "bent backwards" because of exaggerated extension motion, then it can be described as hyperextended. Hyperextension increases the stress on the
ligaments of a joint, and is not always because of a voluntary movement. It may be a result of accidents, falls, or other causes of trauma. It may also be used in surgery, such as in temporarily dislocating joints for surgical procedures.