Kinematics is the study of motion without regard to its causes – it is the motion of a rigid body within a defined reference system – can be translation which occurs when all particles within the rigid body undergo an equal linear displacement with a specified time period or it can be rotation which occurs when all particles within the rigid body move in a circular path about the same centre. Motion can take three forms – translation, rotation or a combination of the translation and rotation.

Osteokinematics – describes motion of bone relative to the three body planes.
Arthrokinematics – describes the motion that occurs between the articular surfaces of joints

Kinematic Data

Biomechanics labs use …

Reference systems:
Need a spatial reference system – most laboratories use a Cartesian co-ordinate system – can be 2 or 3 dimensional.

Linear kinematics

• in mechanics, ‘distance’ is the length of a path travelled by a body
• scalar quantity

• the straight line that connects a point’s position from one instant in time to another
• how far a body has moved from a starting point
• vector quantities (has magnitude and direction)

• the rate of change of distance over time
• scalar quantity (no direction)
• average speed = distance/time

• the rate of change of displacement
• vector quantity (as displacement is a vector)
• average velocity = change in displacement/duration of time

• rate of change of velocity
• also, rate of change of rate of change of displacement
• vector quantity
• often difficult to grasp concept, but fundamental to understanding kinematics

Angular/rotational kinematics

Uses same concepts as linear kinematics, but applies them to a body rotating about an axis.

Angular Displacement:
• defined as the changes in angular position
• angular quantities measured in radians (rad) – a rad is the angle formed by a arc length on a circle equal to the radius of the circle

Angular velocity:
• the rate of change if angular displacement (radians per second)
• can be calculated as the average angular velocity or the instantaneous angular velocity

Angular acceleration:
• the rate of change of angular velocity (radians/second2)
• can be calculated average angular acceleration or instantaneous angular acceleration

Instant centre of rotation (ICR):

Joint axes of rotation:
Bones rotate about a joint in a plane that is perpendicular to an axis of rotation.

Degrees of freedom:
The number of independent movements allowed at a joint – a joint can have up to 3 degrees of freedom.

Screw/Helical axis:
In 3 dimensional analysis instead of using an ICR, the concept of a screw or helical axis is used – that is that any rigid body’s motion may be described as a combination of rotation about an axis and translation along that same axis.

Projectile Motion:
The motion of a body under the influence of gravity only

Measurement of Gait Kinematics:



2D Kinematics:
Limitations of 2D:
• Parallax error
• Perspective error

3D Gait Analysis:

The modified Helen Hayes model

We have not yet got to this page. We will eventually. Please contact us if you have something to contribute to it or sign up for our newsletter or like us on Facebook and Instagram or follow us on Twitter.

Page last updated: @ 2:18 am

Comments are closed.