Joint Angels

Joint angle (also called inter-segmental angle) is the simply the angle between two segments on either side of the joint, usually measured in degrees and often converted to mathematical notation. Since joint angles are relative to the segment angles, they don't change with the body orientation.

On the other hand segment angles are quite different. Segment angles are angles of the segment with respect to the right-hand horizontal. Segment angles are absolute measurements, that change according to the orientation of the body.

You can apply basic physics knowledge when finding joint angels. The use of velocity in movement has proven to be very useful. Velocity (distance moved / time taken ) is another word for speed. Velocity may be linear (change in position) measured in meters per second (m/s or ms-1), or angular (change in angle), measured in degrees per second (deg./s or deg.s-1). Normally, velocity is derived from position or angle data by the process of differentiation. For example: If a knee moves from a horizontal position of 1.5 m to a position of 1.6 m in 1/50 of a second, it has a velocity of Velocity = (1.6 - 1.5) / (1/50) = 0.1 x 50 = 5 ms-1. Acceleration is also valuable when addressing Joint angles. Acceleration is the change in velocity. Again, it may be linear (change in linear velocity) measured in meters per second per second (m/s2 or ms-2), or angular (change in angular velocity), measured in degrees per second per second (deg./s2 or deg.s-2). Acceleration, too, is usually calculated from the position data by differentiating twice. It can also be measured directly by an instrument called an accelerometer.