Fall ‘11
Introduction to Biomechanics
Lab 3 – Introduction to Angular Kinematics
Page 1 of 6
Lab # 3  Angular Kinematics
Purpose:
The objective of this lab is to understand the relationship between segment angles and joint angles. Upon completion
of this lab you will:
•
Understand and know how to calculate absolute and relative angles.
•
Be able to generate angleangle diagrams from experimental data.
Introduction:
Angular kinematics refers to the kinematic analysis of angular motion. Angular motion occurs when all parts of an
object move through the same angle but do not undergo the same linear displacement. The object rotates around an
axis of rotation that is a line perpendicular to the plane in which the rotation occurs. Examples of angular motion are
the motion of a bicycle crank as you peddle across campus and the motion of your thigh around your hip joint as you
walk to class.
An understanding of angular motion is critical to comprehend how we move. Nearly all human movement involves
the rotation of body segments. The segments rotate about the joint centers that form the axis of rotation for these
segments. When an individual moves, the segments generally undergo both rotation and translation. Angular motion
of anatomical joints also reflects changes in length of muscles crossing the joint.
The relationships discussed for linear kinematics are comparable to those in angular kinematics:
Angular kinematic variables:
Angular position (
θ
)
= the angle of a segment or joint, measured in radians or degrees.
Angular displacement (
Δθ
)
= the difference between the initial and final angular positions
of the rotating object
(
Δθ
=
θ
final

θ
initial
)
Angular velocity (
ϖ
)
= change in angular position over a period of time (d
θ
/dt)
Angular acceleration (
α
)
= change in angular velocity over a period of time (d
ω
/dt)
Measuring Angles
:
An angle is composed of two lines that intersect at a point called the
vertex
. In a biomechanical analysis, the
intersecting lines are generally body segments and the vertex is their common joint. If you consider the longitudinal
axis of the shank segment as one side of an angle and the longitudinal axis of the thigh segment as the other side, the
vertex would be the joint center of the knee.
Angles can be determined from the coordinate points you generated in the previous lab. Coordinates of the joint
centers determine the sides and the vertex of the angle. For example, an angle at the knee can be constructed using
the thigh and shank segments. The coordinates of the ankle and knee joint centers define the shank segment, while
the coordinate of the hip and knee joint centers define the thigh segment. The vertex of the angle is the knee joint
center.
Angular measurements are presented in
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 '10
 McNittGray
 Angles, Trunk Angle Trunk Angle

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