Angular Kinematics of Human Movement Biomechanics and ergonomics

Objectives Define angular motion angular motion Tools for Measuring Body Angles Relative versus Absolute Angles Instant Center of Rotation

Angular motion Rotating body has axis of rotation every point in the body moves in circle around the axis of rotation

Observing the Angular Kinematics human movement involves rotation of one or more body segments around the joints at which they articulate. inferences of coordination of muscle activity producing the joint actions can be made

Observing the Angular Kinematics Clinicians, coaches, and teachers of physical activities routinely analyze human movement Based on observation of timing and range of motion Developmental stages of motor skills are based on analysis of angular kinematics

3 Stages of development in kicking

Angular Motion In angular motion, or rotational motion around an axis, the axis of rotation is a line, real or imaginary, oriented perpendicular to the plane in which the rotation occurs, like the axle for the wheels of a cart.

Angles An angle is formed by the intersection of two lines, two planes, or a line and a plane. 

Measuring Angles 1.Filmed images 2.Videotapes and films of human movement 3.Computer software

Types of Angles Two types 1.Absolute angle 2.Relative angle

Types of Angles Relative angle: Anatomical reference position Absolute angle: Horizontal reference Vertical reference

Relative angle Angle formed between the longitudinal axes of adjacent body segments Relative angles should consistently be measured on the same side of a given joint. The convention used for measuring relative joint angles is that in anatomical reference position, all joint angles are at 0 0.

Shoulder Flexion

Absolute angle Angular orientation of a body segment with respect to a fixed line of reference. Absolute angles should consistently be measured in the same direction form a single reference – either horizontal or vertical

Tools for Measuring Body Angles 1.Goniometer: One arm fixed to protractor at 0 0 Other arm free to rotate Center of goniometer over joint center Arms aligned over longitudinal axes Accuracy depends positioning of goniometer Place marks on the skin

2-Electrogoniometer (elgon) A goniometer with an electrical potentiometer at its vertex

3.Inclinometer: devices used for direct assessment of human body segment angles Usually gravitationally based

Instant Center of Rotation Instant Center: Precisely located center of rotation at a joint at a given instant in time 1)Roentgenograms (x rays) 2)Instrumented spatial linkage with pin fixation

The exact location of the instant center for a given joint may be determined through measurements taken from roentgenograms (x rays), which are usually taken at 10 0 intervals throughout the range of motion at the joint. An Instrumented spatial linkage involving intracortical pin fixation has been used to quantify relative linear and angular movements at the knee.

Example: The instant center at the knee shifts during angular movement due to accompanying linear displacements between the femur and the tibia in all three planes.