10.1 - angular position, angular displacement, in range of motion

angular kinematics

• rotation; degrees, radians, resolutions, etc.

• angle, angular displacement (ROM), angular velocity, angular acceleration

• human movement involves rotation of body segments

angular motion

• all points move through the same angular isplacement

• points farther from center move through larger “linear” displacement

axis and spoke

• axis = joint

• spokes = body segments

1 degree

1/360th rotation

1 radian

½pi of a complete rotation (1 rad = 57.3 degrees)

1 revolution

1 complete rotation

• don’t really talk about that, as most joints shouldn’t move 360+ degrees

vertex

• instantaneous center of rotation

• for a human joint is not fixed (not still), but we assume it is for measuring

  • the knee doesn’t just flex, the tibia glides forward to close the gap

angular position

• angle that a segment (limb) is relative to an arbitrary reference

• examples:

  • arm is roughly 0 degrees relative to the trunk in sagittal plane in anatomical position

  • arm is roughly 90 degrees relative to line parallel to the ground in the sagittal plane in anatomical position

arbitrary reference

sometimes a body segment, sometimes more about absolute (parallel to the ground)

absolute angle

• angle of a segment compared to an externally defined line (typically parallel to the ground)

• named after the segment whose movement we are measuring

• @ elbow = arm angle

relative (“joint”) angle

• included between two body segments

• named for the joint that is at the vertex of the angle

in frontal plane, most joint angles have a value of __

• 180 degrees

• exceptions: foot, shoulder

2 ways to measure joint agles

• assuming anatomical position = 0 degrees; deviating from that position (elbow is 12 degrees of flexion)

• goniometry - segments lined up with the goniometer, measuring like a protractor

  • in anatomical position, elbow angle is 180 degrees

forearm absolute angle

2 possible vertex: arm or wrist

angular displacement

• the change in absolute angular position experienced by a rotating line

• the angle between a line segment in its initial position and in its final position with the direction of rotation noted

• units are degrees (or rad, or rev)

• angular displacement: 70 degrees

active range of motion

• ROM moved through by the patient/client’s own muscle power

passive ROM

ROM moved through with assistance from a therapist or equipment

active assisted ROM

ROM moved through by the patient/client with assistance via a strap, wall, etc.

angular displacement vs position

• position of a joint says some important information, but displacement is more informative

• angular displacement of a joint angle is more commonly known as ROM