Lecture 5 - Angular Kinematics 2

Angular Position

Refer’s to a body’s location relative to a spatial reference system; 1 angle

Angular Distance

Total of all angular changes measured following a body’s exact path; 2+ angles

Angular Displacement (θ)

Angle through which a body has rotated about an axis; θ = θ_f - θ_i; 2+ angles

Absolute/Segment Angle

Angle of inclination of a body segment relative to a fixed reference; describes orientation of a body segment in space; coordinate system at distal end point of segment; angle measured CCW from right horizontal

• tanθ_abs = (y_proximal - y_distal)/(x_proximal - x_distal)

Relative/Joint Angle

Angle between longitudinal axes of two body segments; describes amount of flexion/extension at the joint; doesn’t describe where they are oriented in space

• Calculated using Cosine Law

Relative angle between two segments calculated by…

subtracting the absolute angle of distal segment from proximal segment

• θ_relative = θ_{absolute proximal} - θ_{absolute distal}

Absolute angles are used to describe…

function of the joint

Winter’s Absolute Angles

• θ_hip = θ_{absolute thigh} - θ_{absolute trunk}

• θ_knee = θ_{absolute thigh} - θ_{absolute leg}

• θ_ankle = θ_{absolute leg} - θ_{absolute foot} + 90°

Meaning of Winter’s Hip Angle

• Positive → flexion

• Negative → extension

• 0 → neutral position

Meaning of Winter’s Knee Angle

• Always positive → flexion

• 0 → neutral

• Negative → hyperextension

Meaning of Winter’s Ankle Angle

• Positive → dorsiflexion

• Negative → plantar flexion