L17 - Gait Analysis: Healthy & Pathological

• The forces that cause motion:

  • A push or pull - disturbing objects from their inertial state (1st Law)
  • An object will remain rest until external force applied = inertia
  • Relative to mass
  • A net force accelerates an object (2nd Law)
  • F = m * a
  • Any force exerted is opposed by an equal & opposite force (3rd Law)
  • Every action has an equal & opposite reaction
• Force is measured in Newtons (N):

  • 1 N of force will accelerate a 1 kg object by 1 m/s every second
  • 1 N = kg m/s^2
• Force is a vector quantity

  • With magnitude & direction
• Free body diagram is a technique of visualising & simplifying a problem by constructing a diagram showing all the forces acting
• Ground Reaction Force (GFR) & Centre of Pressure (CoP):

  • Centre of Pressure (CoP) or
  • “ Location of the force average force vector of interest ”
  • “ Centre of pressure ” can be misleading as it's not a measure of pressure but a measure of the position & refers to the average pressure point beneath the foot or feet
• Ground Reaction Force (GFR) & Centre of Pressure (CoP):

  • Exerting force on floor from mass → equal & opposite of mass equal if stationary
  • Mass exerts force onto ground; F = m * g
  • F = force, m = mass, g = gravity
  • Can measure reaction of that force with a force plate = a tool to measure action not just reaction
• Ground Reaction Force (GFR) & Centre of Pressure (CoP):

  • If not moving force under each foot is the same & the CoM reaction force acting upwards from both/or mass centre
  • If want average of these forces = CoP, CoP = location of C or average or the force vector
  • Is standing still CoP = directly under CoM = average of 2 reaction forces – CoP
  • If walking/moving not necessarily under CoM, force of foot centres so in foot
• Phase Division of Gait:

  • One gait cycle = ground contact to next ground contact of same foot
  • Stance phase = ground contact to toe-off
  • Swing phase = toe-off to ground contact
  • Double stance in walking replaced by flight phase in running
• Ground Reaction Force Fluctuation During Gait:

  • GRF changes magnitude
  • Throughout the stance phase
  • Moves horizontally (forward) as stance progresses into propulsion
  • Also vertical
  • Moves with us
  • Change in CoP
• Ground Reaction Force Fluctuation During Gait:

  • Gait Objectives:

  1. Propel our bodies forward
  2. To do so efficiency, requiring minimal energy expenditure

  • Adapt a gait typically to minimise energy expenditure of body
  • By not moving CoM too much, keep CoM range to a minimum
• Ground Reaction Force Fluctuation During Gait:

  • Forces in motion
  • Downward/upward = vertical
  • Forward/backward = horizontal
  • Vt & Hz forces changing throughout stance phase
  • CoP slides along the foot as you walk/move (towards propulsion - CoP moves forward)
  • Throughout the stance phase change in magnitude & direction of force vector (CoP)
• Ground Reaction Force Fluctuation During Gait:

  • Gait Objectives:

  1. Propel our bodies forward
  2. To do so efficiently, requiring minimal energy expenditure