Kinetics in Gait

• Ground reaction force:

  • Newtons 3rd law of motion - equal and opposing forces
  • as the bodies weight exerts a force onto the ground, the ground will exert an equal and opposing force onto the body
  • forces are vectors therefore the ground reaction force will have a direction and magnitude
• Ground reaction force during gait:

  • during initial heel contact, GRF is vertical from the heel
  • after this the GRF passes through the centre of the knee joint and hip joint - this means theres minimal rotational force around these joints (the further the GRF is from a joint, the more rotational force there is)
  • as stance phase progresses the GRF continues to pass around the centre of the knee and hip joints
  • at the end of stance phase the GRF moves behind the knee, creating a rotational force of flexion at the knee

  
• The most amount of GRF occurs at the beginning of stance phase and at push off as that is when the knee is dealing with the most force

  
• Abnormalities in GRF:

  • patients could be using their GRF to assist their walking
  • by leaning forward, pressure is also brought forward on the foot, so GRF is further than it usually is, so passes in front of the knee joint, creating an extension force at the knee - used by patients with weak quadriceps

  
• Abnormalities in GRF:

  • some patients walk without their heel touching the ground
  • GRF acts on the front of the foot, passing in front of the knee, creating an extension force - used by patients with weak quadriceps

  
• Abnormalities in GRF:

  • some patients may walk whilst leaning back, bringing GRF to the back of the heel, passing behind the hip to assist with hip extension