Gait Analysis and Biomechanics

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Gait Analysis and Biomechanics

• Chapter 12

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Overview

• Defining the gait cycle
• Guessing game sagittal joint kinematics
• Sprinting kinematics
• Ground reaction forces
• Walking at different speeds
• Running
• Implications on Joint Moments
• One pathology

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Basic Vocabulary

• The gait cycle initial contact of one leg to
  initial contact of the same leg
• E.G. right heelstrike ? right heelstrike
• Includes two phases
• Stance Phase when the foot is on the ground
• Swing Phase when the leg is swinging forwards

SWING
SWING
SWING
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Basic Vocabulary

• Includes important events
• Initial contact (heelstrike)
• Toe-off
• Opposite toe-off (e.g. when the left leg leaves
  the ground)
• Opposite initial contact (e.g. when the left leg
  finishes swinging and hits the ground again)

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Basic Vocabulary

• Base of support
• At heelstrike, you are in double limb support
• In the middle of stance phase, you are in single
  limb support
• After opposite heelstrike, you are once again in
  double limb support

SWING
SWING
SWING
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Cadence and Step Length

• Step Length
• distance from one foot strike to the next (left
  to right or right to left)
• about 0.75 m for normal adults
• Stride Length (one gait cycle)
• two successive steps (by both left and right
  feet)
• about 1.5 m for normal adults

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• Cadence
• number of steps (left and right) taken per
  minute
• about 110 st/min for normal adults
• Like a pendulum, lower-limb swings at a frequency
  (cadence) inversely proportional to its length,
  so shorter people have a higher cadence.

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• Velocity
• about 1.5 m/s or 5 km/hr in normal adults
• Velocity stride length x cadence
• 120
• and therefore
•  
• Stride length 120 x velocity
• cadence

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Children

• Children have shorter legs, so cadence is
  increased
• 170 st/min at age 1 yr to 140 st/min at 7y
• Stride length is roughly the same as height
  (stature), so a child 0.5 m tall will have an
  expected stride length of about 0.5 m
• Velocity is roughly 1 stature/s, so a child 0.5 m
  tall will have an expected walking velocity of
  about 0.5 m/s

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Guessing Game

• Sagittal plane joint angle
• Graphed for one side from heelstrike to
  heelstrike
• Vertical line separates stance phase from swing
  phase

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Joint Kinematics sample

• Ankle

Dorsiflexion
Plantarflexion
Heelstrike
Heelstrike
Toe-off
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Joint Kinematics

• Ankle

Dorsiflexion
Plantarflexion
Heelstrike
Heelstrike
Toe-off
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Ankle Rockers (Perry)

• First rocker ankle platarflexion after
  heelstrike
• Second Rocker ankle dorsiflexion
• Foot is stationary
• Tibia is rotating over the foot
• Third rocker Forefoot dorsiflexion as heel rises
  (foot rocker)

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Knee
Flexion
Extension
Heelstrike
Heelstrike
Toe-off
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Hip
Flexion
Extension
Heelstrike
Heelstrike
Toe-off
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Sprinting looks quite different

• Note femur parallel to ground
• Note clearance

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Ground Reaction Force

• (Newtons 3rd Law of motion)
• Walking
• Heel strike transient
• Slow
• Fast
• Running
• No double-limb support

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One key to understanding gait

• Moments!

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External Moments

• Hip
• Knee
• Ankle

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External Moments

• Hip
• Knee
• Ankle

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External Moments

• Hip
• Knee
• Ankle

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External Moments

• Hip
• Knee
• Ankle

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External Moments

• Hip
• Knee
• Ankle

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Key to Understanding Pathological Gait

• MOMENTS!
• Example what if quadriceps is weak?

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Whats the external moment on the knee? Flexor
or extensor?
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Model

• What muscles must resist an external knee flexor
  moment?

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Resisting a moment

• The knee extensors must resist an external knee
  flexion moment
• What are the knee extensors?
• What if they are weak?

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Adaptations

• What can be done to protect quads?
• Reduce flexion moment
• How?
• Affect moment arm
• How?
• Affect vector direction
• Affect joint center

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Adaptations

• What can be done to protect quads?
• Reduce flexion moment
• Move knee center back
• Move GRF direction forward

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Anterior Trunk Lean
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Other solutions

• Knee hyperextension
• Dynamic Limb Retraction
• Hand on thigh

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Applications of Net Moments

• Related to walking
• Frontal Plane

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• Identify
• Direction of moment about right hip when left leg
  is off the ground
• Muscles that must fire to resist that moment

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Question

• What happens if right abductors are weak?
• Trendelenberg Sign

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What could a cane do at the hip?

• Construct a free body diagram that demonstrates
  how the use of a cane can alleviate compression
  on the hip

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Weight on one leg large moment resisted by
abductors
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Summary

• Walking and running are complex cyclic motions
  that involve interaction of both limbs and large
  sagittal plane motion
• Ground reaction forces and joint moments improve
  understanding of normal and pathological gait