Gait Analysis and Biomechanics
Chapter 12
Overview
• Defining the gait cycle
• Guessing game: sagittal joint kinematics
• Sprinting kinematics
• Ground reaction for...
Basic Vocabulary
• The gait cycle: initial contact of one leg to
initial contact of the same leg
– E.G. right heelstrike ...
Basic Vocabulary
• Includes important events:
– Initial contact (heelstrike)
– Toe-off
– Opposite toe-off (e.g. when the l...
Basic Vocabulary
• Base of support
– At heelstrike, you are in double limb support
– In the middle of stance phase, you ar...
Cadence and Step Length
• Step Length
– distance from one foot strike to the next (left to
right or right to left)
– about...
• Cadence
– number of steps (left and right) taken per minute
– about 110 st/min for normal adults
– Like a pendulum, lowe...
• Velocity
– about 1.5 m/s or 5 km/hr in normal adults
• Velocity = stride length x cadence
120
• and therefore:
• Stride ...
Children
• Children have shorter legs, so cadence is
increased
– 170 st/min at age 1 yr to 140 st/min at 7y
• Stride lengt...
Guessing Game
• Sagittal plane joint angle
• Graphed for one side from heelstrike to
heelstrike
• Vertical line separates ...
Joint Kinematics: sample
• Ankle
Plantarflexion
Dorsiflexion
Heelstrike Toe-off Heelstrike
Joint Kinematics
• Ankle
Plantarflexion
Dorsiflexion
Heelstrike Toe-off Heelstrike
Ankle Rockers (Perry)
• First rocker: ankle platarflexion after
heelstrike
• Second Rocker: ankle dorsiflexion
– Foot is s...
Knee
Extension
Flexion
Heelstrike Toe-off Heelstrike
Hip
Extension
Flexion
Heelstrike Toe-off Heelstrike
Sprinting looks quite different
• Note femur parallel to ground
• Note clearance
Ground Reaction Force
• (Newton’s 3rd
Law of motion)
• Walking
– Heel strike transient
– Slow
– Fast
• Running
– No double...
One key to understanding gait
• Moments!
External Moments
• Hip
• Knee
• Ankle
External Moments
• Hip
• Knee
• Ankle
External Moments
• Hip
• Knee
• Ankle
External Moments
• Hip
• Knee
• Ankle
External Moments
• Hip
• Knee
• Ankle
Key to Understanding Pathological
Gait
• MOMENTS!
• Example: what if quadriceps is weak?
What’s the
external
moment on the
knee?
Flexor or
extensor?
Model
• What muscles must
resist an external knee
flexor moment?
Resisting a moment
• The knee extensors must resist an external
knee flexion moment
• What are the knee extensors?
• What ...
Adaptations
• What can be done to
protect quads?
– Reduce flexion moment
• How?
– Affect moment arm
– How?
» Affect vector...
Adaptations
• What can be done to
protect quads?
– Reduce flexion moment
• Move knee center back
• Move GRF direction forw...
Anterior Trunk Lean
Other “solutions”
• Knee hyperextension
• Dynamic Limb Retraction
• Hand on thigh
Applications of Net Moments
• Related to walking
• Frontal Plane
• Identify:
– Direction of moment
about right hip when left
leg is off the ground
– Muscles that must fire to
resist that ...
Question
• What happens if right abductors are weak?
• Trendelenberg Sign
What could a cane do at the hip?
• Construct a free body diagram that
demonstrates how the use of a cane can
alleviate com...
Weight on one
leg – large
moment
resisted by
abductors
Summary
• Walking and running are complex cyclic
motions that involve interaction of both limbs
and large sagittal plane m...
12 human walking (1)
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12 human walking (1)

  1. 1. Gait Analysis and Biomechanics Chapter 12
  2. 2. 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
  3. 3. 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
  4. 4. 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)
  5. 5. 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
  6. 6. 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
  7. 7. • 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 it’s length, so shorter people have a higher cadence.
  8. 8. • 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
  9. 9. 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
  10. 10. Guessing Game • Sagittal plane joint angle • Graphed for one side from heelstrike to heelstrike • Vertical line separates stance phase from swing phase
  11. 11. Joint Kinematics: sample • Ankle Plantarflexion Dorsiflexion Heelstrike Toe-off Heelstrike
  12. 12. Joint Kinematics • Ankle Plantarflexion Dorsiflexion Heelstrike Toe-off Heelstrike
  13. 13. 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)
  14. 14. Knee Extension Flexion Heelstrike Toe-off Heelstrike
  15. 15. Hip Extension Flexion Heelstrike Toe-off Heelstrike
  16. 16. Sprinting looks quite different • Note femur parallel to ground • Note clearance
  17. 17. Ground Reaction Force • (Newton’s 3rd Law of motion) • Walking – Heel strike transient – Slow – Fast • Running – No double-limb support
  18. 18. One key to understanding gait • Moments!
  19. 19. External Moments • Hip • Knee • Ankle
  20. 20. External Moments • Hip • Knee • Ankle
  21. 21. External Moments • Hip • Knee • Ankle
  22. 22. External Moments • Hip • Knee • Ankle
  23. 23. External Moments • Hip • Knee • Ankle
  24. 24. Key to Understanding Pathological Gait • MOMENTS! • Example: what if quadriceps is weak?
  25. 25. What’s the external moment on the knee? Flexor or extensor?
  26. 26. Model • What muscles must resist an external knee flexor moment?
  27. 27. Resisting a moment • The knee extensors must resist an external knee flexion moment • What are the knee extensors? • What if they are weak?
  28. 28. Adaptations • What can be done to protect quads? – Reduce flexion moment • How? – Affect moment arm – How? » Affect vector direction » Affect joint center
  29. 29. Adaptations • What can be done to protect quads? – Reduce flexion moment • Move knee center back • Move GRF direction forward
  30. 30. Anterior Trunk Lean
  31. 31. Other “solutions” • Knee hyperextension • Dynamic Limb Retraction • Hand on thigh
  32. 32. Applications of Net Moments • Related to walking • Frontal Plane
  33. 33. • Identify: – Direction of moment about right hip when left leg is off the ground – Muscles that must fire to resist that moment
  34. 34. Question • What happens if right abductors are weak? • Trendelenberg Sign
  35. 35. 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
  36. 36. Weight on one leg – large moment resisted by abductors
  37. 37. 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
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