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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