12 human walking (1)
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1. Gait analysis involves defining the gait cycle, examining joint kinematics and ground reaction forces during walking and running. 2. Key events in the gait cycle include initial contact, toe-off, and opposite initial contact. Gait is characterized by stance and swing phases for each leg. 3. Understanding external joint moments is important for analyzing normal and pathological gait, as weak muscles may not be able to resist abnormal moments. Adapting walking patterns can reduce damaging joint moments in conditions like quadriceps weakness.
12 human walking (1)
- 1. Gait Analysis and Biomechanics Chapter 12
- 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. 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. 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. 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. 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. 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.
- 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. 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. Guessing Game Sagittal plane joint angle Graphed for one side from heelstrike to heelstrike Vertical line separates stance phase from swing phase
- 11. Joint Kinematics: sample Ankle Plantarflexion Dorsiflexion Heelstrike Toe-off Heelstrike
- 12. Joint Kinematics Ankle Plantarflexion Dorsiflexion Heelstrike Toe-off Heelstrike
- 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)
- 16. Sprinting looks quite different Note femur parallel to ground Note clearance
- 17. Ground Reaction Force (Newtons 3rd Law of motion) Walking Heel strike transient Slow Fast Running No double-limb support
- 18. One key to understanding gait Moments!
- 19. External Moments Hip Knee Ankle
- 20. External Moments Hip Knee Ankle
- 21. External Moments Hip Knee Ankle
- 22. External Moments Hip Knee Ankle
- 23. External Moments Hip Knee Ankle
- 24. Key to Understanding Pathological Gait MOMENTS! Example: what if quadriceps is weak?
- 25. Whats the external moment on the knee? Flexor or extensor?
- 26. Model What muscles must resist an external knee flexor moment?
- 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. Adaptations What can be done to protect quads? Reduce flexion moment How? Affect moment arm How? 損 Affect vector direction 損 Affect joint center
- 29. Adaptations What can be done to protect quads? Reduce flexion moment Move knee center back Move GRF direction forward
- 31. Other solutions Knee hyperextension Dynamic Limb Retraction Hand on thigh
- 32. Applications of Net Moments Related to walking Frontal Plane
- 33. Identify: Direction of moment about right hip when left leg is off the ground Muscles that must fire to resist that moment
- 34. Question What happens if right abductors are weak? Trendelenberg Sign
- 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
- 37. Weight on one leg large moment resisted by abductors
- 38. 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