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 it’s
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)

14. Knee
Extension
Flexion
Heelstrike Toe-off Heelstrike

15. Hip
Extension
Flexion
Heelstrike Toe-off Heelstrike

16. Sprinting looks quite different
• Note femur parallel to ground
• Note clearance

17. Ground Reaction Force
• (Newton’s 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. What’s 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?
» Affect vector direction
» Affect joint center

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

30. Anterior Trunk Lean

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