Gait Analysis and Biomechanics
Chapter 12
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
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 SWINGSWING
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)
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 SWINGSWING
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
• 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.
• 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
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
Guessing Game
• Sagittal plane joint angle
• Graphed for one side from heelstrike to heelstrike
• Vertical line separates stance phase from swing phase
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 stationary– Tibia is rotating over the foot
• Third rocker: Forefoot dorsiflexion as heel rises (foot rocker)
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-limb support
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 if they are weak?
Adaptations
• What can be done to protect quads?– Reduce flexion moment• How?
– Affect moment arm– How?
» Affect vector direction» Affect joint center
Adaptations
• What can be done to protect quads?– Reduce flexion moment• Move knee center back• Move GRF direction forward
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 moment
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 compression on the hip
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 motion
• Ground reaction forces and joint moments improve understanding of normal and pathological gait