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Gait Analysis and Biomechanics

Chapter 12

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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

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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

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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)

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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

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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

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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.

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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

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Children

Children have shorter legs, so cadence isincreased

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 anexpected stride length of about 0.5 m

Velocity is roughly 1 stature/s, so a child 0.5 mtall will have an expected walking velocity ofabout 0.5 m/s

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Guessing Game

Sagittal plane joint angle

Graphed for one side from heelstrike toheelstrike

Vertical line separates stance phase fromswing phase

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Joint Kinematics: sample

Ankle

Plantarflexion

Dorsiflexion

Heelstrike Toe-off Heelstrike

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Joint Kinematics

Ankle

Plantarflexion

Dorsiflexion

Heelstrike Toe-off Heelstrike

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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)

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Knee

Extension

Flexion

Heelstrike Toe-off Heelstrike

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Hip

Extension

Flexion

Heelstrike Toe-off Heelstrike

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Sprinting looks quite different

Note femur parallel to ground

Note clearance

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Ground Reaction Force

(Newtons 3rd Law of motion)

Walking

Heel strike transient

Slow

Fast

Running

No double-limb support

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One key to understanding gait

Moments!

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External Moments

Hip

Knee

Ankle

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External Moments

Hip

Knee

Ankle

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External Moments

Hip

Knee

Ankle

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External Moments

Hip

Knee

Ankle

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External Moments

Hip

Knee

Ankle

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Key to Understanding Pathological Gait

MOMENTS!

Example: what if quadriceps is weak?

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Whats theexternal

moment on the

knee?

Flexor or

extensor?

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Model

What muscles must

resist an external knee

flexor moment?

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Resisting a moment

The knee extensors must resist an external

knee flexion moment

What are the knee extensors?

What if they are weak?

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Adaptations

What can be done to

protect quads?

Reduce flexion moment

How?

Affect moment arm

How?

Affect vector direction

Affect joint center

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Adaptations

What can be done to

protect quads?

Reduce flexion moment

Move knee center back

Move GRF direction forward

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Anterior Trunk Lean

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Other solutions

Knee hyperextension

Dynamic Limb Retraction

Hand on thigh

http://guardian.curtin.edu.au/cga/archives/29-6-97/frontal1.mov

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Applications of Net Moments

Related to walking

Frontal Plane

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Identify:

Direction of moment

about right hip when left

leg is off the ground

Muscles that must fire to

resist that moment

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Question

What happens if right abductors are weak?

Trendelenberg Sign

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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

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Weight on one

leglarge

moment

resisted by

abductors

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Summary

Walking and running are complex cyclicmotions that involve interaction of both limbsand large sagittal plane motion

Ground reaction forces and joint momentsimprove understanding of normal andpathological gait