KINETIC ANALYSIS OF GAIT INITIATION

KINETIC ANALYSIS OFGAIT INITIATION

D. Gordon E. Robertson, PhD, FCSB1

Richard Smith, PhD2

Nick O’Dwyer, PhD2

1Biomechanics Laboratory,

School of Human Kinetics,

University of Ottawa, Ottawa, Canada

2Biomechanics Laboratory,

School of Exercise and Sport Science,

University of Sydney, Sydney, Australia

Introduction

Gait initiation usually consists of the period between quiet stance and steady-state gait. In most cases, it takes only 2 steps to reach steady-state. The leg that lifts first will be called lead-leg; the other leg will be the trail-leg. There are many studies that have documented the paths of the centres of pressure, the motion patterns and EMGs but very few studies which have computed inverse dynamics or moment powers.

Purpose

To examine the patterns of the moments of force and their powers of the lower extremities during gait initiation.

To determine the sequence of events required to initiate gait from quiet stance.

To observe whether similar patterns occur with a variety of subjects.

Methods

• Seven subjects performed five trials starting with their right leg

• Started with each foot on a separate force plate and stepped “briskly” to two other force plates and then continued several steps onto the floor

• Video taped at 200 fps, forces sampled at 1000 Hz using a Motion Analysis, EVaRT system

• 42 markers tracked to make 13-segment, 3D model

• Inverse dynamics and powers computed by Visual3D

Initiation of Gait: Events

Quiet stanceQuiet stance First toe-off(lead-leg)

First toe-off(lead-leg)

Second toe-off(trail-leg)

Second toe-off(trail-leg)

Results

• movements started approximately 1 to 1.5 seconds before trail-leg toe-off

• greatest variability and least movement occurred in first 0.5 seconds (loading phase of lead, unloading of trail) called Phase 1

• after Phase 1, consistent patterns of moments and powers began

• Phase 2 ended at first toe-off (lead-leg TO)

• Phase 3 ended at second toe-off (trail-leg TO)

Results:Centres of Pressure

-0.1

0.0

0.1

0.2

0.3

-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

Distance (m)

step 1step 1

step 2step 2

leadlead

trailtrail

bothboth

line of gravityline of gravity

Notice that as the combined centre of pressure moves backwards and towards the lead-leg the line of gravity proceeds forwards and towards the trail-leg. The line of gravity is outside the base of support shortly after the lead-leg lifts.

Notice that as the combined centre of pressure moves backwards and towards the lead-leg the line of gravity proceeds forwards and towards the trail-leg. The line of gravity is outside the base of support shortly after the lead-leg lifts.

Results – flexion/extension

ankleankle kneeknee hiphip

ang.vel’sang.vel’s

momentsmoments

powerspowers

Results – flexion/extensionLead-leg (until 2nd TO)

nonzero ‘postural’ momentsat ankle and knee with highvariability before toe-off

nonzero ‘postural’ momentsat ankle and knee with highvariability before toe-off

1st toe-off1st toe-off

hip flexors act concentricallybefore toe-off and early swingto flex hip and swing lead-leg

hip flexors act concentricallybefore toe-off and early swingto flex hip and swing lead-leg

- small plantar flexor power burst at push-off- knee extensors do negative work until midswing

- small plantar flexor power burst at push-off- knee extensors do negative work until midswing

Results – flexion/extension Trail-leg (until 2nd TO)

2nd toe-off2nd toe-off

plantar flexors inactive untiljust before lead-leg FS whenconcentric work done for apush-off

plantar flexors inactive untiljust before lead-leg FS whenconcentric work done for apush-off

- knee extensors stiffen knee during midstance- knee flexors do positive work at push-off

- knee extensors stiffen knee during midstance- knee flexors do positive work at push-off

- hip flexors act eccentricallybefore toe-off- switch to concentric work to create swing of trail-leg

- hip flexors act eccentricallybefore toe-off- switch to concentric work to create swing of trail-leg

Results – flexion/extension Both Legs (until 2nd TO)

1st toe-off1st toe-off

moments andpowers normalizedto body mass

moments andpowers normalizedto body mass

trail-leg ankle plantar flexors major source of energytrail-leg ankle plantar flexors major source of energy

lead and trail-leg hip flexors used to swing legslead and trail-leg hip flexors used to swing legs

trail-leg knee flexors do positive work at push-offtrail-leg knee flexors do positive work at push-off

Results – abduction/adductionBoth Legs (until 2nd TO)

1st toe-off1st toe-off

AdductionAdduction

AbductionAbduction

lead-leg hip abductors activateto initiate lateral shift whiletrial-leg abductors release

lead-leg hip abductors activateto initiate lateral shift whiletrial-leg abductors release

trail-leg abductors begin just before lead-leg TO while lead-leg abductorsbecome silent

trail-leg abductors begin just before lead-leg TO while lead-leg abductorsbecome silent

Results – flexion/extension First Two Steps (1st to 3rd TO)

2nd toe-off2nd toe-off

after first step, patterns of moments and powers are almost the same as normal steady-state patterns

after first step, patterns of moments and powers are almost the same as normal steady-state patterns

Summary

Phase 1 (posterolateral shift of CofP):– highly variable period consisting of release

of lead- and trail-leg plantar flexor moments (gastrocnemius & soleus going silent and tibialis anterior activating)

– simultaneous hip abductor moment from lead-leg (probably by TFL & gluteus medius) and release of the trail-leg abductors

Phase 2 (lead-leg raise to 1st TO): – lead-leg hip flexors activate to lift thigh

– slight activity by plantar flexors of lead-leg

– trail-leg passive or isometric

Summary

Phase 3 (lead-leg swing and trail-leg pushes):– trail-leg plantar flexors act to push body forward,

largest burst of positive power

– hip abductors of trail-leg act to shift body’s CM towards midline and landing area of lead-leg

– knee flexors of trail-leg assist hip flexors to flex knee and hip

Phase 4 (trail-leg swing, start normal walking): – begin normal walking pattern with slightly higher

dorsiflexor and knee extensor activity in early stance of lead-leg

Thank You

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