KINETIC ANALYSISOF GAIT 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. Leg that lifts first will be called lead leg other leg is trail leg. There are many studies that have documented the paths of the centres of pressure, the motion patterns and EMGs but there have been 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 sequence of events required to initiate gait from quiet stance.

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

Methods

• Seven subjects, five trials starting with preferred leg, than five trials with other leg

• Started with each foot on a separate force plate and stepped to two other plates and then several steps onto floor (4 force plates)

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

• 42 markers to make 13-segment 3D model of body

• Inverse dynamics done by Visual3D

Initiation of Gait Events and Phases

Quiet stanceQuiet stance First (lead) toe-offEnd phase 2

First (lead) toe-offEnd phase 2

Third toe-offEnd phase 3Third toe-offEnd phase 3

Results

• movements started approximately 1.5 seconds before toe-off of trail leg (start of Phase 4)

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

• afterwards consistent patterns of moments and powers begin

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

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

ResultsCentres 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 c. 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 after the lead-leg lifts.

Notice that as the combined c. 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 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’ momentswith high variability before toe-off at ankle and knee

nonzero ‘postural’ momentswith high variability before toe-off at ankle and knee

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 relativelyinactive until just before TO- concentric work done atpush-off

- plantar flexors relativelyinactive until just before TO- concentric work done atpush-off

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

- knee extensors stiffen knee during midstance- knee extensors 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 energy- hip flexors mainly used to swing legs

- trail-leg ankle plantar flexors major source of energy- hip flexors mainly used to swing legs

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

1st toe-off1st toe-off

AdductionAdduction

AbductionAbduction

lead-leg hip abductorsinitiate lateral shift of CMlead-leg hip abductorsinitiate lateral shift of CM

trail-leg abductors begin as just before lead-leg TO and continue to shift CM back to midline

trail-leg abductors begin as just before lead-leg TO and continue to shift CM back to midline

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

Results – abduction/adduction First Two Steps (1st to 3rd TO)

AdductionAdduction

AbductionAbduction

2nd toe-off2nd toe-off

Conclusions

Phase 1 (posterolateral shift of CofP):– release of both plantar flexor moments (by

gastrocnemius & soleus going silent and tibialis anterior activating)

– simultaneous hip abductor moment from lead-leg (probably by TFL & gluteus medius)

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

lead-leg

– slight activity by plantar flexors of lead-leg

– trail-leg relatively inactive

– “falling phase”

Conclusions

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 lead-leg assist hip flexors to flex knee and hip

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

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

Thank You

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