kinetic analysis of gait initiation
DESCRIPTION
KINETIC ANALYSIS OF GAIT INITIATION. D. Gordon E. Robertson, PhD, FCSB 1 Richard Smith, PhD 2 Nick O’Dwyer, PhD 2 1 Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Canada 2 Biomechanics Laboratory, School of Exercise and Sport Science, - PowerPoint PPT PresentationTRANSCRIPT
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
• Any questions?
• Comments?