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KINETIC ANALYSIS OF GAIT INITIATION

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,

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KINETIC ANALYSIS OF GAIT INITIATION

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  1. 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

  2. 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.

  3. Purpose To examine the patterns of the moments offorce 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.

  4. 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

  5. Initiation of Gait:Events Quiet stance First toe-off (lead-leg) Second toe-off (trail-leg)

  6. 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)

  7. trail line of gravity step 2 both 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. lead step 1 Results:Centres of Pressure

  8. ankle knee hip moments ang.vel’s powers Results – flexion/extension

  9. nonzero ‘postural’ moments at ankle and knee with high variability before toe-off - small plantar flexor power burst at push-off - knee extensors do negative work until midswing hip flexors act concentrically before toe-off and early swing to flex hip and swing lead-leg 1st toe-off Results – flexion/extensionLead-leg (until 2nd TO)

  10. plantar flexors inactive until just before lead-leg FS when concentric work done for a push-off - knee extensors stiffen knee during midstance - knee flexors do positive work at push-off • - hip flexors act eccentrically • before toe-off • switch to concentric work to • create swing of trail-leg 2nd toe-off Results – flexion/extension Trail-leg (until 2nd TO)

  11. trail-leg ankle plantar flexors major source of energy trail-leg knee flexors do positive work at push-off lead and trail-leg hip flexors used to swing legs moments and powers normalized to body mass 1st toe-off Results – flexion/extension BothLegs (until 2nd TO)

  12. lead-leg hip abductors activate to initiate lateral shift while trial-leg abductors release trail-leg abductors begin just before lead-leg TO while lead-leg abductors become silent 1st toe-off Results – abduction/adductionBothLegs (until 2nd TO) Adduction Abduction

  13. after first step, patterns of moments and powers are almost the same as normal steady-state patterns 2nd toe-off Results – flexion/extension First Two Steps (1st to 3rd TO)

  14. 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

  15. 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

  16. Thank You • Any questions? • Comments?

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