Three-dimensional analyses of gait initiation in a healthy, young population

Drew Smith1 and Del P. Wong2

1 Motion Analysis Research Center (MARC), Samuel Merritt University, Oakland CA, USA

2 Technological & Higher Education Institute (THEi), Hong Kong SAR, PRC

Outline

Dynamic stability

Brief review of gait initiation

Three-dimensional analyses of gait initiation in a healthy, young population: Introduction, Methods, Results, Discussion

Directions for future study

Dynamic stability

Inverted pendulum model Most of our mass is located high above a small

base of support Gravity acts to de-stabilize system

Only 1 position is not unstable Requires a dynamic stability control system

Sensory + motor + reflexes + mechanical Failure of control system = falls (Gait = ‘controlled falling’)

Dynamic stability

Definition: Refers to the ability of the human to recover from

perturbations while maintaining an upright posture over a stationary or moving base of support Perturbations can be internal (muscle forces) or

external (gravity, pushes, pulls, changes in friction) Posture is the alignment of the body segments with

respect to gravity Balance is the maintenance of posture

Dynamic stability

Spectrum of inverted pendulum activities: Sit-to-stand => quiet standing => walking =>

running => walking => quiet standing , and so forth Special aspects: turns, ramps, stairs, obstacles Each phase meets criteria of pendulum model What about the transitions?

E.g., in what ways does quiet standing resemble walking? At what point does quiet standing become walking? Walking become running? And so forth.

What can successful transitions tell us about unsuccessful ones? E.g., ‘freezing’ in Parkinson's disease, or falls in the

elderly while negotiating turns while walking

Gait initiation research

Gait initiation Complete after 1, 2, or 3 steps

Quiet standing => gait initiation Step 1:

Soleus (-) and tibialis anterior (+) activity COP moves backward Paradoxically, swing limb is initially loaded then

unloaded Swing limb lifted by hip flexors

Gait initiation research

Differing views on when completed Depend on which variable being considered: COM

velocity, acceleration, joint angle patterns, GRF

To date, no 3D studies have been conducted Steady-state gait and quiet standing are well-

studied

Pronounced change in energy states make energy a good variable to study

Three-dimensional analyses of gait initiation

Purpose Examine patterns of joint powers and patterns of

energy absorption and generation during the first 3 steps, defined as gait initiation

Compare sagittal and frontal planes powers and energies

Hypotheses Sagittal powers and energies will have little

contribution before and during the initial transfer of weight in the first step (STEP1)

Most of the energy in STEP1 will come from hip joint In successive steps (STEP2, STEP3), sagittal plane

energies will dominate

Three-dimensional analyses of gait initiation

Methods Subjects:

15 undergraduate students provided informed consent to participate Mean (± SD) mass: 74.0 (±16.7) kg, height: 1746.9

(±102.3)mm, BMI: 24.1 (±4.2)kg-m² Protocol:

Standing, feet shoulder-width apart on two force platforms for min of 5s

Initiate walking with left foot landing on 3rd force platform.

Continue walking for a minimum of 4m 5 trials per subject

Three-dimensional analyses of gait initiation

Model: 21-markers defining 11 segments 8-camera VICON MX system (100Hz) 3 Bertec force platforms (1,000Hz)

Data analysis: Joint and segment kinematics and kinetics

Inverse dynamics Time-normalised (0-100%) of 3 successive steps

using 6 gait events Identified from averaged subject data

Three-dimensional analyses of gait initiation

Three-dimensional analyses of gait initiation

Joint powers: Product of joint moment of force and joint angular velocity

Joint absorption and generation energies: Calculated by integrating joint powers using a trapezoidal

technique

Statistics 3x2x2 ANOVA to examine main and interaction effects of

step, plane, and joint on absorption and generation energy

Post hoc test with Bonferroni correction where appropriate Paired-sample t-tests used where there were 2 groups

Three-dimensional analyses of gait initiation

Sagittal Frontal

Three-dimensional analyses of gait initiation

Sagittal Frontal

Three-dimensional analyses of gait initiation

Sagittal Frontal

Three-dimensional analyses of gait initiation

Results

Three-dimensional analyses of gait initiation

Results

#s: compareacross STEPs

K,H: comparebetween joints

Three-dimensional analyses of gait initiation

Hip has smallest correlations, ankle has largest for both legs

Right knee (STEP2) is negatively correlated

Three-dimensional analyses of gait initiation

Discussion: Analysis supported hypotheses Correlations between planes:

STEP1 and STEP3 (left leg) – increasing + correlations from proximal to distal joints

STEP2 (right leg) – similar in magnitude but knee is – correlation Raises possibility of energy flow not just between

joints in the same plane but between planes within the same joint Increases potential of system to be even more

efficient than previously believed

Directions for future research

Gait termination: Reverse pattern of gait initiation?

More energy absorption is likely

‘Freezing’ in Parkinson’s disease: Most interventions have focused on sagittal plane

Frontal plane has significant energies in frontal plane in STEP1

Joint stiffness: Calculating joint stiffness as a time-series

How does this pattern change in each plane? Can this have clinical implications?

Dr Shirley RietdykPurdue UniversityACKNOWLEDGEMENT