Three-dimensional analyses of gait initiation in a healthy, young population Drew Smith 1 and Del P....
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Transcript of Three-dimensional analyses of gait initiation in a healthy, young population Drew Smith 1 and Del P....
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