Linear Kinetics Applications Stability, Postural Sway

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Linear KineticsApplications Stability,
Postural Sway Balance

• ESS 5306-001
• Lecture 9
• Reading Winter, Chapter 4

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Additional Concept for Moments

• Mechanical Stability
• The resistance of an object to disruptions of
  equilibrium (e.g., falling over).
• Equilibrium
• No linear or angular accelerations

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Types of Equilibrium
Stable
Unstable
Neutral
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Additional Concept for Torque

• Q What determines when an object will fall over?
• A Position of its COM relative to its base of
  support (BOS).
• Factors that Determine Mechanical Stability
• Weight of the body
• Height of COM relative to the BOS
• Horizontal position of the line of gravity
  relative to the limits of the base.

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Postural Sway and Balance

• Quiet Stance
• Dual support (i.e., 2 feet)
• Single support (i.e., 1-foot)
• Visual feedback manipulation
• Perturbed Stance
• Physical perturbation
• Visually induced perturbation
• Galvanic Stimulation induced sway
• Slips, Trips and Falls Studies
• Recovery
• Seated posture and balance
• Sit to Stand
• Dynamic Stability (tougher to define)
• COP trajectory or velocity patterns during
  stance phase of a movement (e.g. gait, foot
  contact)

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Some Balance (Sway) Parameters

• Stabilogram (AP vs. ML COP plot)
• Sway radius (Mean, Peak, RMS, SD, s)
• AP and ML Radius (Mean, Max, SD, RMS)
• Area Ellipse
• Sway Velocity (Acceleration, Jerk, Snap)
• Velocity profiles within the BOS
• SDA (Stabilogram Diffusion Analysis)
• Critical time, Diffusion Coefficient, Scaling
  Exponent (0ltHlt1)
• Junction is switch from open loop feedback to
  closed loop feedback (occurring at critical time,
  t)
• Persistence (H gt ½, Predictable) and
  Anti-persistence (H lt ½, Unpredictable)

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Stabilogram Diffusion AnalysisSDA

• Method of averaging the changes in COP
  displacement over an ever increasing number of
  data points.
• Comparison
• Critical time, Diffusion Coefficient, Scaling
  Exponent (0ltHlt1)
• Junction is switch from open loop feedback to
  closed loop feedback
• Persistence (Hgt½) and Anti-persistence (Hlt½)

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SDA
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Stabilogram
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Max Radius
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Max or Mean M-L Radius
Max or Mean A-P Radius
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Area Ellipse
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Sway Velocity ?cop / ?t
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COP within BOS Quiet Stance Trials
1 mo. post
Baseline
2-mo. post
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Inverted Pendulum Model (theory)

• Theory regarding stability and postural control
• Theory
• COM must remain within the base of support in
  order for stability to be maintained
• Idea behind theory
• Center of Mass (body) sways within base of
  support
• When COM approaches boundaries of BOS
• Center of Pressure chases the COM
• Migrates to catch the COM
• May travel outside of the BOS and rope in the COM
  redirecting it back toward the center of the BOS
• Basically like balancing a bat upright on your
  palm

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For next time

• Muscle Mechanics EMG
• Reading from Chapter 8
• Article Critiques due before Thanksgiving
• Literature review papers due before Dec 5