Posture

• POSTURE


  Can either be STATIC or DYNAMIC
• Static Posture


  the body and its segments are aligned and maintained in certain a certain position
• Examples of Static POsture


  • standing, sitting, lying, and kneeling
• Dynamic POsture


  the body or its segments are

  moving
• Examples of Dynamic Posture

  walking, running, jumping, throwing, and

  lifting.
• Base of Support


  an area bounded posteriorly by the tips of the heels and anteriorly by a line joining the tips of the toes.
• Standing BoS is lesser then Quadrupedal BoS
• Center of gravity (CoG) or Center of mass (CoM)


  the point where the mass of the body is centered.

  Its position is not fixed
• Center of gravity (CoG) or Center of mass (CoM)

  • Young child - ~ level of the 12th vertebra

  • Normal standing adult - ~ anterior S2

  • Sitting position - armpits
• Standing erect = Small BoS, High CoM ->unstable
• Postural Control


  • refers to a person’s ability to maintain stability of the body and body segments in response to forces that threaten to disturb the body’s equilibrium
• Postural Control 


  Can be either static or dynamic
• Central Nervous System (CNS)


  Responsible for maintaining stability during erect standing posture
• Reactive or Compensatory response


  Occurs as reactions to external forces that displace the body's CoM
• Proactive or Anticipatory response


  Occurs in anticipation of internally generated destabilizing forces
• Goals of Postural Control

  • Control the body's orientation in space
  • Maintain the body's CoM over the BoS
  • Stabilize the head with regard to the vertical
• Primary goal of Postural Control

  • Stabilize the head with regard to the vertical
• Absent or Altered Inputs and Outputs


  may result to altered posture and compromised

  stability
• Alteration or Absence of Inputs

  • The absence of the normal gravitational force in weightless conditions during space flight
  • Decreased sensation in the lower extremities
• Altered outputs


  The inability of the muscles to respond appropriately to signals from the central nervous system
• Altered outputs

  • Difficulty in maintaining an erect position
• Perturbation


  Any sudden change in conditions that displaces the body posture away from equilibrium
• Sensory perturbation


  Altering the visual input, ex. covering a person's eyes
• Mechanical perturbation


  Directly changing the relationship of the body's CoM to the BoS
• Mechanical perturbation

  1. Moving a body segment

  2. Moving the entire body
• Mechanical perturbation


  • Breathing
• Factors that affect synergies

  • Amount and direction of motion of the supporting surface
  • Width and compliance of the supporting surface
  • Location, magnitude, and velocity of the perturbing force
  • Initial posture of the individual at the time of the perturbation
• Fixed-Support Synergies


  the BoS remains fixed during the perturbation and recovery. Stability is regained through moving your body while the feet remain fixed on the ground
• 2 strategies of FIxed-Support Synergies

  • Ankle Fixed

  • Hip synergy
• Ankle Synergy


  consists of discrete bursts of muscle activity on a

  distal-to-proximal pattern in response to forward

  or backward movements of a support platform
• Ankle Synergy

  Usually for perturbations that are slow and of low

  amplitude
• Ankle Synergy

  Forward motion of the platform -> posterior

  displacement of the line of gravity (LoG).

  Muscles activated= ankle dorsiflexors, hip flexors,

  abdominal muscles, and possibly the neck flexors
• Ankle Synergy

  Backward motion of the platform -> anterior

  displacement of the LoG.

  Muscles activated=plantarflexors, hip extensors, trunk extensors, and neck extensors
• Hip Synergy


  consists of discrete bursts of muscle activity in a

  proximal-to-distal pattern of activation opposite to

  the ankle synergy
• Hip Synergy

  Used when perturbations are fast or of large

  amplitude
• Hip Synergy


  May be used primarily when change-in-support

  strategies are not possible
• Change-In Support Strategies


  include stepping forward, backward, or sidewise

  and grasping like using one’s hands to grab a bar or other

  fixed support, in response to shifts in either the BoS or the

  entire body like with the tether release system.
• Change-in Support Strategies

  Stepping/grasping either moves or enlarges the body’s BoS to maintain it under the body’s CoM
• stepping strategy

  common in the young and old:

  Young ->only 1 step

  old->multiple shorter steps
• Stepping Strategy

  For large perturbation