Biomechanics of Postural Control

Posture

• the orientation, or alignment, of the human body, and can be either static or dynamic

Ideal upright posture

• position in which all the body systems are aligned relatively vertically, and the LOG passes through or as close to the joint axis as possible

• frees up upper appendages and increases heigh

• has greater stress on spine and lower extremities, lower stability, and harder to circulate blood

Static Posture

• quiet stance

• body and its segments are distributed in a manner that maintains the body in equilibrium

Dynamic Posture

• perturbed stance

• postures in which the body or its segments are moving

Postural Control

• act of maintaining balance at rest, during movement, or with positional changes given the constraints of the individual, environments, or task

• involves orientation/posture and stability/balance

orientation/posture

• ability to maintain an appropriate relationship between the body and body segments for a particular task

stability/balance

• ability to control or maintain the center of gravity/mass within the base of support

reactive postural control

• happens as a response to external forces acting on the body

proactive postural control

• happens when the body readies itself in anticipation of upcoming movements

adaptive postural control

• adaptations occur in the sensory and motor systems in response to the task and environmental demands

T12

• level of center of gravity of children

S2

• level of center of gravity of adults

Stability

• dependent on

  • size of the base of support

  • height of the center of gravity

  • location of the gravity line

  • weight of the body

Postural sway

• motion of an upright body that is characterized by constant, minute displacements and corrections to maintain the center of mass over the body’s base of support

• primarily occurs at the ankle-foot segment

• increases in the elderly which relates to the incidence of falls

12°

• if a person is standing with a 4-in distance in between the feet, the sway in the sagittal plane is __

16°

• if a person is standing with a 4-in distance in between the feet, the sway in the coronal plane is __

Limit of Stability

• maximum distance that an individual is able to lean in any direction without loss of balance or without changing in the base of support

Ankle strategy

• most common automatic adjustment to anterior-posterior sway

• head and body movement as a unit over the feet with minimal hip and knee movement

• preferred when the challenge is small, slow and remains near the body’s midline

Hip Strategy

• control of posture that comes from the hip, pelvis, and trunk

• preferred when the postural challenge is large, fast, or if the support surface is too small to accommodate the ankle forces

Stepping or Reaching Strategy

• used for very large or very fast changes and result in realignment of the center of mass within the base of support

• uses stepping, hopping, or reaching in the direction of change

Ground Reaction Force

• equal and opposing force when the body comes in contact within the ground

• produced by the ground during stance phase or during gait

line of gravity

• direction of gravity is always going to be vertically downward pull from the center of mass toward the center of the earth

• stable when this runs through the center of its base of support

moment

• the tendency to cause a body to rotate about a specific point or axis

external moment

• rotational tendency created when the line of gravity passes at a distance from the joint axis

Internal Moment

• muscle contraction or passive tissue tension that counterbalances the external moment

Anterior

• position of the LOG in relation to the AO joint

Through

• position of the LOG in relation to the cervical joint

Anterior

• position of the LOG in relation to the Thoracic joint

Through

• position of the LOG in relation to the Lumbar joint

Posterior

• position of the LOG in relation to the Hip joint

Anterior

• position of the LOG in relation to the Knee joint

Anterior

• position of the LOG in relation to the Ankle joint

Flexion

• external moment of the AO Joint

• Flexion

• external moment of the Thoracic Joint

Extension

• external moment of the Hip Joint

Extension

• external moment of the Knee Joint

Dorsiflexion

• external moment of the Ankle Joint