TI 2 Mod 3, Topic 1 – Balance and Postural Stability

Balance and postural stability

Keeping the center of mass over the base of support

Center of mass (COM)

The point of perfect weight equilibrium; the center of the body's mass

Base of support (BOS)

The contact area between the body and the surface supporting it

Center of gravity (COG)

The vertical projection of the center of mass to the ground

Limit of stability (LOS)

The breaking point at which a person has to move their base of support to avoid losing balance

Visual system (balance)

Tells us where our head is in space; can help improve postural stability when vestibular or proprioceptive input is inadequate

Vestibular system (balance)

Gives information about position and movement of head in relation to gravity

Somatosensory/proprioception system (balance)

Tells us information about joint position sense (whether joints are flexed or extended and if they are moving); primarily from muscle spindle receptors

Ankle strategy

Small motion occurring at ankle to keep COM over BOS; muscle activation from distal to proximal; used for small anterior/posterior perturbations

Hip strategy

Hips rapidly flex or extend to maintain balance; muscle activation from proximal to distal; used for large or rapid anterior/posterior perturbations

Stepping strategy

Taking a step forward or back; used when perturbation displaces COM beyond limits of stability

Suspension strategy

Quick lowering of COM by flexing knees (causing hip flexion and ankle dorsiflexion); used to maintain COM over BOS (e.g. surfing)

Weight shift strategy

Taking a step to the side; used for lateral perturbation

Perturbation

A deviation from a regular or normal position caused by an outside influence (e.g. being pushed or a bus suddenly moving)

A/P

Shorthand for anterior-posterior; also known as forward-back or sagittal plane motion

Balance during lifting (CNS estimation)

CNS estimates momentum needed to lift load based on previous experience; loss of balance occurs when estimate is wrong (load lighter or heavier than expected)

Key principles for balance interventions

Identify activity where balance deficit is present; identify structure/system contributing; start at challenging but achievable level

Ankle strategy muscle activation for anterior perturbation

Gastrocs fire then hamstrings then paraspinal musculature (distal to proximal)

Ankle strategy muscle activation for posterior perturbation

Muscles on anterior side of body fire from distal to proximal

Hip strategy muscle activation for anterior perturbation

Hips rapidly flex

Hip strategy muscle activation for posterior perturbation

Hips rapidly extend

Suspension strategy joint positions

Quick knee flexion; then hip flexion and ankle dorsiflexion

Weight shift strategy for lateral perturbation

If force from left side body will take a step to the right