Postural Control

Postural Orientation Posture

ability to maintain an appropriate relationship

• between the body segments

• between the body and the environment for a task

Postural Stability - Balance

Ability to maintain the body in equilibrium at rest (static) or in steady state motion (dynamic)

Postural Adjustments

Muscle activation patterns and segmental movements that enable us to control the body’s segmental linkages in relation to the base of support

Postural Control

ability to do postural adjustments for the dual purpose of orientation and stability

(aside from Cortical function)

1. Vestibular System

2. Visual System

3. Somatosensory system

3 Major Systems Contributing to Postural Control:

balance

Postural Stability is synonymous with _______

center of mass is maintained over its base of support

Requirement for postural stability

• BOS

• COP

• Height

• Weight

• Velocity

Postural Stability - Limits of stability

Center of pressure

Postural Stability - vertical projection of muscular forces directing COM motion

1. Anticipatory postural adjustments

   • what we do before performing a task

   • most emphasized first

2. Ongoing postural adjustments

   • body segments implement in order to establish that stability in the performance of a task

3. Reactive postural adjustments

   • when external forces are applied

Postural Adjustments - Critical Biomechanical Components

Postural Sway

Small movement of the body mass about the BOS

• reduced strength

• peripheral sensation

• vision and reaction time

Causes of Postural Sway

• Arrow signifies anteroposterior movement

• Specific muscles work together to achieve a good postural control

• When pt. is taught to stand up for the first time, ensure that the muscles specified in the diagram

• If pt. learned to stand up s evaluating if the muscles are working, it can contribute to complications (e.g. back pain, hip pain)

• During posterior sway, abdominals should be working

Motor Mechanisms of Postural Control

• small amount of postural way

1. Body Alignment

   • can minimize the effect of gravitational forces which tend to pull us off center

2. Muscle Tone

   • Keeps the body from collapsing from the pull of gravity

Motor Control in Quiet Stance - Factors that contribute to stability

1. The intrinsic stiffness of the muscles themselves

2. The background muscle tone, which exists normally in all muscles because of neural contributions

3. Postural tone - the activation of antigravity muscles during quiet stance

Motor Control in Quiet Stance - Three main factors contribute to our background muscle tone during quiet stance

• postural control in response to sensory feedback

• Comes from visual, vestibular or somatosensory

  system

• Occurs with external perturbation

• Ex. when the support surface moves; during gait, unexpected disruptions to the gait cycle

Postural muscle synergies - Feedback control

• refers to postural responses that are made in anticipation of a voluntary movement that is potentially destabilizing

• Ex. prior to to a movement, when we lift a heavy object

Postural muscle synergies - Feedforward control

1. Ankle Strategy (25% of perturbation or push)

2. Hip Strategy (50% or more than the ankle strategy)

3. Stepping Strategy (If more than 50%, approximately 75% or more)

When a person is standing on a firm flat surface, there are 3 distinct step by step strategies that needs to be activated so that we can avoid falls:

Ankle Strategy

Most common response to minor anteroposterior translation of the supporting surface

• Anterior lower limb muscles to correct posterior destabilization; or

• Posterior limb muscles to correct anterior destabilization

Ankle Strategy - Muscles are activated in a distal → proximal sequence, either:

FORWARD SWAY	BACKWARD SWAY
Gastrocnemius hamstrings Paraspinal Muscles In standing, when you move your body forward, you will immediately do ankle PF.	Anterior Tibialis Quadriceps Abdominals When you move your body backward, you will immediately do ankle DF

Ankle Strategy - Forward sway vs Backward Sway

FORWARD SWAY	BACKWARD SWAY
Abdominals Quadriceps	paraspinal hamstrings

Hip Strategy - Forward sway vs Backward Sway

• A.k.a Stepping response

• Rapid steps, hops or stumbles that are made to form a new base of support for the body’s COM when ankle and hip strategies

• When ankle, hip are insufficient to recover balance, a STEP or HOP is used to bring the support back to alignment

• To avoid fall because of too much force

Stepping Strategy

Adaptive Learning

Modifications made by your sensory and motor systems in response to changing tasks and environmental demands

at the hip and trunk

• side by side weight shifting

Mediolateral stability occurs primarily at the _______

Flexors and Abductors

Mediolateral stability - NWB / Unloaded Limb

Extensors and adductors

Mediolateral stability - dWB / loaded Limb

Hips > Ankle stepping

when a person is standing on a narrowed surface, the ____ are performing much actively compared to the _______ strategy

Ankle → Hip → Stepping

Order of strategies on leveled surface

Hip → Ankle → Stepping

Order of Strategies on unleveled / narrow surface:

Perturbing Balance

Are mechanisms that the body implements to maintain stability when it is thrown off center by:

• an external force to the body

• via support surface environment

• internal forces during self-initiated movement

• Balance cannot be trained in isolation from the actions which must be relearned (Carr & Shepherd)

• Sensory and motor processes involved in the control of balance are task-specific

• Perform task using movements of the body mass (Carr & Shepherd)

• Individuals who cannot assume the upright position need to be assisted and may initially need to proactive reaching with some external concentration to control some components of segmental alignment

Training Guidelines

Normal

• Able to maintain steady balance without

  handhold support (static)

• Accepts maximal challenge and can shift weight easily within full range in all directions (dynamic)

Grade 4 Balance

Good

• Able to maintain balance without handhold support, limited postural sway (static)

• Accepts moderate challenge; able to maintain balance while picking object off floor (dynamic)

Grade 3 Balance

Fair

• Able to maintain balance with handhold support; may require occasional minimal assistance (static)

• Accepts minimal challenge; able to maintain balance while turning head/trunk (dynamic)

Grade 2 Balance

Poor

• Requires handhold support and moderate to maximal assistance to maintain position (static)

• Unable to accept challenge or move without loss of balance (dynamic)

Grade 1 Balance

Unable to maintain balance

Grade 0 Balance

• changing the shape of the base of support

• requiring increased flexion and extension of the legs

• Increasing object’s distance from the body

• Increasing and varying the object’s weight

• Increasing object’s size

• Changing the location of the object

• Increasing the speed demands

• Requiring a quick response (timed activities)

• Requiring that movement occurs in directions that are difficult for the individual

techniques in progressing training

• Adjustments we make to preserve balance are flexible and varied ○ Customized to the patient

  • Postural adjustments typically begin in muscles closest to the base of support

• Balance is constrained by the body’s dynamics, the physical environment and prior experience

• Balance emerges from a complex interaction between sensory and musculoskeletal systems

POINTS TO PONDER when implementing Interventions for balance

• Initial alignment

• Presence of feet support

• distance of reach

Factors influencing sitting balance

• Feet and knees close together

• Weight evenly distributed

• Shoulders over hips

• Head balanced on level shoulders

Factors influencing sitting balance - Initial Alignment

• Promote proper alignment of posture

• Active correction of alignment with verbal or visual cues

• Promote symmetrical weight distribution

Specific Strategies - Postural re-education

• Breathing exercises

• Self-initiated head and trunk rotation

• Looking up at the ceiling and down at the floor

Specific Strategies - head and trunk movements

• Reaching to touch a object

  • Done in various directions

  • May palace very weak affected arm initially on table

  • Ipsilateral then contralateral reach

• Reaching to pick up objects from the floor

• Forward and sideways

  • One hand to two hands

• Progression:

  • Increasing object’s distance from body

  • Increasing the object’s size and weight

  • Changing the location of the object

  • Increasing speed demands

  • Requiring a quick response

  • Requiring that movement occurs in directions that are difficult for the individual

Specific Strategies - reaching actions

• form of progression

• increasing distance to be reached

• varying speed

• reducing support

• increasing object weight and size involved both upper limbs

• Adding an external timing constraint such as catching or bouncing

Sitting Balance - Maximizing Skill

• Initial alignment

• Muscle tone - postural tone

• Forthcoming movement - anticipatory

• Speed and amplitude of movement

Factors Influencing Standing Balance

• Mastoid process

• Point in front of the shoulder

• Through or slightly behind the hop

• In front of the knee

• In front of the ankle

Factors Influencing Standing Balance - Initial balance

• weakness

• sensory impairments

• adaptive behaviors

Impairments underlying poor balance

• Contributes to decrease in force generation, force initiation, timing and sequences

• Difficulty in sustaining the force of movement for the patient will be able to generate force but would not be fast enough

• Abnormal motor control

Impairments underlying poor balance - weakness

• Widening the BOS

• Using the hands for support

• Shifting on to the less affected side

• Stiffening the body

• Avoiding the threat to balance

• Disuse of paretic side

• Improper posture

Impairments underlying poor balance - Adaptive behaviors

• COG over the BOS in a given activity within or beyond the LOS

• Develop necessary and quick response and strategies to known and unknown external perturbations

• Prevent or reduce impairments in systems that are important to balance (e.g. adaptive shortening of LE soft tissues)

• Increase LE muscle strength and coordination to support body mass

• Refrain functional tasks with varying postural control demands

General goals of rehabilitation

• Prevent adaptive shortening of the lower extremity soft tissues

• Increases lower extremity muscle strength and coordination to support body mass

Goals of rehabilitation - Impairment Level

• Control of COG over BOS in a given activity within or beyond the LOS

• Retrain sensory strategies

• Develop necessary responses to external perturbations

Goals of rehabilitation - Strategy Level

• We train tasks and activities in which the patient is exposed more frequently

• Control in specific ways and environments

Goals of rehabilitation - Function Level