Balance and PostureAndrew L. McDonough

What is Balance?Technically defined as the ability to maintain the center-of-gravity (COG) of an object within its base-of-support (BOS)

What is Posture?The stereotypical alignment of body/limb segmentsTypesStanding (static)Walking - running (dynamic)SittingLyingLifting

Relationship - Balance & PosturePostural alignment (and the changes/adjustments made due to perturbations) is the way balance is maintainedMaintaining the COG within the BOSIf this relationship isnt maintained then a system will be unbalanced

Base of SupportxH-HTM-L TM-Rx - Vertical projection of COGWalkingxStaticDynamic

Transition - Static to Dynamic BOSHeel-to-heel distance will decreaseFeet come together toward midlineToe-to-midline distance will decreaseReflects toe-inOverall effect - BOS narrows

The Effect of a Narrowed BOSChances of COG falling within BOS decreaseSubject becomes less (un-) balancedCOG moves forward of BOS - precursor event to walkingFoot will be advanced to extend the dynamic BOS

Center-of-GravityThe point about which the mass is evenly distributedThe balance pointIf an object is symmetrically loaded the COG will be at the geometric center

Center of Gravity of Human Limbs and SegmentsLimbs/segments are usually asymmetrically loadedCOG tends to be off-centerCloser to the heavier endSourcesDempster (1955)Braune and Fischer (1889)Winter (1990s)

DempsterSubjects were 150 lbs. males (astronauts - NASA)COG located at a point as a percentage of total limb lengthKneeAnkle43.3% 56.7%Total limb length

Location of COGEntire bodySuprapedal massSuprafemoral massHATHeadS1 - S2ASISUmbilicusXiphoid processOcciput

Example: Change in the Location of the COG of Body - Right Unilateral AK AmputeeCOG will shift upward and to the left

Question: How will this change affect the patients perception of balance?

Answer: Profoundly!

General RuleAs COG shifts upward the object/subject becomes more top-heavyIncreases the tendency to be over-thrownMoment armMoment arm

Role of Anti-gravity Postural MusclesGenerate torque across joints to: Resist the tendency to be over-thrownKeep limbs, joints, body segments in proper relationship to one another so that the COG falls within the BOS

Some Examples - QuestionsWhat happens to the COG & BOS in:Someone walking along a sidewalks and encounters a patch of iceThe toddler just beginning to walkThe surfer coming down off of a waveThe tight-rope walker who loses her balance

A Systems Model of Balance11Courtesy of Sandra Rader, PT, Clinical Specialist

Stability & BalanceResult of interaction of many variables (see model)Limits of Stability - distance in any direction a subject can lean away from mid-line without altering the BOSDeterminants:Firmness of BOSStrength and speed of muscular responsesRange: 80 anteriorly; 40 posteriorly

Limits of Stability

Model ComponentsMusculoskeletal SystemROM of jointsStrength/powerSensationPainReflexive inhibitionAbnormal muscle toneHypertonia (spasticity)Hypotonia

Model ComponentsGoal/Task OrientationWhat is the nature of the activity or task?What are the goals or objectives?

Model ComponentsCentral SetPast experience may have created motor programsCNS may select a motor program to fine-tune a motor experience

Model ComponentsEnvironmental OrganizationNature of contact surfaceTextureMoving or stationary?Nature of the surroundsRegulatory features of the environment (Gentile)

Model ComponentsMotor CoordinationMovement strategiesBased on repertoire of existing motor programs Feedback & feedforward controlAdjustment/tuning of strategies

Strategies to Maintain/Restore BalanceAnkleHipSteppingSuspensory

Strategies are automatic and occur 85 to 90 msec after the perception of instability is realized

Ankle StrategyUsed when perturbation is SlowLow amplitudeContact surface firm, wide and longer than footMuscles recruited distal-to-proximalHead movements in-phase with hips

Ankle Strategy

Hip StrategyUsed when perturbation is fast or large amplitudeSurface is unstable or shorter than feetMuscles recruited proximal-to-distalHead movement out-of-phase with hips

Hip Strategy

Stepping StrategyUsed to prevent a fallUsed when perturbations are fast or large amplitude -or- when other strategies failBOS moves to catch up with BOS

Suspensory StrategyForward bend of trunk with hip/knee flexion - may progress to a squatting positionCOG lowered

Model ComponentsSensory OrganizationBalance/postural control via three systems:SomatosensoryVisualVestibular

Somatosensory SystemDominant sensory systemProvides fast inputReports informationSelf-to-(supporting) surfaceRelation of one limb/segment to anotherComponentsMuscle spindleMuscle lengthRate of changeGTOs (NTOs)Monitor tensionJoint receptorsMechanoreceptorsCutaneous receptors

Visual SystemReports informationSelf-to-(supporting) surfaceHead positionKeep visual gaze parallel with horizonSubject to distortionComponentsEye and visual tractsThalamic nucleiVisual cortexProjections to parietal and temporal lobes

Vestibular SystemNot under conscious controlAssesses movements of head and body relative to gravity and the horizon (with visual system)Resolves inter-sensory system conflictsGaze stablizationComponentsCerebellumProjections to:Brain stemEar

Sensory-Motor IntegrationSomatosensoryVestibularVisualEye Movements

Postural Movements10 Processor20 ProcessorCerebellumMotoneuronsSensory InputProcessingMotor Response

What is Posture?The stereotypical alignment of body/limb segmentsTypesStanding (static)Walking - running (dynamic)SittingLyingLifting

PosturePosition or attitude of the bodyPostural sets are a means of maintaining balance as weve defined itStanding (static)Walking - running (dynamic)SittingLyingLifting

What Does Posture Do for Us?Allows body to maintain upright alignmentPermits efficient movement patternsAllows joints to be loaded symmetricallyDecreases or distributes loads onLigaments and other CTMuscleCartilage and boneGood posture usually results in the least amount of energy expended

Erect Standing Posture & the Gravity Line (Sagittal Analysis)Gravity line falls:Forward of ankleThrough or forward of the kneeThrough of behind the hip (common hip axis)Behind or through thoracic spineThrough acromiumThrough or forward of atlanto-occipital jt.

Erect Standing Posture & the Gravity Line (Frontal Analysis)Gravity line falls:Symmetrically between two feetThrough the umbilicusThrough the xiphoid processThrough the chin & noseBetween the eyes

The Gravity Line and Anti-gravity Muscles (Sagittal Plane)Gravity line falls:Forward of ankleThrough or forward of the kneeThrough of behind the hip (common hip axis)Behind or through thoracic spineThrough acromiumThrough or forward of atlanto-occipitalAnti-gravity muscle:Gastroc-soleusQuadriceps

Hip extensors

Paraspinals

Neck extensors

Relaxed vs. Military Standing PostureThe Military Posture requires ~30% more energy expenditure compared with a more relaxed upright standing posture

Sitting PostureDisc patients often cannot sitIncreased intra-disc pressure compared with standingOften loss of lordotic curve - may reverse leading to asymmetrical disc loading

Sitting Posture - ElementsBack against chairLumbar supportSeat heightDont allow feet to dangle or knees too highSeat lengthToo long forces loss of lordosisFeet flat with hips & knees at ~900Forearms supported

Lying (Sleeping) PostureElementsFirm mattress for supportNot too many pillows - Maybe noneLying flat on back may decrease lordosisHook-lying may preserve lordosisSide-lying may be more comfortable

Lifting Posture - PTs vs. PatientsControl COG (PTs & patients) vs. BOSDont over-extend while reaching for patientLoad LEs symmetrically - NO rotation!Maintain correct spinal curvature - especially lumbar spineSpine should NOT be straight - maintain lordosisThink about a power lifterLeverage vs. brute force

Remember...Get Help!

Remember...Get Help!Most SuperPTs have LBP & disc disease!