Biomechanics Poture Analysis

8/11/2019 Biomechanics Poture Analysis

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PostureMahmooda Naqvi

Sr. Lecturer

BPT,PPDPT


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Posture

Posture is a position or attitude of

the body, the relative arrangement of

body parts for a specific activity

It is alignment of the body partswhether upright, sitting, orrecumbent.


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Posture

It is the attitude which is assumed

by body parts to maintain stability

and balancewithminimum effortand least strainduring supportive

and non supportive positions.


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Posture

Can be

DynamicStatic


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For any stationary posture to be

maintained, two rules of equilibrium

must be satisfied:

A vertical line,directly throughcentre of gravityof the body must

fall within thebodys base ofsupport.

The net torque (ormoment) abouteach articulationof the body must

be zero.


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Types of static postures


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Dynamic posture

Postures in which the body or its segments

are moving.

This posture is adopted while the

body is in action, or in the anticipatory

phasejust prior to an action occurring.Eg: walking, running,

jumping, throwing, and lifting.


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Raising arm and single stance


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CORRECT POSTURE

Is the position in which minimum

stressis applied to each joint. This

stress should remain minimalduring rest and while in activity.


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DEVELOPMENT OF GOOD POSTURE

A stable psychological

background

Good hygienic conditionsOpportunity for plenty of

natural free movement


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Is Correct Posture Applicable To Both Static Or

Dynamic Posture


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Applicable to bothstatic and dynamic postureslike standing, sitting, lying,

walking, lifting.


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Good posture in standing


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GOOD DYNAMIC POSTURE


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FAULTY POSTUREAny static position thatincreases the stressto the

joints may be called faulty

posture.

Impairments in the joints,

muscles, or connective tissue

(ligaments, capsule) may

lead to faulty posture.


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FAULTY POSTURE

Faulty postures may lead to impairments in the

joints, muscles and connective tissues as well assymptoms of discomfort and pain.

Manymusculoskeletal complaints

can be attributed to stresses that

occur from repetitive or sustained

activitieswhen in habitually

faulty postural alignment.


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IS RELAXING POTURE IS AGOOD POTURE


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POSTURAL MUSCLES

Postural muscles act predominantlytosustainposture in the gravity field.

These muscles contain mostly slow-

twitch muscle fibers and have agreater capacity for sustained work.


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POSTURAL MUSCLESShoulder girdle-Arm Trunk Pelvis- Thigh Lower leg- Foot

Pectoral Muscles

Levator Scapulae

Trapezius (upper)

Biceps Brachii

Scalenes

Subscapularis

Sternocleidomast

oidSuboccipitals

Masseter

Temporalis

Wrist & Finger

Flexors

Lumbar Erector

Spinae

Cervical Erector

SpinaeQuadratus

Lumborum

Hamstrings

Iliopsoas

Rectus Femoris

AdductorsPiriformis

Tensor Fasciae

Latae

Gastrocnemius

Soleus


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FACTORS AFFECTING

POSTUREFaulty posture may be caused

due to:a.Structural factors

b.Postural/Positional factors


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STRUCTURAL FACTORS

Structural deformities which are the

result of congenital anomalies,

developmental problems, trauma, ordisease, may cause alteration of

posture.

Eg: A significant difference in leg

length or an anomaly of spine.


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STRUCTURAL FACTORS

Structural deformities involve

mainly changes in bone Are not easily correctable without

surgery. Relieved of symptoms by proper

postural care instructions.


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POSTURAL (POSITIONAL)

FACTORSThe most common postural problemis poor postural habit. Whatever the

reason may be, the patient does notmaintain correct posture.

The majority of postural non

structural faults are relatively easy tocorrect after the problem has been

identified.


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POSTURAL (POSITIONAL) FACTORS

The treatment involves

strengthening weak muscles,

stretching tight structures, andteaching the patient to maintain a

correct upright posture instanding, sitting and other

activities of daily living.


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Postural factors

The functional incorrect posture

may be seen in the following:

Prolong standing or sitting and then begins to slouch.


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In children not wanting to appear taller thanones peers.Eg: Tight hamstrings in

adolescents due to early growth of bone and

slow growth of muscle.


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Muscle imbalance or muscle

contracture.

Eg: Tight iliopsoas increases

lumbar lordosis in the lumbar spine.


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Pain-The person suffering from

pain may adapt certain posture

so as to relieve pain.

Respiratory conditions

Eg: Emphysema


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Excess weight loss

Loss of proprioception

Muscle spasm

Eg: Cerebral palsy


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Postural Sway In standing position,

there is a continuousmovement due to

alternating action of

antagonistic muscle

groups working toresist gravitationalstresses.

This work keeps thetotal centre of gravityof the body within the

bodys base of

support.


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Postural Sway

The abovecontinuousmovement results

in a slight anteriorposterior swayingof the body of body

Approx 4cmexcursion calledthe postural sway

or sway envelop.

P l S


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Postural Sway

The extent of the swayenvelop for a normalindividual standing with 4inches feet apart can be

as large as

12in the sagittalplane

16

o

in the frontalplane


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Vision is the mostimportant factor inreducing postural sway.

Fixating the vision on agiven point lessensexcursion.

Postural sway variesacross the lifespan, beinggreatest in the young andelderly.


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Postural control

Postural control which can either bestatic or dynamic, refers to the persons

ability to maintain stability of the bodyand body segments in response toforces that threaten to disturbthe

bodys equilibrium.Brought about by the activity of the

Central Nervous System.


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Maintenance and control of posturedepends on the integrity of the CNS, visualsystem, vestibular and musculoskeletalsystem.

Postural control also depends oninformation received from receptorslocated in and around thejoints(in joint

capsules, tendons, and ligaments), as wellas the soles of the feet, muscles,eyes, skinand ears.


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PerturbationsPerturbation is any sudden change inconditions that displacesthe body postureaway from equilibrium. They can be:

Sensory:

Caused by altering visual,

sensory input.

Eg: Such as covering a

persons eye unexpectedly.


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Mechanical: Caused by movements of eitherbody segment orentire body.

Mechanical perturbations are displacements that

involve direct change in the relationship of thebodys CoM to the BoS.

Pushing someone


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Breathing can displace CoM.

Perturbation in standing that result

from respiratory movements ofthe ribcage are counterbalanced

by movements of the trunk andlower limb.


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Response

The Central Nervous System interprets andorganizes inputs from the various structures andsystems and selects responses on the basis ofpast experience and the goal of the response.

Reactive (compensatory) response: Occurs asreactions to external forces that displace thebodys COM.

Proactive (anticipatory) response: Occurs in theanticipation of internally generated destabilizingforce such as raising arms to catch a ball orbending forward to tie shoes.


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CENTRE OF MASS

It is the point on an object at whichthe relative position of the distributed

mass sums to zero

The point about which objects rotate.


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Cont

Although a human body has complicated features, thelocation of the center of mass (COM) could be a goodindicator of the body proportions.

The center of mass of the human body depends on thegender and the position of the limbs.


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Cont

In a standing posture, it is typically about 10

cm lower than the navel, near the top of thehip bones.

Motion of the whole bodys center of


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ymass when stepping over

obstacles of different heights Tripping over obstacles and imbalance during gait were reported as two of

the most common causes of falls in the elderly. Imbalance of the wholebody during obstacle crossing may cause inappropriate movement of thelower extremities and result in foot-obstacle contact. Thus, this study wasperformed to investigate the effect of obstacle height on the motion of thewhole bodys center of mass (COM) and its interaction with the center ofpressure (COP) of the stance foot while negotiating obstacles. Six healthyyoung adults were instructed to perform unobstructed level walking and tostep over obstacles of heights corresponding to 2.5, 5, 10, and 15% of thesubjects height, all at a comfortable self-selected speed while walkingbarefoot. A 13-link biomechanical model of the human body was used tocompute the kinematics of the whole bodys COM. Stepping over the higherobstacles resulted in significantly greater ranges of motion of the COM inthe anterior-posterior and vertical directions, a greater velocity of the COMin the vertical direction, and a greater anterior-posterior distance betweenthe COM and COP. Incontrast, the motion of the COM in the medial-lateraldirection was less likely to be affected when negotiating obstacles ofdifferent height(Li-Shan Chou a,1, Kenton R. Kaufman a,*, Robert H. Breyb, Louis F. Draganich)

t d f t l t l i Idi thi


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study of postural control in Idiopathic

Scoliosis patients: a comparison of two

techniques The objective of the present study is to quantify the position of the Centre of Mass (COM)

during quiet standing using a force plate and compare this technique to the quantification ofthe COM with an anthropometric model. The postural control of 18 healthy adolescents and22 IS patients was evaluated using an Optotrak 3D kinematic system, and two AMTI forceplates during quiet standing. The position of anatomical landmarks tracked by the Optotrak

system served to estimate the position of the COM of both groups using an anthropometricmodel (COManth). The force plate served to estimate the position of the COM throughdouble integration of the horizontal ground reaction forces (COMgl). The mean position androot mean square (RMS) amplitude of COMgl, in reference to the base of support (BOS) andthe first sacral prominence (S1) were quantified in the AnteriorPosterior (A/P) and MedialLateral (M/L) directions. There was a significant difference between the control subjects andIS patients for the displacement of the COMgl in reference to the BOS in both the A/P andM/L directions. There was no difference between groups for the mean position of the COMgl,however, 63% of the IS and 43% of the controls had a lateral position of the COMgl inreference to S1 of greater than 5 mm. There was a significant difference between groups inthe A/P and M/L directions for the amplitude of error between the COMgl and COManthtechnique


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Muscle synergies/strategies

Horak and associates described synergiesas centrally organized patterns of muscleactivity that occur in response toperturbations of standing postures. The

three types of muscle synergies include:

1.Fixed-support synergies2.Change-in-support synergies3.Head-stabilizing synergies ----

Proactive

Reactive


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Strategies are automatic and occur 85

to 90 msec after the perception of

instability is realized


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1. Fixed-support synergies

Stability is regained throughmovements of body parts, but feetremains fixed on the BOS.


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Ankle-strategy:

Involves shifting of the CoM forward

and back by rotating the body as a

relatively fixed pendulum about the

ankle joints.

Most commonly used strategy when

disturbances are small, well within theBOS or LOG.


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ANKLE STRATEGY

Used when perturbation is

Slow

Low amplitude

Contact surface firm, wide and longer than foot

Muscles recruited distal-to-proximal

Head movements in-phase with hips


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Hip-strategy

Involves shifts in the COM byflexing or extending the hips.

The hip strategy is recruitedwith larger and faster

disturbances of the CoM.


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HIP STRATEGY

Used when perturbation is fast or large amplitude

Surface is unstable or shorter than feet

Muscles recruited proximal-to-distal

Head movement out-of-phase with hips


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Perturbation of erect stance equilibrium causedby backward horizontal platform movement.A. Posterior movement of the platform causes

anterior movement of the body and, as aconsequence, displacement of the bodysCoM anterior to the base of support.

B. B. Use of the ankle strategy (activation ofthe extensors at the ankle, hip, back, andpossibly neck) is necessary to bring thebodys CoM over the base of support andreestablish stability.

Perturbation of erect stance equilibriumcaused by forward horizontal platform movement.A. Anterior (forward) movement of the platform

causes posterior (backward) movement of thebody and, as a consequence, displacement ofthe bodys CoM posterior to the base of support.

B. B. Use of the ankle strategy (activation of theflexors at the ankle, hip, trunk, and possiblyneck) is necessary to bring the bodys CoM backover the base of support and reestablishstability.


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2. Change-in-support strategies

Are defined as movements of the

lower or upper limbs to make a new

contact with the support surface.

Include stepping and grasping in

response to shifts either in the BOS orthe entire body


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The stepping strategies are

recruited in response to fast,larger perturbations.


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3. Head-stabilizing strategy

Occurs in an anticipation of the internally generatedforces caused by changes in position from sitting tostanding.

Are used to maintain the head during dynamic tasks suchas walking.

a. Head stabilization in space (HSS):. These anticipatoryadjustments of head position are independent of trunk

movement.

b. Head stabilization on trunk (HST): Is one in which the head andtrunk moves as a single unit.


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Kinetics and kinematics of posture

There are both internal and external forces acting upon the body.

Different structures of the body serve to provide active internal forces in order tocounteract the external forces that affect the equilibrium and stability of thebody.

Some of the external forces acting upon the body which are of biomechanicalimportance include inertia, gravity, and ground reaction forces (GRFs).

The internal forces are produced by muscle activity and passive tension in

ligaments, tendons, joint capsules and other soft tissue structures. The sum of all of the external forces and internal forces and torques acting on the

body and its segments must be equal to zero for the body to be in equilibrium.


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Inertial and gravitational forces

In the erect standing posture, little or no acceleration of the

body occurs.

Gravity places stress on the structures responsible for

maintaining the body upright therefore affecting stability and

efficient movement.

For a weight bearing joint to be stable or in equilibrium, theLoG must fall exactly through the axis of rotation, or there

must be force to counteract the moment caused by gravity.


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Ground reaction forces

when the body contacts a ground ,the ground pushes back on to thebody. This force is known as Ground Reaction Force (GRF).

The vector representing GRF is known as the Ground Reaction ForceVector (GRFV).

The GRF is a composite (or resultant) force that represents themagnitude and direction of loading applied to one or both feet.

It has three components:

A verticalcomponent force (along the y-axis). Twoforce components directed horizontally: Medial lateral direction (along x-

axis) and Anterior Posterior direction(along z-axis)

The point of application of GRFV is at bodys Centre of pressure (COP)


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Coincident action lines

In an ideal erect position, body segments are aligned in such a

way so as to minimize the torques and stresses on the bodytherefore reducing the energy expenditure.

The coincident action lines formed by GRFV & LoG are used to

study effects of these forces on the body segments.

The location of LoG & CoP shifts continually because ofpostural sway. This results in continuous changing moments

created around the joints.


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External and internal moments

External gravitational moments are created when the LoG passesat a distance from the joint axis. This moment causes rotation ofthe superimposed body segments around that joint axis.

This rotation has to be opposed by a counterbalancing internalmoment provided by muscle contraction.

If LoG is located anterior to a particular joint axis, the gravitationalmoments cause anterior motion of the proximal segment of the

body supported by that joint (Flexion moments). If LoG is posterior to the joint axis, the moment will cause a

posterior motion of the proximal segment (Extension moment).


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Refrences

Joint structure and function by Cynthia C. Norkin (5th

edition)

Therapeutic exercises by Kisner and Colby (5thedition)

Orthopedic assessment by Magee

BrunnstromsClinical Kinesiology (5thand 6thedition)

Physical rehabilitation by Susan O sullivan


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Thank you

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Biomechanics Poture Analysis