postural biomechanics

1. POSTURE
T. YASWANTHI
(MPT)

2. DEFINITION
 Posture can be defined as the
relative arrangement of
different parts of the body with
line of gravity.
 Each structure contributes to
equilibrium and stability of body
in optimal standing position.

4. TYPES OF POSTURE
 Humans have the ability to arrange and
rearrange body segments to form a large variety
of postures. ( Erect bipedal stance )
STATIC POSTURE :
 The body and its segments are aligned and
maintained in certain positions.
 Examples : standing, sitting, lying, and kneeling.
DYNAMIC POSTURE :
 postures in which the body or its segments are
moving
 Examples : walking, running, jumping, throwing,
and lifting.

5. POSTURAL CONTROL
 It is the persons ability to maintain-stability of
body and body segments in response to forces that
disturb the body’s structural equilibrium
 Postural control depends on integrity of CNS,
visual, vestibular, and musculoskeletal system.
 It also depends on information from receptors
located in and around joints and from sole of foot.
 Reactive responses –reactions to external that
displaces body COM
 Proactive response—internally generated
destabilizing forces
 Example :rising arms to catch a ball

6. MAJOR GOAL AND BASIC ELEMENTS OF
CONTROL
 Major goals :
 Control body’s orientation in space
 Maintain body’s COG and BOS
 Stabilize the head vertically –eye gaze is
appropriately oriented
 Elements of control :
 CNS is able to detect instability and respond to
the input with appropriate output to maintain
equilibrium of body.
 Musculoskeletal system have ROM for
responding to specific tasks
 Muscles able to respond with appropriate
speed and forces.

7.  ABSENT OR ALTERED INPUTS :
o When inputs are altered , control
system respond to incomplete data and
posture may be altered .
Example : foot “FALLEN ASLEEP”.
 ALTERED OUT PUTS :
o Inability of muscles to respond to appropriately
to signals from CNS.
o Example : sedentary elderly persons .

8. MUSCLE SYNERGIES
 “PERTURBATION” is any sudden change in
conditions that displaces the body posture
away from equilibrium .
perturbation
SENSORY MECHANICAL
(Altering of visual (displacements-movements
input) of body segment or entire
body [COM to BOS ])
 Postural response to perturbations caused by
either platform or by pushes or pulls are called
REACTIVE or COMPENSATORY response.

9. SYNERGIES
 Fixed support synergies
 Change in support synergies
 Head supporting strategies
The postural responses are called SYNERGIES
or STRATEGIES

10. FIXED SUPPORT SYNERGIES:
 Pattern of muscle activity in which the BOS
remains fixed during the perturbation and
recovery of equilibrium.
 Stability is regained through movements of
parts of the body but ,the feet remains fixed
on BOS.
 EXAMPLES: Ankle synergy ,Hip synergy
ANKLE SYNERGY:
 It consists of discrete bursts of muscle activity
on either the anterior or posterior aspects of
the body that occur in response to forward and
backward movements of the supporting
platform .
 Muscle activity from distal to proximal pattern.

11. ANKLE SYNERGY
 Anterior (forward)
movement of platform
 Posterior (backward)
movement of body---
displacement of body’s
LOG posterior to BOS.
 Activation of dorsiflexors,
hip flexors, abdominal
muscles, neck flexors
 LOG back over BOS
STABILITY

12. ANTERIOR PERTURBATION
 Posterior movement of
platform
 Anterior movement of
body----displacement
of body’s LOG anterior
over BOS
 Activation of plantar
flexors ,hip extensors
, back and neck
extensors
 LOG back over BOS --
---STABILITY

13. HIP SYNERGY
 It consists discrete bursts of muscle activity
in a proximal-to-distal pattern of activation.
 Fixed-support hip synergy may be used
primarily in situations in which change-in-
support strategies (stepping or grasping
synergies) are not possible

14. CHANGE-IN-SUPPORT SYNERGIES
 Strategies include stepping
(forward, backward, or
sidewise) and grasping (using
one’s hands to grab a bar or
other fixed support) in response
to movements of the platform.
 Maintains stability in instance
of large perturbations.
Tether-release system.
Backward movement of platform,
person uses steeping strategy to
keep from falling forward .it brings
body’s COM over a new BOS.

15. HEAD STABILIZING STRATEGIES
 Proactive strategy occur in anticipation of
initiation of internally generated forces caused by
change in position from sitting to standing.
 Used in dynamic equilibrium situation.
Example : maintain head during walking.
 Vertical stability of head is maintained by two
types of strategies
 HEAD STABILIZATION IN SPACE (HSS):
Modification of head position in anticipation of
displacements of body COG.
 HEAD STABILIZATION ON TRUNK (HST):
Head and trunk move as a single unit.

16. KINETICS AND KINEMATICS OF POSTURE
 In response to perturbations, active internal
forces employed to counteract the external forces
that affect the equilibrium and stability of the
body in the erect standing posture.
 External forces : Inertia, Gravity and ground
reaction forces (GRF’S)
 Internal forces : Muscle activity, passive tension
in ligaments, tendons, joint capsules and other
soft tissue structures .
 INERTIA: In erect standing posture body undergoes
a constant swaying motion called postural sway
or way envelop (4inches b/w feet—12 in sagittal
plane ,16 in frontal plane)
 GRAVITY: Forces acts downward from body’s COG
(LOG falls within BOS)

17. GROUND REACTION FORCES :
 When ever body contacts the ground , the ground
pushes back on body (GRF )
 Vector representing it is called GRFV.
 GRF have 3 component forces
1 vertical component force
2 horizontal component forces
- Medial and lateral direction
- Anterior and posterior direction
 GRFV is equal in magnitude but opposite in direction
to GF in erect standing posture
 The point of application of GRFV is at body’s centre of
pressure (COP)
 COP is located in foot in unilateral stance and b/w feet
in bilateral stance.

18. COINCIDENT ACTION LINES :
 GRFV and LOG have coincident action lines
in static erect posture.
 It help to analysis of effect of these forces
on body segments.
External and Internal movements:
 LOG passes at a distance from axis, an
external gravitational moment is created
and it causes rotation of superimposed
body segments around that joint axis
unless it opposed by counterbalancing
internal moment (muscle contraction).

19. OPTIMAL POSTURE
 An ideal posture is one in which the body segments are
aligned vertically and LOG passes through all the joint
axes
 Normal body structures makes it impossible to achieve,
but is possible to attain a posture, close to ideal one
 In normal standing posture ,the LOG falls close to, but
not through most jt. axes -Compressive forces are
distributed over the weight bearing surfaces of joints; no
excessive tension exerted on ligamentous or required
muscles
Analysis of Posture from side view:
Analysis of posture involves identification of the location of
body segments relative to the LOG
 Body segments-either side of LOG- symmetrical
 A plumb line is used to represent the LOG
 Postural analysis may be performed using; Radiography,
photography, EMG, electro goniometry, force plates, 3-
dimensional computer analysis

20. ALIGNMENT AND ANALYSIS:
LATERAL VIEW
ANKLE:
 LOG passes slightly anterior to lateral malleolus

21. ANALYSIS OF KNEE IN SIDE VIEW
KNEE :
 LOG passes anterior to midline of knee and posterior to patella.

22. HIP AND PELVIS ANALYSIS IN SIDE VIEW
 LOG passes slightly posterior to axis of hip joint, through
greater trochanter leads to posterior pelvic tilt on femoral
head.

23. SWAYBACK POSTURE
 LOG falls farther behind the
hip joint axis than optimal
posture

24. Analysis of lumbosacral and sacroiliac joint

25. ANALYSIS OF
VERTEBRAL COLUMN
 Optimal position of plum line
through midline of trunk.
 At cervical- LOG posterior,
extension
 At thoracic- LOG anterior,
flexion
 At lumbar- LOG posterior,
extension

26. ANALYSIS OF HEAD

27. Deviations from optimal alignment
view from side
 Foot and Toes:- Claw toes
Hammer toes
 Knee:- Flexed Knee Posture -Genu Recurvatum
 Pelvis:-Excessive Anterior Pelvic Tilt
Excessive posterior pelvic tilt
 Vertebral column:- Lordosis
Kyphosis
 Head:- Forward Head Posture

28. CLAW TOES :
 Hyperextension of MTP joint, flexion of PIP and DIP joints.
 Callus (thickening of epidermis )Formation on dorsal aspect of
flexed phalanges. Affects all toes (2nd through 5th)
Hammer Toe :
 Deformity-hyperextension of MTP and DIP joints - flexion of PIP
joint.
 Callus on superior surface of PIP joints

29. FLEXED KNEE POSTURE
 This stance is maintained by
increased activity by
quadriceps, gastrocnemius,
soleus, and hip extensors

30. GENU RECURVATUM
 The hyper extended knee
posture, LOG locates anteriorly,
puts the posterior joint capsule
under tension stress and
lengthening of posterior capsule,
cruciate ligament.
 Anterior compression leads to
degenerative changes of
cartilaginous joint surface.

31. PELVIS
 Excessive Anterior Pelvic
Tilt
 Excessive Posterior
Pelvic Tilt
 Straightening of lumbar
spine and loss of
flexibility and also loss
its ability to withstand
high load.

32. VERTEBRAL COLUMN
 Kyphosis: It refers to an abnormal
increase in the normal posterior
convexity of the thoracic vertebral
column.
Two types :
 Gibbus Hump Back is a deformity that
may occur as result of TB. It forms a
sharp posterior angulation in the upper
thoracic region of vertebral column
 Dowager’s Hump is found in post-
menopausal women with osteoporosis.
Anterior aspect of bodies of series of
vertebra collapse due to osteoporotic
weakening and therefore, increase in
posterior convexity of thoracic area
 Lordosis: It refers to an abnormal
increase in the normal anterior
convexities of either the cervical or
lumbar regions of the vertebral column

33. HEAD
Forward head posture :
 Anterior location LOG ,increases flexion
movement this leads to increase constant
isometric muscle tension to support forward
head posture
 Compression of posterior zygapophyseal joints
and posterior intervertebral disc and
narrowing of intervertebral foramen in
lordotic areas of cervical region.

34. ANTERIOR AND POSTERIOR VIEW OF
LOG

35. OPTIMAL ALIGNMENT AND ANALYSIS
IN ANTERIOR AND POSTERIOR VIEW

38. PES PLANUS (FLAT FOOT )
 Reduced or absent MEDIAL LONGITUDINAL ARCH,
which may be either rigid or flexible
 Talar head-displaced-anterior, medial, inferior
and causes depression of navicular bone and
plantar calcaneonavicular (spring) ligament, and
lengthening of tibialis posterior muscle
 Navicular lies below the Feiss line and may even
rest on the floor in severe conditions

39. RIGID FLAT FOOT
 It is a structural deformity where the medial
longitudinal arch of foot is absent in NWB,WB
and toe standing
 The arch is reduced during normal weight
bearing, but reappears during toe standing and
non weight bearing
FLEXIBLE FLAT FOOT

40. PES CAVUS
 The medial longitudinal arch of foot may be
unusually high
 A high arch is called pes cavus
 It is a more stable position of foot than pes
planus
 Weight borne on lateral borders of foot
 Lateral ligament and peroneus longus
muscle stretched

41. KNEES
GENU VALGUM (Knock knees)
 Mechanical axes of lower extremities are
displaced laterally and patella may be
displaced laterally
 If genu valgum exceeds 30° (50 to 70 ) persists
beyond 8yrs of age – structural changes occur
 Medial knee joint structures – abnormal
tensile or distraction stress
 Lateral knee joint Structures – abnormal
compressive stress

42. GENU VARUM (Bow legs )
 Knees are widely separated when the feet
are together and malleoli touches.
 Cortical thickening on medial concavity –
on femur and tibia due to increased
compressive force
 Patella may be displaced medially
 Causes—vit D deficiency, renal rickets ,
osteochondritis.

43. VERTEBRAL COLUMN

44. Idiopathic scoliosis are categorized by age
infantile (0 to 3yrs ),
juvenile (4 to 10yrs),
adolescent (older than 10yrs)

46. ANALYSIS OF SITTING
POSTURES
 Sitting postures are more complex than
standing postures.
 The same gravitational moments as in
standing posture must be considered,
 The contact forces that are created when
various portions of the body interface with
various parts of chairs, such as head, back,
and foot rests, and seats.

47. TYPES OF SITTING POSTURES
 Active erect sitting posture
 Relaxed erect sitting posture
 Slumped posture
 Slouched posture

48. MUSCLE ACTIVITY IN SITTING
POSTURES
 Static erect posture: LOG close to joint axis in head
and spine
 Slumped posture : LOG passes anterior to joint axis
 Slouched posture : LOG passes posterior to joint axis
 Flexion relaxation phenomenon helps to less muscle
activity in slouched posture than active erect sitting.
 Muscles activity help in sitting posture-superficial
lumbar multifidus, thoracic erector spinae, internal
oblique abdominal muscles

49. Intervertebral disc pressure and
compressive loads on spine
 IVD pressure is measured by creep phenomenon
 Compressive force by calculating muscle activity
with electromyography
 Flexed sitting posture is more harmful than
extend sitting posture
 Because in kyphosis sitting increased
intervertebral disc shear force
 Posterior annulus tensile force and anterior
anulus load, hydrostatic force in nucleus and
load on posterior ligaments

50. Seat interface pressures
 Contact forces between persons body and seat are called seat
interface pressure
 Measured by sensory-containing mats
 Force per unit are measured by pascals
 Individuals with physical disabilities (paraplegia), thin elderly
persons have higher pressure
 Wheel-chair users have high tension, compression, shear forces
in gluteus muscles
 Less muscle thickness under ischial tuberosity in elders
 These measurements help to prevent pressure sores
 To reduce seat interface pressure
 Change the posture of body-forward and lateral trunk flexion
 Alteration in angulation of chairs back rest
 Using cushions (synthetic material, water, air, gel)reduces stress
 Cushion thickness should be up to 8cm is useful

51. ANALYSIS OF LYING POSTURE
 Interdiscal pressures are less in lying posture
than in standing and sitting postures.
 Interdiscal pressures in supine lying (0.10 mpA)
were less than in either lying prone (0.11 mpA)
or lying on the side (0.12 mpA).
 Some pressure-reducing mattress surfaces
include foam, air, gas, water and gel.
 Other pressure-relieving surfaces include
movable surfaces, usually powered by a motor
or pump, which can alternatively inflate and
deflate.

52. Factors affecting posture alignment