This document provides an overview of posture biomechanics, including: 1. Definitions of static and dynamic posture, and descriptions of optimal sagittal and frontal plane alignment. 2. Explanations of how posture is controlled through sensory inputs, muscle activity, and strategies like fixed support and changing support. 3. Analyses of deviations from optimal posture, including positions of the foot, knee, spine, and effects of sitting and lying postures. Factors like age, gender, and occupation are also discussed.

1. • DR. Akshi sanghavi
( MPT in musculoskeletal and sports)
Biomechanics of posture

2. Content
• Definition
• Normal posture
• Static and dynamic posture
• Kinetic and kinematics of posture
• Optimal posture – view in standing (lateral view and anterior posterior view)
• Deviation from optimal alignment
• Analysis of sitting posture
• Analysis of lying posture
• Effects Of age ,gender ,pregnancy, occupation on posture.

3. Definition
• Posture is The attitude assumed by the body either with
support during muscular inactivity or by means of The
coordinated action of many muscles working to maintain
stability.

4. SAGITTAL PLANE ALIGNMENT OF
THE BODY IN NORMAL POSTURE
In erect standing, the body is aligned
approximately so that a line through the
body’s center of mass passes very close to
the ear, slightly anterior to the acromion
process of the scapula, close to the greater
trochanter, slightly anterior to the knee
joint, and anterior to the ankle joint

5. FRONTAL AND TRANSVERSE PLANE ALIGNMENT
IN NORMAL ERECT POSTURE

6. Back view

7. STATIC AND DYNAMIC POSTURE
STATIC POSTURE : THE BODY AND ITS SEGMENTS ARE
ALIGNED AND MAINTAINED IN CERTAIN POSITIONS.
EXAMPLES OF STATIC POSTURES INCLUDE STANDING, SITTING,
LYING, AND KNEELING.
DYNAMIC POSTURE : IN WHICH THE BODY OR ITS SEGMENTS
ARE MOVING—WALKING, RUNNING, JUMPING, THROWING,
AND LIFTING

8. Erect bipedal stance and quadrupedal posture
• Erect bipedal stance gives us
freedom for the upper extremities
• certain disadvantages is increases
the work of the heart; places
increased stress on the vertebral
column, pelvis, and lower
extremities; and reduces stability.
• Small base of support and large
center of gravity
• quadrupedal posture, the body weight
is distributed between the upper and
lower extremities.
• Large base of support and low center
of gravity.

10. Postural control
• person’s ability to maintain stability of the body and body segments in response
to forces.
• ability to maintain stability in the erect standing posture is a skill that the central
nervous system (CNS) learns, using information from passive biomechanical
elements, sensory systems, and muscles.
• Reactive(compensatory) responses occur as reactions to external forces that
displace the body’s CoM. Proactive(anticipatory) responses occur in anticipation
of internally generated destabilizing forces such as raising arms to catch a ball or
bending forward to tie shoes.
• posture depend on the integrity of the CNS, visual system, vestibular system, and
musculoskeletal system.
• depends on information received from receptors located in and around the joints
(in joint capsules, tendons, and ligaments), as well as on the soles of the feet.

11. Absent or altered input and outputs
When inputs are altered or absent, the
control system must respond to
incomplete data, and thus the person’s
posture may be altered and stability
compromised
absence of the normal gravitational
force in weightless conditions during
space flight or decreased sensation in
the lower extremities.
inputs may be disturbed is after injury.
A disturbance in the kinesthetic sense
about the ankle and foot after ankle
sprains has been implicated as a cause
of poor balance or loss of stability
• erect posture may be affected by altered
outputs such as the inability of the
muscles to respond appropriately to
signals from the CNS.
• Muscles of person in peripheral nerve
damage.

12. Muscle synergies
• perturbation is any sudden change in conditions that displaces the body
posture away from equilibrium.
• sensory perturbation might be caused by altering of visual input
• Mechanical perturbation are displacements that involve direct changes in
the relationship of CoM to the BoS. These displacements may be caused by
movements of either body segments or the entir body.
• These responses are synergies or strategies. ( fixed support synergies and
change in support synergies)

13. Fixedsupport synergies are patterns 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 remain fixed on the BoS.
• ankle synergy consists of discrete
bursts of muscle activity on either the
anterior or posterior aspects of the
body that occur in a distal-to-proximal
pattern in response to forward and
backward movements of the support
platform, respectively
• hip synergy consists of discrete bursts
of muscle activity on the side of the
body opposite to the ankle pattern in
a proximal-to-distal pattern of
activation

14. Anterior(forward) movement of the platform

15. Posterior movement of platform

16. Change in support strategies
• include stepping (forward, backward, or sidewise) and grasping (using one’s
hands to grab a bar or other fixed support) in response to shifts in the BoS
• Stepping and grasping differ from fixed-support synergies because
stepping/grasping either from fixed support synergies because stepping
/grasping either moves or enlarges the body’s bos
• maintaining stability in the instance of a large perturbation.

17. head stabilizing strategies
• It is a proactive strategies .
• occur in anticipation of the initiation of internally generated forces caused by
changes in position from sitting to standing.
• used to maintain the head during dynamic tasks such as walking.
• two strategies for maintaining the vertical stability of the head: head
stabilization in space (HSS) and head stabilization on trunk (HST)
• The HSS strategy is a modification of head position in anticipation of
displacements of the body’s CoG.
• The HST strategy is one in which the head and trunk move as a single unit.

18. Kinetics and kinematics of posture
• The external forces that will be considered are 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

19. Inertial and gravitational forces
• erect standing posture, little or no accleration of the body occurs, except that
the body undergoes a constant swaying motion called postural sway or sway
envelope.
• the sway envelope for a normal individual standing with about 4 inches
between the feet can be as large as 12in the sagittal plane and 16 in the frontal
plane
• Gravitational forces act downward from the body’s cog.
• in static erect standing posture The log must fall within The bos .

20. Ground reaction forces
• GRFV is equal in magnitude but
opposite in direction to the
gravitational force in the erect static
standing posture.
• The point of application of the GRFV
is at the body’s CoP.

21. Coincident action lines and external and internal
moments
• Grfv and the log have coincident action lines in the static erect posture
• so that the torques and stresses on body segments are minimized and standing
can be maintained with a minimal amount of energy expenditure.
• When the log passes directly through a joint axis no external gravitational
torque is created around that joint.
• If log passes at a distance from the axis an external gravitational moment is
created.
• It is opposed by a counterbalancing internal moment ( a muscle contraction).
• If log located anterior so gravitational moment will tend to cause anterior
motion.
• If log located posterior so gravitational moment will tend to cause posterior
direction.

22. Optimal posture
• ideal standing posture would be one in which the body segments were
aligned vertically and the LoG passed through all joint axes.
• In an optimal standing posture, the LoG is close to, but not through, most
joint axes.
• Therefore, the external gravitational moments are relatively small and can be
balanced by internal moments generated by passive capsular and
ligamentous tension, passive muscle tension (stiffness), and a small but
continuous amount of muscle activity.

23. Lateral view : optimal alignment in the sagittal
plane.

26. Lateral view : deviation from optimal alignment
• Any change in position or malalignment of one body segment will cause
changes to occur in adjacent segments, as well as changes in other segments
• Large changes from optimal alignment increase stress
• If stresses are maintained over long periods of time, body structures may be
altered
• Shortening of the ligaments will limit normal ROM
• whereas stretching of ligamentous structures will reduce the ligament’s ability
• prolonged stretch of a muscle induces protein synthesis and the production of
additional sarcomeres . The lengthened muscle hypertrophies.
• prolonged shortening reveal that shortening produced by immobilization
appears to accelerate atrophy, and muscles demonstrate a loss of sarcomeres.

27. Foot and toes
•Claw toes
Calluses may develop on the dorsal
aspects of the flexed phalange
deformity reduces the area of the BoS
and, as a result, may increase postural
sway and decrease stability in the
standing position.
Affects all toes(second through fifth)
The drawing of claw toes shows hyperextension at the
metatarsophalangeal joint and flexion of the
interphalangeal joints

28. Hammer toes
• Callosities (painless thickenings of the
epidermis) may be found on pip joints.
• tips of the distal phalanges also may show
callosities as a result of abnormal weight-
bearing
• The flexor muscles are stretched over the MTP
joint and shortened over the PIP joint.
• The extensor muscles are shortened over the
MTP joint and stretched over the PIP joint.
Hammer toes are characterized by hypertension
of the metatarsophalangal and distal
interphalangeal joints and by flexion of the
proximal interphalangeal joints.

29. knee

30. Hyperextended knee posture( genu recurvatum)

32. Excessive anterior pelvic tilt

33. Lordosis
• Lordosis refers to the normal anterior convexity (posterior concavity) of the
curves in the lumbar and cervical region of the spine.
• Compression on the posterior aspects of the vertebrae and the posterior
annulus are increased and tensile forces are increased on the anterior aspects
of the vertebrae and the anterior longitudinal ligaments.

34. Kyphosis
• The term kyphosis refers to the normal sagittal plane posteriorly convex
curves in the thoracic and sacral regions of the vertebral column.
• Sometimes an abnormal increase in the normal posterior convexity may
occur, and this abnormal condition also may be called a kyphosis.
• kyphosis may develop as a result of poor postural habits or ostoporosis.
• two types : dowager’s hump and gibbus deformity

35. Dowager’s hump
Dowager’s hump is found most often
in postmenopausal women who have
osteoporosis.
The anterior aspect of the bodies of a
series of vertebrae collapse as a result
of osteoporotic weakening.
increased compression stress on the
anterior portion of the vertebral body.
Increase in the posterior convexity.
Gibbus deformity
May occur as a result of
tuberculosis ,which causes vertebral
fractures.

36. Forward head posture

38. Deviation from optimal alignment anterior and posterior
view
• Pes planus(flat foot)
• Flaf foot is characterized by a
reduced or absent medial arch.
• rigid flat foot is a structural
deformity that may be hereditary. In
the rigid flat foot, the medial
longitudinal arch is absent in non–
weight-bearing, toe-standing, and
normal weight-bearing situations.
• flexible flat foot, the arch is reduced
during normal weightbearing
situations but reappears during toe-
standing or non–weight-bearing
situations.

39. • talar head is displaced anteriorly,
medially and inferiorly
• causes depression of the navicular
bone.
• Lengthening of the tibialis posterior
muscle.
• If the navicular bone is depressed, it
will lie below the Feiss line and may
even rest on the floor in a severe
extent of flat foot.
• Weight-bearing pronation in the erect
standing posture causes medial
rotation of the tibia and may affect
knee joint function.

40. Pes cavus
• The medial longitudinal arch of the
foot may be unusually high.
• A high arch is called pes cavus .
• It is more stable position of the foot
than is pes planus. The weight borne
on the lateral borders of the foot
• lateral ligaments and the peroneus
longus muscle stretched.
• Cavus foot is not a good shock
absorber.

41. Hallux valgus

42. Genu valgum (knock knee)
• In genu valgum, the mechanical axes
of the lower extremities are displaced
laterally and patella also displaced
laterally.
• Produce pronation of the foot with
stress on the medial longitudinal arch.
• Related changes may occur flat
foot,lateral tibial torsion, lateral
patellar subluxation.
n genu valgum (“knock knee”), the medial aspect
of the knee complex is subjected to tensile stress,
and the lateral aspect is subjected to compressive
stress

43. genu varum(bow leg)
• in which the knees are widely separated
when the feet are together and the
malleoli are touching
• Cortical thickening on the medial
concavity of both the femur and tibia may
be present as a result of the increased
compressive forces
• patellae may be displaced medially.
• cause of genu varum are vitamin D
deficiency, renal rickets, osteochondritis,
or epiphyseal injury.
In genu varum (“bowleg”), the lateral aspect of the knee
complex is subjected to tensile stress, and the medial
aspect of the knee complex is subjected to compressive
stress.

44. Squinting or crossed eye patella
• patella (patella that faces medially) is a
tilted/rotated position of the patella
• in which the superior medial pole faces
medially
• and the inferior pole faces laterally
• increased femoral torsion (excessive femoral
anteversion)61 or medial tibial rotation.
• The Q-angle may be increased in this
condition,
• patella tracking may be adversely affected.

45. Grasshopper eyes patella
• laterally displaced position of the
patella
• in which the patella faces upward
and outward
• An abnormally long patella ligament
may be responsible for the higher
than normal position of the patella
(patella alta).
• Femoral retroversion or lateral tibial
torsion may be responsible for the
rotated position of the patella.
• decrease in the stability of the
patella.

46. Scoliosis
• lateral deviations of a series of
vertebrae from the LoG in one or more
regions of the spine may indicate the
presence of a lateral spinal curvature
in the frontal plane called a scoliosis.
• If one or more of the medial-lateral
structures fails to provide adequate
support, the column will bend to the
side.
• Functinal curve called nonstructural
curves –they Can be reversed if the
cause of the curve is corrrected.
• Structural curve involves changes in
bone and soft tissue structures.
idiopathic scoliosis
• Lateral flexion movement present.
• Compression of vertebral body on
the side of concavity of curve.
• Changes in structure of
intervertebral disc,vertebral bodies,
transverse spinous process,
ligaments and muscles.
• Growth on the compressed
side(concavity) is inhibited or slower
than on the side of the convexity of
the curve.
• Shortening of muscle on concavity
• And stretching of muscle , ligaments
and joint capsule on convexity .

47. 1. Uneven waist angles or difference
in arm to body space and unequal
shoulder height or unequal scapula
levels.
• lateral curvature of the vertebral
column that is convex to the right in
the thoracic region and convex to the
left in the lumbar reg.
• rib hump during forward trunk
flexion.

48. Sitting postures
1. Sitting postures are more complex than standing
postures.
2. The same gravitational moments as in standing
posture must be considered,
3. but, in addition, 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.
In the slouched posture, the LoG is posterior to the
spine and hips, but body weight is being supported by
the back of the chair, and so less muscle activity is
required than in active erect posture .
Sustained slumped postures increase in intradiscal
pressure due to an increase in compressive stress on
anterior annulus and increase in the tensile force on the
posterior annulus (which may cause lead to disc
degeneration).

50. Analysis of lying posturs
• 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 mattresssurfaces include foam, air, gas, water, and
gel.
• Otherpressure-relieving surfaces include movable surfaces,usually powered
by a motor or pump, which can alter-natively inflate and deflate.

51. Gender and elderly
• Postural alignment in elderly people may show a more
flexed posture than in the young adult
• Cervical lordosis increased with increasing age
• Log was located more anteriorly with a loss of lumbar
lordosis and increase kyphosis.
• condition such as osteoporosis may affect posture in
elderly person and lead to kyphosis.
• In kyphosis the anterior trunk flexors muscles shorten
as the posteriorly located trunk extensors lengthen.
• Khyphosis significantly decreased lung volume and
maximal inspiratory pressure in the elderly subjects.
• The rom at the knees,hip,ankle, and trunk may be
restricted because of muscle shortening and disuse
atrophy.
• Elderly person may stand wide bos.
The normal thoracic kyphosis was
greater and the normal lumbar
lordosis less in boys than in girls
both at the beginning

52. Pregnancy
• Weight gain during pregnancy and
increase in weight distribution in the
Breast and abdomen.
• Softening of ligamentous and connective
tissues, especially in the pelvis, sacroiliac
joints, pubic symphyses and abdomen.
• Cog distributed anteriorly.
• increase in lordotic curve in the cervical
and lumbar area.
• Protraction of the shoulder girdle and
hyperextension of the knees.
• Anteriorly pelvic tilting and head become
more posteriorly.
• Many women have backache during
pregnancy.

53. Occupation and recreation
• Bricklayers, surgeon, carpenter and cashiers perform tasks in standing postures.
• Secretaries, accountants, computer operators, receptionists assume sitting posture
for a long time.
• Running, jogging And long distance walking are dynamic postures.
• Different sitting postures and their effects on intradiscal pressures in the lumbar
spine.
• Many back problems are preventable because they result from mechanical stresses
produced by prolonged static postures in the forword stopping or sitting positions
and the repeated lifting of heavy loads.
• Violin,piano ,cello and bass players were frequently affected by back and neck
problems.
• String players experienced shoulder and neck problems caused by maintenance of
abnormal head and neck positions.
• Flute players had shoulder problems associated with maintaining an externally
rotated shoulder position.

54. References
• Joint structure and function author cynthia c. norkin(5th adition )
• Kinesiology the mechanics and pathomechanics of human movement author
carol a. oatis (second adition)
• Orthopedic physical assessment author david J. magee (sixth adition)

55. Thank you