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Posture
- 2. Normal posture Analyzing different postures Kinetics and Kinematics of posture
- 3. • It is a measure of mechanical efficiency of muscles, balance and of neuromuscular coordination. • It is considered as the relative arrangement of parts of the body. It changes with the positions and movements of the body throughout life and throughout the day. • It is the attitude which is assumed by body parts to maintain stability and balance with minimum effort and least strain during supportive and non supportive positions.
- 6. Static posture The body and its segments are aligned and maintained in certain positions Dynamic posture •Refers to postures in which the body or its segments are moving
- 7. Static or dynamic •Refers to a person’s ability to maintain stability of the body and body segments in response to forces that threaten to disturb the body’s equilibrium •Reactive (compensatory) responses •Proactive (anticipatory) responses
- 8. Depend on –somatosensory –Visual system –Vestibular system
- 9. Dominant sensory system Provides fast input Reports information – Self-to-(supporting) surface – Relation of one limb/segment to another Components – Muscle spindle » Muscle length » Rate of change – GTOs (NTOs) » Monitor tension – Joint receptors » Mechanoreceptors – Cutaneous receptors
- 10. Reports information – Self-to-(supporting) surface – Head position » Keep visual gaze parallel with horizon Subject to distortion Components – Eye and visual tracts – Thalamic nuclei – Visual cortex » Projections to parietal and temporal lobes
- 11. Not under conscious control Assesses movements of head and body relative to gravity and the horizon (with visual system) Resolves inter-sensory system conflicts Gaze stabilization Components – Cerebellum – Projections to: » Brain stem » Ear
- 12. Sensory-Motor Integration Somatosensory Vestibular Visual Eye Movements Postural Movements 10 Processor 20 Processor Cerebellum Motoneurons Sensory Input Processing Motor Response
- 13. For any particular task many different combinations of muscles may be activated to complete the task A normally functioning CNS selects the appropriate combination of muscles to complete the task on the basis of an analysis of sensory inputs
- 14. Patterns of muscle activity in which the Base of support(Bos) remains fixed during the perturbation . Ankle synergy Hip synergy
- 15. 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
- 17. 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
- 19. Stepping (forward, backward, sidewise) •Grasping In response to shift in the BoS.
- 20. Used to prevent a fall Used when perturbations are fast or large amplitude -or- when other strategies fail BOS moves to “catch up with” BOS
- 21. 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 Strategies –Head stabilization in space –Head stabilization on trunk
- 22. External forces ◦ Inertia ◦ Gravity ◦ Ground reaction forces(GRF) Internal forces ◦ Muscle activity ◦ Passive tension in ligaments, tendons, joint capsules, soft tissue structures
- 23. Inertial and Gravitational forces –Body undergoes a constant swaying motion: postural sway or sway envelope
- 24. Ground reaction forces –Resultant force that represents the magnitude and direction of loading applied to one or both feet
- 25. Ground Reaction force
- 26. Centre of Pressure (COP) ◦ Located in the foot in uni-lateral stance and between the feet in bilateral standing postures.
- 27. OPTIMAL POSTURE
- 28. The LoG is close to most joint axis The external gravitational moments are relatively small and can be balanced by internal moments generated by ◦ Passive capsular tension ◦ Ligamentous tension ◦ Passive muscle tension (stiffness) ◦ Small amount of muscle activity
- 30. From anterior or posterior View: The line of gravity passes from the vertex through S2 to a point between the two feet in the base of support
- 31. From lateral View: The line of Gravity passes through: a. Vertex. b. Mastoid process( behind). c. Anterior to the axis of flexion and extension of the neck. d. Acromion Process ( bisecting) e. Body of C1,C6,T11, L5, S1 ( it passes posterior to the axes of rotation of the cervical and lumbar vertebrae and anterior to thoracic vertebrae. f. Via or behind the axis of the hip joint. g. Anterior to the axis of the knee joint. h. 5 cm anterior to lateral malleolus.
- 33. Sagittal plane alignment and analysis Ankle ◦ Neutral position ◦ The LoG passes slightly anterior to the lateral malleolus
- 34. Sagittal plane alignment and analysis Knee ◦ Full extension ◦ LoG passes anterior to the midline of the knee and posterior to the patella (LoG just anterior to the knee axis)
- 35. Sagittal plane alignment and analysis Hip and pelvis ◦ Hip in neutral position, pelvis is level with no anterior or posterior tilt ◦ LoG passes slightly posterior to the axis of the hip joint, through the greater trochanter
- 36. Sagittal plane alignment and analysis •Lumbosacral joints –LoG passes through the body of the fifth lumbar vertebra, close to the axis of rotation of the lumbosacral joint
- 37. Sagittal plane alignment and analysis Sacroiliac joints ◦ LoG passes slightly anterior to the sacroiliac joints ◦ Tends to cause the anterior superior portion of the sacrum to rotate anteriorly and inferiorly, whereas the posterior inferior portion tends to move posteriorly and superiorly
- 38. Sagittal plane alignment and analysis The vertebral column –Optimal position of LoG is through the midline of the trunk
- 39. Sagittal plane alignment and analysis Head –LoG passes slightly anterior to the transverse axis of rotation for flexion and extension of the head
- 40. Postural problems may originate in any part of the body May cause increase stresses and strains throughout the musculoskeletal system •Compensatory postures: postures that represent an attempt to either improve function or normalize appearance
- 41. Foot and toes –Claw toes: hyperextension of MTP combined with flexion of PIP and DIP –Hammer toes: hyperextension of the MTP joint, flexion of the PIP joint and hyperextension of the PIP joint
- 42. Knee –Knee flexion contractures –Hyperextended knee posture (genu recurvatum) Pelvis –Excessive anterior pelvic tilt
- 43. Vertebral column –Lordosis and kyphosis Dowager’s hump Gibbus (deformity) Head –Forward head posture head is positioned anteriorly and the normal anterior cervical convexity is increased with the apex of the lordotic cervical curve at a considerable distance from the LoG in comparison with optimal posture.
- 45. LoG bisects the body into symmetrical halves •When postural alignment is optimal, little or no muscle activity is required to maintain stability.
- 46. Foot and toes ◦ Pes planus (flat foot) Rigid flat foot Flexible flat foot ◦ Pes Cavus Knee ◦ Genu valgum ◦ Genu varum ◦ Squinting or cross-eyed patella (patella that face medially) ◦ Grasshopper-eyes patella
- 47. Vertebral column –Scoliosis • Two classifications Functional Structural
- 48. Goal: to attain a stable alignment of the body that can be maintained with the least expenditure of energy and the least stress on body structures Active erect sitting position: ◦ an unsupported posture in which a person attempts to sit up as straight as possible
- 49. Muscle activity Interdiskal pressures
- 51. Seat interface pressures: ◦ the pressure caused by contact forces between the person’s body and the seat Individuals with physical disabilities have significantly higher seat interface pressures than do people without such disabilities
- 52. Interdiskal pressures ◦ Are less in lying postures than in standing and sitting postures
- 53. Elements – Firm mattress for support – Not too many pillows - Maybe none – Lying flat on back may decrease lordosis – Hook-lying may preserve lordosis – Side-lying may be more comfortable
- 54. Surface interface pressures –Uniform pressure distribution over the entire available surface is desirable to prevent sections of increased pressure over certain areas
- 55. Age –Infants and children –Elderly Pregnancy •Occupation and recreation –“overuse injuries’
- 56. What are the different synergies? In erect posture where will the line of gravity be? What are the different optimal postures?
- 57. Levangie K, & Norkin C., 2005, Joint structure and function, a comprehensive analysis •Hamill J, & Knutzen K., 2003, Biomechanical basis of human movement
Notas do Editor
- The erect bipedal stance is unique to humans. Erect bipedal stance gives us freedom for the upper extremities, but in comparison with the quadrupedal posture, erects stance has certain disadvantages. Erect bipedal stance increases the work of the heart; places increased stress on the vertebral column, pelvis and lower extremities; reduces stability. The human species’ base of support (BoS), definded by an area bounded posteriorly by the tips of the heels and anteriorly by a line joining the tips of the toes, is considerably smaller than the quadrupedal BoS. The human’s center of gravity (CoG) is the point where the mass of the body is centered and will be referred to as the center of mass (CoM). The position of the CoM is not fixed and changes in different postures.
- The ability to maintain stability in the erect standing posture is a skill that the central nervous system learns, using information from passive biomechanical elements, sensory systems and muscles. The CNS interprets and organizes inputs from the various structures and systems and selects responses on the basis of past experience and the goal of the response. 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.
- Postural control 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. The CNS must be able to detect and predict instability and must be able to respond to all of this input with appropriate output to maintain the equilibrium of the body. Furthermore, the joints in the musculoskeletal system must have a range of motion (ROM) that is adequate for responding to specific tasks, and the muscles must be able to respond with appropriate speeds and forces. When inputs are altered or absent, the control system must respond to incomplete or distorted data and thus the person’s posture may be altered and stability compromised
- For any particular task such as standing on a moving bus, standing on a ladder or standing on one leg many different combinations of muscles may be activated to complete the task.
- 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.
- The change in support strategies include stepping or grasping in response to shifts in the BoS. Stepping and grasping differ from fixed-support synergies because stepping/grasping moves or enlarges the body’s BoS so that it remains under the body’s CoM. Change in support synergies are the only synergies that are successful in maintaining stability in the instance of a large perturbation. Comparisons of the stepping strategies used by the young and old show that the younger subjects have a tendency to take only one step, whereas the elderly subjects have a tendency to take multiple steps that are shorter and of less height than those of their younger counterparts. However, no differences are apparent in the speed at which the young and the elderly initiate the change in support strategy.
- The head stabilization in space strategy is a modification of head position in anticipation of displacements of the body’s CoG. The anticipatory adjustments to head position are independent of trunk motion. The head stabilization on trunk strategy is one in which the head and trunk move as a single unit.
- Examining the effects of both external and internal forces on the body in the standing posture. The sum of all of the external and internal forces and torques acting on the body and its segments must be equal to zero for the body to be in equilibrium. Stability is maintained by keeping the body’s CoM over the BoS and the head in a position that permits gaze to be appropriately oriented.
- The extent of the sway envelope for a normal individual standing with about 4 inches between the feet can be as large as 12 degrees in the sagittal plane and 16 degrees in the frontal plane.
- GRF has three components, vertical force (y- axis) and two force components horizontal, medial lateral rotation (x-axis), anterior posterior direction (z-axis). Ground reaction force vector is equal in magnitude but opposite in direction to the gravitational force in the erect static standing posture.
- COP is like COG where the force is considered to act, although the body surface that is in contact with the ground may have forces acting over a large portion of its surface area. to evaluate the effects of attentional demands and perturbations on standing posture. Much of the research on postural control uses the pattern of displacements of the COP.
- In the neutral ankle position , there are no ligamentous checks capable of counterbalancing the external dorsiflexion moment; therefore, activation of the plantarflexors creates the internal plantarflexion moment that is necessary to prevent forward motion of the tibia. The soleus muscle contracts and exerts a posterior pull on the tibia and in this way is able to oppose the dorsiflexion moment. If the force that the muscle can exert is less than the gravitational moment, the tibia will move the ankle into dorsiflexion and the soleus muscle will undergo an eccentric contraction while trying to oppose the forward motion of the tibia.
- The anterior location of the gravitational line in relation to the knee joint axis creates an external extension moment. The counterbalancing internal flexion moment created by passive tension in the posterior joint capsule and associated ligaments is usually sufficient to balance the gravitational moment and prevent knee hyperextension. Activity of the soleus muscle may augment the gravitational extension moment at the knee through its posterior pull on the tibia as it acts at the ankle joint. In contrast, activity of the gastrocnemius muscle may tend to oppose the gravitational extension moment because the muscle crosses the knee posterior to the knee joint axis.
- In a level pelvis position, lines connecting the symphysis pubis and the anterior-superior iliac spines are vertical, and the lines connecting the ASIS’s and PSIS’s are horizontal. It is possible that the iliopsoas is acting to create an internal flexion moment at the hip to prevent hip hyperextension. If the gravitational extension moment at the hip were allowed to act without muscular balance, hip hyperextension ultimately would be checked by passive tension in the iliofemoral, pubofemoral and ischiofemoral ligaments.
- Passive tension in the sacrospinous and sacrotuberous ligaments provides the internal moment that counterbalances the gravitational torque by preventing upward tilting of the lower end of the sacrum.
- EMG studies have shown that the longissimus dorsi, rotatores and neck extensor muscles exhibit intermittent electrical activity during normal standing. This evidence suggests that ligamentous structures and passive muscle tension are unable to provide enough force to oppose all external gravitational moments acting around the joint axes of the upper vertebral column. In the lumbar region, where minimal muscle activity appears to occur, passive tension in the trunk flexors apparently are sufficient to balance the external gravitational extension moment.
- This external flexion moment, which tends to tilt the head forward, may be counteracted by internal moments generated by tension in the ligament nuchae, tectorial membrane and posterior aspect of the zygapophyseal joint capsules and by activity of the capital extensors.
- Large changes from optimal alignment increase stress or increase force per unit area on body structures. If stresses are maintained over long periods of time, body structures may be altered. Muscles may lose sarcomeres if held in shortened positions for extended periods. Such adaptive shortening may accentuate and perpetuate the abnormal posture, as well as prevent full ROM from occurring. Muscles may add sarcomeres if maintainede in a lengthened position, and as a consequence, the muscle length-tension relationship will be altered. Shortening of the ligaments will limit normal ROM, whereas stretching of ligamentous structures will reduce the ligament’s ability to provide sufficient tension to stabilize and protect the joints. Prolonged weight-bearing stresses on the joint surfaces increase cartilage deformation and may interfere with the nutrition of cartilage. As a result the joint surfaces may become susceptible to early degenerative changes.
- Claw toes: The abnormal distribution of weight may result in callus formation under the heads of the metatarsals or under the end of the distal phalanx. Sometimes the proximal phalanx may subluxate dorsally on the metatarsal head. Calluses may develop on the dorsal aspects of the flexed phalanges from constant rubbing on the inside of shoes. In essence, this deformity reduces the area of BoS. Suggested etiologies: the restrictive effect of shoes, a cavus-type foot, muscular imbalance, ineffectiveness of intrinsic footmuscles, neuromuscular disorders and age-related deficiencies in the plantar structures. Hammer toes: Callosities may be found on the superior surfaces of the PIP joints over the heads of the first phalanges as a result of pressure from the shoes. 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.
- Knee flexion contractures: the LoG passes posteriorly to the knee joint axes. The posterior location of the LoG creates an external flexion moment at the knees that must be balanced by an internal extension moment created by activity of the 4ceps muscle in order to maintain the erect position. The necessery 4ceps force rises. The increase in muscle activity needed to maintain a flexed knee posture subjects the tibiofemoral and patellofemoral joints to greater-than-normal compressive stress and can lead to fatigue of the 4ceps and other muscles if the posture is maintained for a prolonged period. Other consequences of a flexed knee erect standing posture are related to the ankle and hip. Because knee flexion in the upright stance is accompanied by hip flexion and ankle dorsiflexion, the location of LoG also will be altered in relation to these joint axes, creating an external flexion moment. The additional muscle activity subjects the hip and ankle joints to greater-than-normal compression stress. Overall, the increased need for 4ceps, gastrocnemius, soleus and hip extensor activity appears to substantially increase the energy requirements for stance. Genu recurvatum: The LoG is located considerably anterior to the knee joint axis. This causes an increase in the external extensor moment acting at the knee, which tends to increase the extent of hyperextension and puts the posterior joint capsule under considerable tension stress. The anterior portion of the knee joint surfaces on th femoral condyles and anterior portion of the tibial plateaus will be subject to abnormal compression and therefore are subject to degenerative changes of the cartilaginous joint surfaces. The length-tension relationship of the anterior and posterior muscles also may be altered, and the muscles may not be able to provide the force necessary to provide adequate joint stability and mobility. Excessive anterior pelvic tilt: may increase lumbar lordotic curve. The LoG is at a greater distance from the lumbar joint axes than is optimal and the extension moment in the lumbar spine is increased. The posterior convexity of the thoracic curve increases and becomes kypothic to balance the lordotic lumbar curve and maintain the head over the sacrum. Similarly, the anterior convexity of the cervical curve increases to bring the head back over the sacrum. Increases in the anterior convexity of the lumbar curve during erect standing increases the compressive forces on the posterior annuli and may adversely affect the nutrition of the posterior portion of the intervertebral disks. Also, excessive compressive force may be applied to the zygapophyseal joints
- The kyphosis may develop as a compensation for an increase in the normal lumbar curve, or the kyphosis may develop as a result of poor postural habits or osteoporosis. Dowager’s hump is an easily recognizable excessively kyphotic condition that 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. Diseases such as tuberculosis or ankylosing spondylosis may cause abnormal increases in the posterior convexity of the thoracic region. A gibbus or humpback deformity may occur as a result of tuberculosis, which causes vertebral fractures. A forward head posture is one in which the head is positioned anteriorly and the normal anterior cervical convexity is increased with the apex of the lordotic cervical curve at a considerable distance from the LoG in comparison with optimal posture. The constant assumption of a forward head posture causes abnormal compression on the posterior zygappphyseal joints and posterior portions of the intervertebral disks and narrowing of the intervertebral foramina in the lordotic areas of the cervical region. The cervical extensor muscles may become ischemic because of the constant isometric contraction required to counteract the larger than normal external flexion moment and maintain the head in its forward position. In the forward head posture, the scapulae may rotate medially, a thoracic kyphosis may develop, the thoracic cavity may be diminished, vital capacity can be reduced, and overal body height may be shortened.
- A Gibbus or Humpback occur as a result of tuberculosis, it forms a sharp posterior angulation in the upper thoracic vertebra column. Dowager’s hump is excessively kyphotic condition found in mostly postmenopausal women who have osteoporosis.
- The LoG bisects the face into equal halves. The eyes, clavicles and shoulders should be level. Scapulae should be parallel and equidistant from the LoG. ASIS and PSIS should lie on a line parallel to the ground, as well as being equidistant from the LoG. The joint axis of the hip, knee and ankle are equidistant from the LoG.
- When one malleolus appears more prominent or lower than the other and calcaneal eversion is present, it is possible that a common foot problem know as pes planus, or flat foot, may be present. Flat foot, which is characterized by a reduced or absent medial arch is a structural deformity that may be either rigid or flexible. A rigid flat foot is a structural deformity that may be hereditary. In the rigid flat foot, the medial longitudinal arch is absent in non-weightbearing, toestanding and normal weight-bearing situations. In the flexible flat foot, the arch is reduced during normal weight-bearing situations but reappears during toestanding or non-weight-bearing situations.
- Scoliosis: consistent 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. There are two classification of curves: functional curves and structural curves. Functional curves can be reversed. Although scoliosis is identified as a lateral curvature of the spine in the frontal plane, the deformity also occurs in the transverse (as vertebrae rotate) and sagittal planes (as the column buckles). Deformities can interfere with breathing and the function of other internal organs, as well as being cosmetically unacceptable.
- The LoG passes close to the joint axes of the head and spine in active erect sitting posture. In the slumped posture, the LoG is more anterior to the joint axes of the cervical, thoracic and lumbar spines than it is in either active or relaxed erect sitting. Therefore we would expect that more muscle activity would be required in the slumped posture than in the other sitting postures. In contrast, maintaining an active erect posture requires not only a greater number of trunk muscles but also an increased level of activity in some of these muscles. It is postulated that the passive tissues were able to assume the load in the relaxed erect and slumped postures and that was why the thoracic erector spinae muscles ceased their activity.
- Individuals with physical disabilities have significantly higher seat interface pressures than do people without such disabilities. Peak seat interference pressures were found to be highest in thin elderly persons who had the least amount of soft tissue over the ischiae. These individuals probably had a smaller contact area with more concentration of pressure than did individuals with a greater body mass with increased surface contact area and better pressure distribution.
- The erect standing posture in infancy and early childhood differs somewhat from postural alignment in adults, but by the time a child reaches the age of 10 or 11 years, postural alignment in the erect standing position should be similar to adult alignment. Postural alignment in elderly people may show a more flexed posture than in young adult. Conditions such as osteoporosis weakens the vertebral bodies and makes them liable to fractures. Pregnancy: The location of the woman’s CoG changes because of the increase in weight and its distribution anteriorly. Consequently, postural changes in pregnancy include an increase in lorditic curves in the cervical and lumbar areas of the vertebral column., protraction of the shoulder girdle and hyperextension of the knees. Occupation and recreation: Many of the injuries sustained during both occupational and recreational activities belong to the category of ‘overuse injuries’. This type of injury is caused by repetitive stress that exceeds the physiologic limits of the tissues. Muscles, ligaments and tendons are especially vulnerable to the effects of repetitive tensile forces, whereas bones and cartilage are susceptible to injury from the application of excessive compressive forces. Each occupational and recreational activity requires a detailed biomechanical analysis of the specific postures involved to determine how abnormal and excessive stresses can be relieved.