NORMAL POSTURAL CONTROL POSTURE AND BALANCE • No universal definition. • Being changing as our knowledge too. • Hierarchical & system theories. • Hierarchical explains postural control as maturation of CNS. • While System theory explains interaction of individual, task . • However the term posture is often used to describe both biomechanical alignment and orientation of the body. POSTURAL CONTROL (PC) • 1. 2. Controlling the body’s position in space, for dual purposes Postural stability – the ability to maintain the body in equilibrium Postural orientation - the ability to maintain an appropriate relationship between the body segments and between the body and the environment for a task POSTURAL ORIENTATION • • 1. 2. 3. Biomechanical alignment and orientation of the body with the environment Vertical alignment of our body – multiple sensory references includes: Gravity – vestibular system Support surface – somatosensory system Relationship of our body to objects in our environment – visual system POSTURAL STABILITY • An object is considered stable when the COM is maintained over its BOS • A point that is at the centre of the total body mass – COM • Determined by finding the weight average of the COM of each body segment • The area of the object that is in contact with the support surface – BOS • Vertical projection of the COM is defined as COG. POSTURAL CONTROL ( by Shumway-Cook & Woollacott,2001) Task Environment Postural control↑ Individual body’s position in space ( Stability & Orientation ) SYSTEMS FOR POSTURAL CONTROL • Perception – integration of sensory information to assess the position and motion of the body in space • Action – ability to generate forces for controlling body position system • Postural control is complex interaction of : 1. MSK System – joint ROM, spinal flexibility, muscle properties, and biomechanical relationships among linked body systems 2. Neural System – motor responses, sensory processes, higher level integrative processes • Postural control requirements vary with the functional task and environment. CURRENT VIEWS ON POSTURAL CONTROL ( by Shumway-Cook & Woollacott,2001) MSK NM Adaptive INT.REP. Postural control↑ Anticipatory Ind.Sensory Sensory POSTURAL CONTROL STRATEGIES • Motor strategies – the organization of movements appropriate for controlling the body’s position in space • Sensory strategies – organize sensory information for postural control • Sensorimotor strategies – reflects the rules for coordinating sensory and motor aspects of postural control MOTOR CONTROL OF QUIET STANCE • 1. 2. Characterized by small amounts of spontaneous postural sway Alignment – minimize the effects of gravitational forces, which tend to pull us off centre Muscle tone – muscle tone and postural tone ALIGNMENT • • a) b) c) d) e) Ideal alignment – more equilibrium and least expenditure of internal energy Perfectly aligned posture – vertical line of gravity falls in the midline between: The mastoid process The point just in front of the shoulder joint The hip joints or just behind A point just in front of the knee joints A point just in front of the ankle joint MUSCLE TONE • The force with which the muscle resists being lengthened – that is its stiffness • Testing of muscle tone • Neural and non-neural contributions • During stance posture the ankle muscles are stretched, activating the stretch reflex – shortening of the muscles which control the forward and backward postural sway POSTURAL TONE • • when we stand in upright position, it is observed that in antigravity muscles the tension is increases than normal, thus counteracting the force of gravity. This increase in tension or activity in antigravity muscle is known as postural tone POSTURAL TONE 1. 2. 3. 4. 5. 6. • Soleus and gastrocnmius Tibialis anterior – backward sway Gluteus medius and tensor fascia latae Iliopsoas - prevent hyper extension of the hip Thoracic erector spine Abdominals (Intermittent) Ideal alignment LIMITS OF STABILITY DURING QUIT STANCE • Depends on: 1. Area of BOS 2. The position of the vertical projection of COM as its relates to the edges of the BOS 3. Height of the COM from the support surface 4. Weight of the mass to be controlled • Perceived limit of stability –the distance a person is willing and able to move without losing balance and taking a step MOTOR STRATEGIES DURING PERTURBED STANCE • Muscle synergies – characteristic pattern of muscle activity – associated with postural movement strategies • Functional coupling of groups of muscles to act together as a unit against constrains is a synergy. • Anterior-posterior stability • Mediolateral stability ANTERIOR-POSTERIOR STABILITY ANKLE STRATEGY • 1. 2. • 1. 2. • Forward sway Gastrocnemius – planter flexion Hamstrings and Paraspinals –maintain the knee and hip in extended position Backward sway Anterior Tibialis – Quadriceps and Abdominals – Toes up and toes down ANTERIOR-POSTERIOR STABILITY HIP STRATEGY • 1. 2. 3. • 1. 2. • Forward sway Surface – narrow beam surface versus flat surface Abdominals Quadriceps Backward sway Extensors of back Hamstrings Used in large and fast perturbations ANTERIOR-POSTERIOR STABILITY STEPPING STRATEGY • When the ankle and hip strategies fails to restore balance the step or hop is used to restore the balance • Instruction to the subjects plays important role • Most of the neurologically intact individuals use a mix of ankle, hip and stepping or hopping strategies • Low velocity movements – ankle strategy • High velocity movements – hip strategy MEDIOLATERAL STABILITY • The alignment of body segments and muscles requires the activation of forces at different joints and in different direction to restore stability • In lower limb very little mediolateral movement is possible at knee and ankle • Hip is the only joint for the recovering of stability in mediolateral direction • Mediolateral control of balance occurs primarily at the hip and trunk rather than at the ankle MEDIOLATERAL STABILITY • • • • • During quiet stance – loading and unloading Hip abductors and adductors Descending response organization Proximal to distal direction The head movements occur in opposite direction to those at the hip and ankle • Thigh muscles –support the antigravity muscles - flexorsunloading, extensors-loading SENSORY MECHANISMS • Before generation of forces, knowledge of position of body in space with respect to gravity and environment is important. Three main sources of this knowledge are; • Visual inputs • Somatosensory input • Vestibular inputs VISUAL INPUTS • Position and movement of head with respect to surrounding objects. • Reference for verticality. • It includes peripheral visual information and foveal information. • Not always accurate about self motion. • Difficulty to differentiate between exocentric and egocentric SOMATOSENSORY INPUT • Position and motion information about the body with reference to supporting surface. • Spindles & GTOs.…..length & tension • Joint receptors….Movt. & stress • Cutaneous i.e. Pacinian corpuscles …vib. Meissners C…….Light touch & vibrations Merkel Discs….Local pressure Ruffini endings…..skin stretch • Flat surface….Horizontal plane • Moveable surface….vertical orientation ???? VESTIBULAR INPUTS • Position and movement of head with respect to gravity & inertial forces. • Gravitational frame of reference for PC. • Semicircular canals.. Angular acceleration esp. in fast head movt. as in slips etc. • Otolioths… linear acceleration and effective in slow head movements as in postural sway. • Head nod & forward bend with trunk???? SOMATOSENSORY STRATEGIES DURING QUIET STANCE • Many studies have proved that: propioception from all parts of body plays an important role in maintenance of PC during quiet stance. Adults tend to rely on somatosensory input while young children rely more heavily on visual inputs. • In perturbations somatosensory inputs dominate over others. SOMATOSENSORY STRATEGIES DURING PERTURBED STANCE • Infants learning to stand rely more on visual inputs during perturbations. • CNS heavily rely on somatosensory inputs when imbalance is caused by rapid displacement of supporting surface. • Vestibular system has only minor role when supporting surface displaced horizontally. • Toes up with eyes open visual and vestibular while with closed eyes mainly SCCs. ANTICIPATORY POSTURAL CONTROL • When CNS pre tunes its sensorimotor information's and experiences in anticipation to a task to be completed. • Preparatory phase….50 m.sec. ahead • Compensatory phase for feed back. • Dancers have shown good anticipatory postural adjustments than non dancers. • Postural adjustments also occur before voluntary movements to minimize potential disturbances.
