Balance and Posture Flashcards
Human vs Animal
Compared to (four legged) animals, humans are precariously balanced.
- Small contact area (base of support) of the feet relative to the rest of the body.
- High position of the center of gravity relative to the ground.
- Necessity of control mechanisms to keep balance.
Center of Gravity (CoG)
Point of application of the resultant of gravitational forces.
In anatomical position, it lies anterior between S1 and S2.
Changes with changing of body and limb position.
Center of Mass (CoM)
Theoretical point (measured/calculated) in relation to which the mass of this body is uniformly distributed. Does not change. CoM and CoG are at the same point in upright position.
Base of Support (BoS)
Refers to the area beneath an object or person that includes every point of contact (e.g. feet, hands, crutches, chair…) it makes with the supporting surface.
The bigger the BoS the better.
Limits of stability
Inverted pendulum rotating around the ankle joint with the intended equilibrium position being a slight forward tilt of the body.
Generates a gravity-driven instability.
What is the role of anti-gravity postural muscles?
To control balance.
Generate torque across joints to:
- Resist the tendency to be over-thrown
- Keep limbs, joints, body segments in proper relationship to one another so that the CoG falls within the BoS.
Erect Bipedal Stance
Body weight is borne exclusively by the two lower extremities.
Allows person to use upper extremities for performance of large and small motor tasks.
Disadvantages of Erect Bipedal Stance
In comparison with quadrupedal posture:
- Increase the work of the heart.
- Places increased stress on the vertebral column, pelvis and lower extremities.
- Reduces stability.
Posture
Stereotypical alignment of body/limb segments.
Good posture refers to a position that requires the least effort to maintain (least amount of muscle contractions), puts the least strain on ligaments, bones and joints.
Static Posture
Body and its segments are aligned and maintained in certain positions.
Sitting, standing or sleeping.
Not moving.
Coordination and interaction of various muscle groups which are working statically to counteract gravity and other forces.
Dynamic Posture
Postures in which the body or its segments are moving.
Walking, running, bending over.
Required to form an efficient basis for movement. Muscles and non-contractile structures have to work to adapt to changing circumstances.
Line of Gravity
Highly variable.
In ideal posture, gravity produces a torque to help maintain the optimal shape of each spinal curvature, allowing to stand easily.
Where does the gravity line fall in the sagittal plane?
- Forward of ankle
- Through or forward of the knee
- Through or behind the hip
- Through or behind the thoracic spine
- Through acromion
- Through or forward of atlanto-occipital
Where does the gravity line fall in the frontal plane?
- Symmetrically between two feet
- Through the umbilicus
- Through the xiphoid process
- Through the chin & nose
- Between the eyes
Anti-Gravity Muscles
- Neck muscles
- M. erector spinae
- Gluteus muscles
- Hamstrings
- Calf muscles, soleus
- Cervical muscles
- Abdominal and deep hip muscles
- Knee extensors, quadriceps femoris
What are the effects of bad posture?
- Misalignment of the musculoskeletal system.
- Increase in pressure on the spine, making it more prone to injury and degeneration.
- Neck, shoulder and back pain.
- Decrease in flexibility.
- Affects how well joints move.
- Affects balance and increases risk of fall.
- Harder to digest.
- Harder to breathe.
Lordosis - Body Segment Alignment
Pelvis anteriorly tilted.
Knees in hyperextension
Ankle joint slightly plantar flexed
Lordosis - Muscles Commonly Elongated and Weak
- Anterior abdominals
- Small muscles of lumbar spine (multifidus, rotators)
- Lower and middle trapezius
- Rhomboids
- Thoracic and cervical erector spinae
- Hyoid muscles
Lordosis - Muscles Commonly Short and Strong
- Lumbar erector spinae
- Hip flexors
- Upper trapezius
- Pectoralis major - minor
- Levator scapulae
- Sternocleidomastoid
- Scalenes
- Suboccipital muscles
Lordosis - Joints Commonly Affected
- Lumbar spine
- Pelvic joints
- Hip joints
- Thoracic spine
- Scapulothoracic joints
- Glenohumeral joints
- Cervical spine
- Atlanto-occipital joints
- Temporomandibular joints
Kyphosis - Body Segment Alignment
- Head held forward with cervical spine hyperextended.
- Scapula may be protracted
- Increased thoracic kyphosis
- Hips flexed, knees hyperextended
- Head is usually most anteriorly placed body segment
Kyphosis - Muscles Commonly Weak and Elongated
- Neck flexors
- Upper and thoracic erector spinae
- External obliques
- If scapula is protracted, middle and lower trapezius
- Rhomboids
Kyphosis - Muscles Commonly Short and Strong
- Neck extensors
- Hip flexors
- If scapula is protracted, serratus anterior, pectoralis major and/or minor, upper trapezius, levator scapulae
- Upper abdominal muscles
- Intercostales
Kyphosis - Joints Commonly Affected
- Thoracic spine
- Scapulothoracic joints
- Glenohumeral joints
Sway Back - Body Segment Alignment
- Long kyphosis with pelvis the most anterior body segment, hip joint moves forwards of posture line (thoracic spine mobile to compensate).
- Lower lumbar area flattens
- Pelvis neutral or in posterior tilt
- Hip and knee joint hyperextended
Sway Back - Muscles Commonly Elongated and Weak
- One joint hip flexors
- External obliques
- Lower thoracic extensors
- Lower abdominals
- Neck flexors
Sway Back - Muscles Commonly Short and Strong
- Hamstrings
- Hip extensors
- Upper fibers of internal obliques
- Internal intercostales
- Low back musculature short but not strong
Sway Back - Joints Commonly Affected
- Lumbar spine
- Thoracic spine
- Cervical spine
- Pelvic joints
- Hip joints
- Scapulothoracic joints
- Glenohumeral joints
- Atlanto-occipital joints
- Temporomandibular joints
Flat Back - Body Segment Alignment
- Loss of lordosis with pelvis in posterior tilt
- Hip and knee joints hyperextended
- Forward head posture with increased flexion to upper thoracic spine
Flat Back - Muscles Commonly Elongated and Weak
- One joint hip flexors
- Lumbar extensors
- Local stabilizers (multifidus, rotatores)
- Scapular protractors
- Anterior intercostales
Flat Back - Muscles Commonly Short and Strong
- Hamstrings
- Abdominals may be strong with back muscles slightly elongated
- Hip extensors
- Scapula retractors
- Thoracic erector spinae
Flat Back - Joints Commonly Affected
- Lumbar spine
- Thoracic spine
- Cervical spine
- Pelvic joints
- Scapulothoracic joints
Scoliosis - Body Segment Alignment
- Rotation of the thoracic cage
- Spine curves to the left or right
- May have single or double curve or one main curve and one or two compensatory curves
- Ribs may protrude to one side and be depressed on the other.
- May have a short leg - pelvis tilted laterally - concave side high
- Shoulder/scapula may drop on concavity side of curve
Scoliosis - Muscles Commonly Elongated and Weak
- Muscles on the convex side
- Hip abductor muscles on the concave side
- Foot pronator muscles on the long side
Scoliosis - Muscles Commonly Short and Strong
- Muscles on concave side
- Hip adductors on convex side
- Foot supinators on short side
Scoliosis - Joints Commonly Affected
- Lumbar spine
- Thoracic spine
- Cervical spine (torticollis)
- Pelvic joints
- Hip joints
- Foot joints
- Scapulothoracic joints
- Glenohumeral joints
- Atlanto-occipital joints
- Temporomandibular joints
Balance
Weight spread equally so that you don’t fall.
Ability to move or remain in a position without losing control or falling.
- Postural control
- Variations of leg muscle length induced by rotations around the ankle joint
Equilibrium
Opposing forces or actions are balanced so that one is not stronger than the other.
Systems Model of Balance
Stability
- Goal task orientation
- Central set
- Environmental organization
- Sensory organization
- Motor coordination
- Musculoskeletal system
Goal Task Orientation
- What is the nature of the activity or task?
- What are the goals or objectives?
Central Set
Readiness of the CNS for an upcoming event based on initial conditions, prior to experiences and expectations.
Automatic Postural Responses
Depends on the goal of maintaining equilibrium.
Depend on the central set, so that they are specific to the condition of support and adapt to prior experiences.
Defined by their postural strategies and postural synergies.
Motor Coordination
Precise behavioral and kinematics description of equilibrium reactions exist for various conditions.
- Postural Strategies
- Postural Synergies
Strategies to Maintain/Restore Balance
Postural Strategies
- Body Kinematics: Fixed support strategies that return body CoM over the BoS. → Ankle and Hip strategies.
- Body Kinetics: Change in support strategies that change the BoS under the falling CoM → Stepping and Reaching strategies.
Ankle Strategy
Body moves as a flexible inverted pendulum.
Used when perturbation is:
- Slow
- Low amplitude
- Firm contact surface, wide and longer than foot
Muscles recruited distal to proximal
Head movements in phase with hips
Hip Strategy
Body exerts torque at the hips to quickly move the body CoM.
Used when:
- Perturbation is fast or large amplitude
- Surface is unstable or shorter than feet.
Muscles recruited proximal to distal.
Head movements out of phase with hips.
Gradual Adaption Strategy
If you have nothing to grab.
Gradual adaption from ankle to hip strategy and vice versa when changing from large surfaces to narrow.
Stepping Strategy
Used to prevent fall.
First attempt is to replace the body CoM to initial position by exerting ankle torque.
Used when perturbations are fast or large amplitude or when other strategies fail.
Increases the BoS, distributing the weight by stepping.
Reaching Strategy
Used to prevent fall if a stable support is available.
Faster than stepping strategy.
Forward bend of the trunk with hip/knee flexion, may progress to squatting position.
CoG lowered.
Musculoskeletal System
- ROM of joints
- Strength/power
- Sensation: pain (flexion/extension reflex), reflexive inhibition.
- Abnormal muscle tone: hypertonia (spasticity), hypotonia. (balance not working well)
Sensory Organization
3 Major systems that control balance: - Visual - Vestibular - Somatosensory/Proprioceptive Activated as feedback control.
Which system is responsible for stability while standing on a firm surface?
Mainly rely on information from the proprioceptive system, followed by vestibular and visual information.
What are the 3 main roles of the vestibular system?
3 main roles:
- Engages a number of reflex pathways that are responsible for making compensatory movements.
- Adjustments in body position.
- Engages pathways that project to the cortex to provide perceptions of gravity and movements.
Information from the vestibular system is processed in the brain and then sent to other organs that need this information such as eyes, joints and muscles.
Vestibular System - Inner ear
The ear is a sensory organ, that picks up sound waves, allowing us to hear.
Found in the inner ear:
- 3 semicircular canals: horizontal (lateral); anterior; posterior.
- 2 otoliths organs: the utricle and the saccule
- The cochlea (mainly auditory system) (vestibular system is in close contact with the auditory system, that does NOT control balance.)
Vestibular System - Semicircular Canals
- Each semicircular canal ends in a space that has small hair cells: ampullae (move when we move).
- Respond to angular acceleration.
- Hair cells send the information to the brain via nerves.
They detect acceleration of our movements.
Vestibular System - Semicircular Ducts
Work in pairs to detect head movements. A turn of the head excites receptors in one ampulla and inhibits receptors in the other.
Vestibular System - Saccule and Utricle
Lie against the walls of the inner ear between the semicircular ducts and the cochlea.
The receptors: maculae are patches of hair cells topped by small, calcium carbonate crystals called otoconia (detect speed of movement).
- Utricle senses horizontal linear acceleration (walking).
- Saccule senses vertical acceleration (falling).
Vestibular System - Otoliths Organs
Found diagonally under the semicircular canals and have similar function. They also have hair cells but there are small crystals on the hair cells.
Vestibulo-Ocular Reflex
- Controls eye movement to stabilize images during eye movements.
- When the head moves in one direction, the eyes move in the other direction.
- Direct link from the inner ear (semicircular canals) to the eyes.
Vestibulocollic Reflex
Vestibular - neck. Stabilizes the head position in relation to the gravity vector.
Stabilizes the head in space during active body movements (locomotion). It is canceled during voluntary head movement as it would oppose intended motion.
Direct link between the vestibular system and neck motoneuron.
What are the two major components of the vestibulocollic reflex?
- Medial vestibulospinal tract (MVST).
- Lateral vestibulospinal tract (LVST).
Which direction of movements are the three semicircular canals responsible for?
- Tilting upwards (right and left anterior canals) and downwards (right and left posterior canals)
- Tilting right (left anterior and posterior canals) or left (right anterior and posterior canals)
- Turning sideways to the left (right lateral canal) or to the right (left lateral canal)
Cervico-Collic Reflex
Neck - Neck. Stabilizes the head position in relation to the trunk.
Acts to keep the head to body relation constant.
Which reflexes closely interact together for the vestibular control of the head orientation in space?
Cervico-collic and vestibulocollic reflexes
Visual System - Retina
Provides info on direction and speed of body sway and orientation in the environment.
Provides advanced info about potentially destabilizing situations.
Enables the precise timing and control of the movement in relation to it’s environment (doing a step when you see the bus arriving).
Oculomotor System
Five distinct eye movement system responsible for voluntary and reflex selection of a visual target:
- Vestibular
- Optokinetic
- Smooth pursuit
- Saccadic
- Vergence
Extraocular muscles control all eye movements: controlled by several brain structures.
Somatosensory/Proprioceptive System
Plays a critical role on movement control by providing inputs to internal models that couple sensory signals and motor commands.
What are the components of the proprioceptive system?
Muscle spindle - Muscle length - Rate of change Golgi Tendon Organs (NTOs) - Monitor tension Joint receptors Cutaneous receptors - Skin receptors
Reflex Arc
A number of sensory motor reflex actions are mediated by the local circuitry within the spinal chord.
- Receptor: detects stimulus
- Sensory neuron: conveys sensory info to the brain or spinal chord
- Interneuron: Relay neuron
- Motoneuron: Conduct the motor info to the periphery
- Effector: Muscle or gland
Sensory Receptor Classification: Stimulus they detect
- Mechanoreceptor (change in movement)
- Thermoreceptor (change in temp.)
- Photoreceptor (change in light)
- Chemoreceptor (change in chemical state)
- Nociceptor (pain)
Sensory Receptor Classification: Body Location
- Exteroceptors (Near the surface of the body, monitor external environment)
- Interoceptors (Deep, monitor internal environment, 99% of receptors in the body)
- Proprioceptors (Monitors the relationship of external and internal environment. Position and movement)
Sensory Receptor Classification: Structural Complexity
- Simple receptors
- Complex receptors
Spinal and Cortical Pathways
Activation of soleus muscle(majorly activated in upright position) during upright standing is the results of spinal and cortical pathway modulation.
Environmental Organization
Nature of contact surface - Texture - Moving or stationary? Nature of the surroundings - Regulatory features of the environment
Sensory Reweighting
How much of each sensory system will be activated when environment is changing.
Important mechanism for changing relative contributions made by the different sensory systems for postural control.
Important for maintaining stability when moving from one context to another.
Percentage of sensory systems active on a firm surface
Proprioceptive 70%
Vestibular 20%
Vision 10%
Changes in sensory systems on an unstable surface
Increase in vision and vestibular sensory weighting
Decrease dependence on proprioceptive input
