Balance and Stability PDF

Balance and stability From whom is balance important? - Over 30% of individuals who are over the age of 65 fall every year. In approximately half of the cases, the falls are recurrent. This percentage increases to around 40% in individuals aged...

Balance and stability From whom is balance important? - Over 30% of individuals who are over the age of 65 fall every year. In approximately half of the cases, the falls are recurrent. This percentage increases to around 40% in individuals aged 85 years and above. - Fall risk factors: impairment in balance, reduced muscle strength, visual problems, polypharmacy, gait difficulty, depression, functional limits, pain… Skill-related fitness: There are 6 components of physical fitness: - Balance - Speed - Coordination - Power - Agility - Reaction time 1. Neurophysiological aspects Nervous system: Balance is related to the functioning of the nervous system Sensorimotor system: - Integration of neurosensory and neuromuscular processes. - The central nervous system (CNS) receives input from three subsystems: - Visual system - Vestibular system - Somatosensory system  Somatosensory system: - Somatic senses are functions of the nervous system that collect sensory information, but they are not the special senses (sight, hearing, taste, touch, smell, and vestibular sense) It encompasses the information gathered by 3 types of “informers”: 1. Somatic exteroceptors: tactile, nociceptive, and thermal sensitivity 2. Enteroreceptors: baroreceptors and chemoreceptors 3. Proprioception: receptors in muscles, tendons, and ligaments Proprioception: (Introduced in 1906 by Nobel Prize in Medicine Sir Charles Scott Sherrington) Ability to determine: - Position in space - Detect movement (kinesthesia) - Amount of force (muscle tone) Proprioception - mechanoreceptors:  - Neuromuscular spindle They are intrafusal fibers Innervation: - Motor: gamma (y) motor neurons, responsible for contraction - Sensory: type IA or primary, and type II or secondary, providing information about length and the rato of changes Myotatic or stretch reflex: protective against excessive or sudden stretching (e.g., patellar reflex). It also maintains muscle tone. Reciprocal information: the myotatic circuit involves inhibition mediated by 2 neuros, known as reciprocal innervation, which targets the antagonist muscles, causing their relaxation while agonist contract. - Golgi tendon organs: They are located at the muscle-tendon junction and within the tendon. Invitation: - Exclusively sensory through typo IB fibers. - They encode tension Inverse myotatic reflex: the contraction of the muscle reflexively indices its relaxation in response to excessive tension. 2. Definitions and classifications BALANCE Definition: the ability to control equilibrium (either static, kinetic or dynamic) To determine if a body is balanced (in a state of equilibrium), two conditions must be met: - With respect to linear movement: all the forces acting on a body must cancel each other, so the external forces must sum to zero. - With respect to angular movement: all the moment of force acting on the body must sum to zero. In real life, balance must be continuously reestablished by the neuromuscular system An essential feature of all movement is the need to keep the body in stable equilibrium, so that we do not fall over while the body is changing its position. EQUILIBRIUM Definition: a state of zero acceleration where there is no change in the speed or direction of the body Types of equilibrium: - Static: the body is at rest and not in motion - Kinetic: the body is moving in a straight and uniform way, resulting in movement with unchanging speed and direction - Dynamic: inertial forces are involved, with non-uniform movements. The body appears to be unbalanced but does not fall. STABILITY Definition: the ability to remain unchanged, even in the presence of forces that would typically alter the state or condition. Stability has also been described as the property of returning to an initial state after a disturbance. 3. Factors that determine balance and stability MECHANICAL: - Base of support (BS) - Projection of the CG within the BS - Height of the CG - Other mechanical factors PHYSIOLOGICAL: - Vestibular, visual, and somatosensory inputs - Aging - Fatigue - Use of medications, alcohol… PSYCHOLOGICAL AND ENVIRONMENTAL: - Stress, fear… - Central control (CNS) PHYSICAL CONDITION: - Basic physical abilities: strength, endurance… - Complex qualities: coordination and agility - Training of basic physical abilities and complex qualities LINE OF GRAVITY: Gravity’s action line which is visualized as a vertical line projecting downwards from the center of gravity. In the upright position, the line of gravity normally passes through the junctions of the various regions of the vertebral column. - The skull with the cervical vertebrae - The cervical with the thoracic vertebrae - The thoracic with the lumbar vertebrae - The lumbar vertebrae with the sacrum - Posterior to hip and anterior to knee and ankle CENTER OF GRAVITY (CG) An imaginary point where the weight of an object is considered to be concentrated The whole weight of the body, or body segment (such as the forearm), acts vertically downwards through the center of gravity of the body or body segment. It does nor necessarily have to be located within the material of the object In the case of a square block or cylinder in which the mass is symmetrically distributed, the point is at the center of the object. If the distribution of the mass is asymmetrical, as in the limbs of the human body, the CG will be nearer to the larger and heavier end. In the upright standing (in the average body): the CG is a point on the midline, just anterior to the second sacral vertebra in adults - anatomical position (standing). Women - it is located lower than in men – wider pervis and shorter limbs - Distance from the ground – 55-57% of the height. Factors affecting location of the CG: AGE - In newborn: above umbilicus - At 2 years: at the level of the umbilicus - At 5 years: below the level of the umbilicus - In adults: anterior to the second sacral vertebrae. - Affect the location of the CG – it affects body parts’ mass proportion - In newborn, the upper part of the body is heavier than the lower part– the CG is higher than in adults - With advanced age, the C0G becomes lower. Factors affecting location of CG: SEX - The CG is higher in males than in females because of the muscular distribution (in males the upper body is heavier than lower body). - The female pelvis is wider and heavier than the male pelvis Factors affecting location of CG: ADDITION OF WEIGHT - Addition of weight - EX: if a person carries a backpack - CG will move backward - Compensatory mechanism – the person will move his trunk forward to prevent falling Factors affecting location of CG: SUBTRACTION OF WEIGHT - In amputation – CG moves away from the amputated limb towards the healthy side - EX: amputated right leg: the CG will move upward and toward the left side - Artificial limb – its weight should be equal to the weight of the healthy limb – avoid abnormal distribution of the segments weight CENTER OF GRAVITY AND STABILITY Stability can be enhanced by determining the body’s center of gravity and changing its position appropriately. BASE OF SUPPORT (BOS) - The supporting area beneath the body - Includes the points of contact with the supporting surface and the area between them - These points may be body parts (such as feet), or extensions of body parts (Such as crutches or other walking aids) - The upright body is least stable when the feet are parallel and close together (because the BOS is small) - At the feet are moved further apart and the BOD increases, stability increases. HEIGHT OF THE CG RELATIVE TO THE BASE OF SUPPORT A lower height of the CG relative to the same base of support increases balance stability because the force required to create a disturbance also increases. PROJECTION OF THE CG ON THE BASE OF SUPPORT The most stable position is when the CG is projected at the center of the base of support ADDITIONAL MECHANICAL ASPECTS Centripetal force inertia, or linear and angular momentum.  4. Assessment of balance and stability Dynamic and static balance test (practice) A system for assessing both static and dynamic balance. BALANCE EVALUATION SYSTEM TEST (BESTest): It consists of 36 items grouped into 6 systems, organized as follows: Progression variants for static and dynamic balance: COMPUTERIZED SYSTEMS AND WEARABLES: Stabilometry: Analyzes the movement of the center of pressure within the base of support. The less movement of the center of pressure required to perform a task (such as standing, walking, or maintaining an inverted balance), the greater the stability of balance for that task. The center of pressure: the point where the sum of the vertical forces applied to the ground equals zero. To measure it, vertical reaction forces need to be recorded on a force platform. How is stabilometry performed? - In a strictly standardized position. - With a visual reference 0.5 - 2 meters from the subject. Familiarization with the protocol is important. - Record the movement of the center of pressure for 20 - 30 seconds at a frequency of 20 - 50 Hz. - Indicators of balance stability quality relate to the minimal movement of the center of pressure, including: total displacement, anterior.posterior displacement, medial-lateral displacement, swept area, velocity.. Wearable Inertial Sensors: - These sensors consist of linear accelerometers and/or angular velocity sensors (gyroscopes) that can measure leg, arm, and torso motions while individuals perform clinical balance tasks or engage in daily activities. - They offer more sensitive, specific, and responsive balance testing for clinical practice. The 12 weeks proprioception training program in older adults is effective in postural stability, static, and dynamic balance and could lead to an improvement in gait and balance capacity and to a decrease in the risk of falling in adults aged 65 years and older. Berg Balance Test; Tinetti Scale; Romberg Test in static posturography analysis (EPS pressure platform) Inertial Sensors and Depth Camera