Balance refers to the ability to maintain the line of gravity, which is, the vertical line from center of mass of a body within the base of support with minimal postural sway.

Sway is the horizontal movement of the center of gravity even when a person is standing still. 

A certain amount of sway occurs due to small perturbations within the body.

Such perturbations include: breathing, shifting body weight from one foot to the other or from forefoot to rearfoot, or from external triggers like visual distortions, floor translations.

An increase in sway is an indicator of decreased sensorimotor control.

Maintaining balance requires coordination of input from multiple sensory systems including the vestibular, somatosensory, and visual systems.

Vestibular system: includes sense organs that regulate equilibrium : directional information as it relates to head position-internal gravitational, linear, and angular acceleration.

Somatosensory system: senses of proprioception and kinesthesia of joints; information from skin and joints via pressure and vibratory senses, spatial position and movement relative to the support surface, movement and position of different body parts relative to each other

Visual system: Refers to verticality of body and head motion; spatial location relative to objects.

These senses must detect changes of spatial orientation with respect to the base of support, regardless of whether the body moves or the base is altered. 

There are environmental factors that can affect balance such as light conditions, floor surface changes, alcohol, drugs, and ear infection.

There are balance impairments associated with aging that include age-related decline in the ability of the vestibular, somatosensory, and visual systems, to receive and integrate sensory information.

The elderly are at an increased risk of falls: one in three adults aged 65 and over will fall each year.

In an individual standing quietly upright, the limit of stability is defined as the amount of postural sway at which balance is lost and corrective action is required.

Deficits in postural balance is related to the control of medial-lateral stability and an increased risk of falling. 

To remain balanced, a person standing must be able to keep the vertical projection of their center of mass within their base of support, resulting in little medial-lateral or anterior-posterior sway. 

The most common residual disability post ankle sprain is instability along with body sway. 

Mechanical instability factors include  insufficient stabilizing structures and mobility that exceed physiological limits. 

Functional instability is seen with recurrent sprains or a feeling of giving way at the ankle.

Nearly 40% of patients with ankle sprains suffer from instability and an increase in body sway.

Ankle injuries cause a proprioceptive deficit and impaired postural control. 

Patients with  muscular weakness, instability, and decreased postural control are more susceptible to ankle injury than those with better postural control.

Balance can be severely affected with neurological conditions. 

People who suffer a stroke or spinal cord injury can have impaired balance.

Impaired balance is strongly associated with future function and recovery after a stroke, and is the strongest predictor of falls.

Balance is severely affected is Parkinson’s disease patients, related to a reduced limit of stability and an impaired production of anticipatory motor strategies and abnormal calibration.

Balance can also be negatively affected through fatigue in the musculature surrounding the ankles, knees, and hips. 

Muscle fatigue around the hips, gluteals and lumbar extensors, and knees have an effect on postural stability.

Muscle fatigue leads to a decreased ability to contract with the correct amount of force or accuracy.

With muscle fatigue proprioception and kinesthetic feedback from joints are altered so that conscious joint awareness may be negatively affected.

Balance is a key predictor of recovery and is required in many activities of daily living, and is  included therapy treatment plans by physiotherapists and occupational therapists when dealing with geriatrics, patients with neurological conditions, or others for whom balance training has been determined to be beneficial.

Balance training in stroke patients commonly used and proven to be effective for this population include sitting or standing balance practice with various progressions including reaching, variations in base of support, use of tilt boards, gait training varying speed, and stair climbing exercises.

To improve balance perturbation training is used, as an external force applied to a person’s center of mass in an attempt to move it from the base of support.

The type of training should be determined on the nature and severity of the stroke, stage of recovery, and the patient’s abilities and impairments after the stroke.

The elderly, children with neuromuscular diseases, and those with motor deficits such as chronic ankle instability with balance training have improvements in postural sway and improved one-legged stance balance.

Balance training benefits can be measured by typical quantitative outcomes as centre of pressure (CoP), postural sway, and static/dynamic balance: measured by the subject’s ability to maintain a set body position while undergoing some type of instability.

Higher level of physical activity reduces morbidity and mortality along with risk of fall up to 30% to 50%.

Some types of exercise of gait, balance, co-ordination and functional tasks, strengthening exercise improve clinical balance outcomes in older people, and are seemingly safe.

Aerobic exercise with resistance exercise improves balance ability.

Functional tests of balance focus on maintenance of both static and dynamic balance, involve perturbation/change of center of mass during quiet stance.

Standardized tests of balance allow allied assessment on individual’s postural control: 

Romberg Test: used to determine proprioceptive contributions to upright balance: Subject remains in quiet standing while eyes are open. 

 Sharpened Romberg’s test: Subjects have their arms crossed, feet together and eyes closed, decreasing decreases the base of support, raises the subject’s center of mass, and prevents them from using their arms to help balance.

Functional Reach Test: measures the maximal distance one can reach forward beyond arm’s length while maintaining feet planted in a standing position.

Berg Balance Scale: measures static and dynamic balance abilities using functional tasks commonly performed in everyday life.

Berg Balance Scale is one of the most commonly used assessment tool throughout stroke rehabilitation, and found it to be a sound measure of balance impairment in patients following a stroke.

Performance-Oriented Mobility Assessment (POMA): measures both static and dynamic balance using tasks testing balance and gait.[

Timed Up and Go Test: measures dynamic balance and mobility.

Balance Efficacy Scale: self-report measure that examines an individual’s confidence while performing daily tasks with or without assistance.

Star Excursion Test: A dynamic balance test that measures single stance maximal reach in multiple directions.

Balance Evaluation Systems Test (BESTest): Tests for 6 unique balance control methods to create a specialized rehabilitation protocol by identifying specific balance deficits.

The Mini-Balance Evaluation Systems Test (Mini-BESTest): Is a short form of the Balance Evaluation System Test that is used widely in both clinical practice and research. It includes 14 items of dynamic balance task, divided in to four subcomponents: anticipatory postural adjustments, reactive postural control, sensory orientation and dynamic gait. 

It is  considered a standard balance measure.

BESS: The BESS (Balance Error Scoring System) is a commonly used way to assess balance. 

The BESS tests three separate stances (double leg, single leg, tandem) on two different surfaces (firm surface and medium density foam) for a total of six tests. 

Each test is 20 seconds long.

The entire time of the assessment approximately 5–7 minutes. 

The first stance is the double leg stance. 

Standing on a firm surface with feet side by side with hands on hips and eyes closed. 

The second stance is the single leg stance. In this stance standing on their non-dominant foot on a firm surface with hands on hips and eyes closed. 

The third stance is the tandem stance. The participant stands heel to toe on a firm surface with hands on hips and eyes closed. 

The fourth, fifth, and sixth stances repeat in order stances one, two, and three except the participant performs these stances on a medium density foam surface. 

Quantitative computerized assessments of balance that measure the center of pressure terrestrial locomotion (CoP), the reaction vector of center of mass on the ground’s path length for a specified duration.

A minimal CoP path length is suggestive of good balance. 

Fatigue, causing central nervous system (CNS) dysfunction, can indirectly result in the inability to remain upright: Parkinson’s disease, multiple sclerosis.

Older adults have more body sway with all testing conditions.

Older adults demonstrate shorter functional reach and larger body sway path lengths. 

Height influences body sway in that as height increases, functional reach typically decreases. 

Specific types of exercise for gait, balance, co-ordination and functional tasks; strengthening exercises; 3D exercises [Tai Chi] can help improve balance in older adults. 

Balance is mostly an automatic process, however, voluntary control is common. 

Active control usually takes place where balance is compromised, and  can have the counter-intuitive effect of increasing postural sway during basic activities such as standing. 

Conscious control may result in over-correcting an instability and inadvertently disrupt relatively automatic control processes.

Concentration on an external task promotes the use of more automatic control processes.

Supra-postural tasks are activities that rely on postural control while completing another behavioral goal, such as walking or creating a text message while standing upright. 

Having postural stability permits the achievement of other activities.

Postural control acts to minimize the amount of effort required while accomplishing the supra-postural tasks.

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