Postural Imbalance in the Elderly: Main Aspects

The aging of the population is an unprecedented world phenomenon. Numerous physiological changes occur with aging, and one of the most common situations is postural imbalance and, consequently, the occurrence of falls. Balancing is the process of controlling the body ’ s center of mass with respect to its base of support and depends on the integration of sensory systems (visual, vestibular, and somatosensory) with the central nervous system (CNS). Each system is prone to deterioration with advancing age and is influenced by age-related diseases and use of some types of medications and polypharmacy. As with any good clinical evaluation, a detailed history and a thorough physical examination are essential to evaluate postural balance. The evaluation of balance must be done with tests that are quick and with relatively little equipment and training. The improvement of postural balance can be done in many ways, and exercises are a type of this treatment and can be done with video games or a treadmill, for example.


Aging of population
The aging of the population is an unprecedented world phenomenon. The projections of the World Health Organization indicate that by 2050, all ages will increase by 35%, people aged 65-84 will increase by 164%, older people aged 85-99 will increase by 301% and centenarians will grow by 746% [1].
Increasing longevity also contributes to an aging population. Globally, life expectancy at birth is projected to increase from 69 years in 2005-2010 to 76 years in 2045-2050 and to 82 years in 2095-2100 [1] (Figures 1 and 2).
Physiological changes are observed with aging, increasing the risks of developing chronic diseases and dependence care. Auditory, visual, and movement problems may be present in people 60 years or older. In addition, some conditions such as dementia, heart disease, stroke, respiratory disorders, diabetes, and musculoskeletal conditions (osteoarthritis and back pain) are more frequent in this age group [2].
One of the most common situations for the elderly is postural imbalance and, consequently, the occurrence of falls, representing a significant health problem in older adults. Each year, approximately 30% of community-dwelling older people fall at least once and 10-20% fall twice or more [3]. The incidence among institutionalized older people is even higher, with a mean percentage of residents who fall each year of over 40% [4].

Postural balance
Balancing is the process of controlling the body's center of mass with respect to its base of support, whether in a static or dynamic situation. It depends on the integration of sensory systems with the CNS. Sensory information from somatosensory, visual, and vestibular systems must be integrated to interpret complex sensory environments. Each system interacts with each other to maintain balance in a closed loop, with an interrelation of cause and effect. When the sensory environment is changed, the CNS needs to re-weigh the contribution of each of the senses in postural balance. In an environment with good lighting and a firm surface, the contribution of somatosensory information is 70%, the visual information is 10%, and the vestibular information is 20% [5].
Each system is prone to deterioration with advancing age, and this is influenced by age-related diseases and use of some types of medications, in addition to polypharmacy [6]. Systems can partially compensate for each other's deterioration. Failing compensation strategies may eventually result in impaired balance, which may result in falls [7].

Vision and postural balance
The role of central and peripheral vision information in the control of movements and posture was examined in some studies [8,9]. These authors suggested that peripheral vision is used for postural control and most particularly for stabilization of fore-aft sways, while the central vision is more often used for foot trajectory planning, targeting, obstacle avoidance, and stabilization of lateral sways.
Visual impairment is an important health problem and a major cause of injury in the elderly. Cataract, glaucoma, age-related macular degeneration, and diabetic retinopathy are the most common diseases related to the elderly and can interfere with the postural balance.

Cataract
Cataract, affecting mainly visual acuity and contrast sensitivity, contributes to about 50% of visual impairments in the elderly [10,11]. The consequences include decreased ability to perform activities of daily living (such as reading, watching television, driving, and interacting socially), depression, increased number of falls, and increased mortality [10,12]. The impact on patients is comparable with that of major systemic conditions including stroke, diabetes, and arthritis. In a study in patients with cataract, Pasma et al. found a higher proprioceptive weight compared with healthy elderly participants, which means that the elderly with cataract rely more on their proprioceptive information [7].

Glaucoma
Glaucoma is a progressive optic neuropathy characterized by degeneration of retinal ganglion cells and their axons with consequent vision loss and blindness. This condition leads to a characteristic reduction in the visual field (VF), with good central visual acuity. Previous studies have reported a higher risk of falling in patients with glaucoma compared to normal subjects [13][14][15]. In the study by Black et al., a cohort of glaucoma subjects was examined to assess body displacement of the trunk and the results showed that the worse the visual field defect, the greater the body sway [16].

Age-related macular degeneration
Age-related macular degeneration (AMD) is a disease that affects the macula (central vision), altering the accuracy of vision necessary for "direct" and fine activities, and may interfere with activities of daily living [17].
Wood et al. studied postural balance in older adults with AMD and showed that diminution of contrast sensitivity and visual field loss lead to postural instability and mobility difficulties in these patients [18]. Chatard et al., studying 10 elderly unilateral AMD subjects, 10 elderly bilateral AMD subjects, and 10 healthy age-matched control subjects, showed that bilateral AMD subjects had a surface area and an antero-posterior displacement of the CoP higher than healthy elderly. Unilateral AMD subjects had more antero-posterior displacement of the CoP than healthy elderly [19]. The authors conclude that because of aging, AMD subjects could have poor postural adaptive mechanisms which increase instability and risk of falls.

Diabetic retinopathy
Diabetic retinopathy (DR) is a common and potentially blinding microvascular complication of diabetes [20]. In a study, Gupta et al. found that diabetes per se was not a risk factor for falls. However, the authors found an association between diabetic patients with DR and risk of falling [20], suggesting a relation between DR and postural balance.
The greater tendency to fall in patients with mild-to-moderate DR can be explained by a reduction in the components of the visual function system, such as contrast, sensitivity, stereo acuity, and color perception [21,22]. Figure 3 summarizes the normal vision and main eye disorders that can interfere with the postural balance described above.
Thus, it is important to evaluate visual function when we propose to work with postural balance in the elderly.

Vestibular system and postural balance
Through its sensory functions, the vestibular system detects the position and movement of the head in space relative to gravity, and helps to stabilize vision and balance [23].
The vestibular system has structures similar to miniaturized accelerometers, which report continuous information to the cerebral cortex, cerebellum, and somatic sensory cortices on the movements and position of the head and body. The vestibular nuclei make connections with structures of the brainstem and cerebellum and also innervate the motor neurons that control extraocular, cervical, and postural muscles [23] ( Figure 4).
Impaired function of the vestibular system causes vertigo, loss of balance, and loss of gaze fixation during movement, often accompanied by dizziness and nausea [24].
Vestibular dysfunction is typically characterized by vertigo (i.e., an illusory sense of motion) and imbalance owing to disturbances in gaze and postural stability [25], which can culminate in falls [26].
So, the evaluation of the vestibular system is indispensable when the patients have a impaired balance control.

Somatosensory system and postural balance
People rely primarily on the proprioceptive and cutaneous input to maintain normal quiet stance and to safely accomplish the majority of activities of daily living [27].
The proprioceptive information depends on muscle spindles, the Golgi tendon organ (GTO), and articular receptors. The first provide the nervous system with information about the muscle's length and velocity of contraction, thus contributing to the individual's ability to discern joint movement and position sense [28]. Besides, the muscle spindles provide afferent feedback that translates stimuli to appropriate reflexive and voluntary movements. The GTO relays information about tensile forces, and is sensitive to very slight changes [28], and when it is activated, the afferent neuron synapses in the spinal cord interneurons, which inhibit the muscle alpha motoneuron, resulting in decreased tension in muscle and tendon. Articular or joint proprioceptors respond to mechanical deformation of the joint capsule and ligaments.
On a slippery or dry floor surface, people show different gait parameters, including step length, required coefficient of friction, and heel contact velocity, evidencing the importance of the sensorimotor system in balance control [29].
Sensorimotor impairments occur with aging and are believed to contribute to the increased likelihood of imbalance and falling [30]. Damage to joint and muscular Some diseases can affect muscles and joints. Studies have shown that, in patients with knee osteoarthritis (AO), postural balance is impaired due to reduced quadriceps function and decreased proprioception [31,32]. Among elderly individuals, the prevalence of knee OA is approximately 12.2%, with a higher prevalence in women (14.9%) than in men (8.7%) [33].
Patients with neuromuscular diseases (NMDs), usually characterized by muscle weakness, appear to fall regularly. Aging causes a loss of muscle mass with a preferential decline in type II fibers [34], besides decrements in force production, power, specific tension, and fatigability [35], increasing the risk of falls.

Key points
• Elderly population is increasing.
• Postural imbalance and falling are serious problems faced by the older population.
• Postural control is based on the interpretation by central nervous system of convergent sensory information from somatosensory, vestibular, and visual systems.
• Impairments in these systems lead directly to functional loss, such as the inability to walk safely, to climb stairs, and dress independently, increasing the risk of falls.
3. Approach to the patient with a balance problem

Physical examination
As with any good clinical evaluation, a detailed history and a thorough physical examination are essential. As the postural balance depends on several systems, it is essential to evaluate the visual system, the vestibular and auditory system, and the sensorimotor system.

Functional performance tests
A comprehensive assessment of balance is important for both diagnostic and therapeutic reasons in clinical practice.
The tests can be divided between single-task measures and multiple-task measures [36]. These tests often can be done very quickly and with relatively little equipment and training.

Single-leg stance test
The single leg-stance test (SLS) is simple, has high reliability and low cost, and is widely used for diagnosis and follow-up of patients in research and clinical settings. In this test, the participant remains supported on one leg, with arms resting on the hips, and the time (in seconds) that the patient remains in the position without unbalance is verified [37]. Decreased eyes-open SLS time is associated with an increased risk for falls [38].

Functional reach test
The functional reach test (FRT) is an easy and inexpensive test in which the patient flexes the trunk, extending the arms horizontally and keeping the feet in contact with the ground. The score is obtained by measuring the distance between the initial and the final positions of the fingertip [39]. Displacements less than 15 cm indicate postural balance problems and increased risk of falls [40].

Gait speed test
The gait speed test gives an easy, inexpensive, reliable measure of functional capacity [41], with high interrater and test-retest reliability [42]; does not require laboratory equipment; is not limited to a specific health care discipline [43]; and may be done quickly in clinical settings. The test may vary according to the pace (usual or maximal speed), whether static or moving start, and the distance walked (ranging from 4 to 500 m) [44].

Berg Balance Scale
The Berg Balance Scale (BBS) consists of a battery of 14 tasks common to the activities of daily living, which quantitatively evaluate the risk of falls, through observations undertaken by the examiner [45]. The score on the test ranges from 0 to 56 and the performance on each task is measured on a five-point scale ranging from 0 to 4 (0 = unable to perform, 4 = independent). Scores of 48 or less indicate inability to walk independently and safely in activities of daily living and, consequently, increased risk of falls [46].

Short physical performance battery
The short physical performance battery (SPPB) is designed to measure functional status and physical performance, assessing walking speed, standing balance, and sitto-stand performance [47]. The scores range from 0 (worst performance) to 12 (best performance). In a study, Veronese et al. demonstrated that SPPB scores ≤6 are associated with a higher fall rate in old people [48].

Timed up and go
The Timed up and go (TUG) test was developed in 1991 [49]. The test consists of finding the time the patient takes to get up from a chair (height about 46 cm), walk the distance of 3 m at a comfortable and safe step, turn around and go back to the chair, and sit down again. The subject wears his regular footwear and uses his customary walking aid (cane or walker) if necessary [49]. A faster time indicates a better functional performance [50].

Key points
• A good clinical evaluation, a detailed history, and a thorough physical examination are essential to evaluate postural balance.
• The tests can be divided between single-task and multiple-task measures.
• Assessment of balance is important for both diagnostic and therapeutic reasons in clinical practice.

Figure 5.
Recommendations to guide the use of exercise for falls prevention.

Improvement of the postural balance
Falls are a public health problem. The risk of falling increases with age for many reasons, for example overall weakness and frailty, balance problems, cognitive problems, vision problems, some medications and polypharmacy, acute illness, and other environmental hazards. Because of this, multifactorial interventions should include an initial assessment of modifiable risk factors for falls and subsequent customized interventions for each patient based on issues identified in the initial assessment.
One type of treatment to improve balance is physical exercise. Figure 5 presents a summary of best practice recommendations to use for improving postural balance and, consequently, fall prevention.

Types of exercises
Any physical exercise that overloads the balance systems without putting the patient at risk is recommended. It is possible, for example, to make a training circuit, with different stimuli for the elderly [51]. In the circuit, exercises such as one-legged support (both sides), gait on unstable surface, tandem gait, among others can be done, always increasing the level of difficulty.
Another possibility is to join two modalities of exercises: video games and muscle strengthening, for example. In a study, Prata and Scheicher found improvement in fear of falling and in mobility after 12 weeks of video game and muscle strength training in older women with a history of falls [52].

Video games
Postural balance training involving new technologies can promote more challenging situations for the elderly, increasing patient motivation and adherence to the program [53]. The use of video games provides immediate visual feedback, allowing users to make changes in motion according to the situations of the games and thus to develop strategies to restore and/or maintain postural balance, and may therefore be effective for the prevention of falls [54]. Carvalho et al. showed an increase in gait speed and a decrease in the TUG time in elderly female fallers after 12 weeks of training (two sessions per week) with commercialized games of Wii Fit by Nintendo ® in sync with the Wii Balance Board ® [55]. Three different games were used for postural balance training: Penguin Slide, where the participants had to catch fish while balanced on a piece of ice by shifting their weight from side to side; Table Tilt, where participants move their bodies in various directions to put balls into holes; and Tightrope, where participants walk on a tightrope with several vertical jumps to avoid obstacles.

Treadmill exercise
In the last decade, the use of the treadmill in the rehabilitation of gait in Parkinson's disease patients, stroke patients, and cerebral palsy (CP) patients has been studied. Some studies explain the reasons for improving postural balance patterns with treadmill training. One of them explains that treadmill training has the capacity to promote motor re-learning and, consequently, improve locomotor capacity during walking [56]. It has also been suggested that training, through repetitive movements generated by the treadmill, activates locomotor patterns of functional movements, sensory inputs, and circuits of the central nervous system [57]. In addition, it has been hypothesized that repetitive movements associated with cutaneous and proprioceptive impulses may induce activation of central movement patterns and, in the long term, potentiate the motor cortex, facilitating motor learning [58].
Toole et al. and Frenkel-Toledo et al. showed an improvement in the gait and balance in Parkinson's patients that participated in a six-week treadmill walking program [59,60]. Herman et al. showed an enhancement in the gait rhythmicity and several improvements in motor signs, the latter remaining significantly better 4 weeks after the training was stopped [61].
Training on a treadmill to fight the stroke-related disabilities resulted in valuable results: fatigue resistance [62], endurance performance improvement [63], and the development of motor function [64]. A study in chronic non-ambulatory hemiparetic subjects revealed that partial body weight-supported treadmill training was superior to conventional physiotherapy with regard to restoration of gait and improvement of ground walking velocity [65]. In this study, during one 30-min session of treadmill training, patients could practice up to 1000 gait cycles as compared with a median of less than 50 gait cycles during one regular physiotherapy session.
Bjornson et al. studied the effect of short-burst interval locomotor treadmill training on walking capacity and performance in cerebral palsy and concluded that this training may improve short-term walking capacity and performance [66]. In another study, Mattern-Baxter et al. concluded that home-based treadmill training accelerates the attainment of walking skills and decreases the amount of support used for walking in young children with CP [67].
In healthy elderly with falls history, there are few studies that evaluated the responses of the postural balance with the treadmill training. Dorfman et al. found that after 6 weeks of treadmill plus dual-task training program, elderly fallers demonstrated improved scores on tests of mobility, functional performance tasks, and cognition [68]. In another study, van Ooijen et al., using a treadmill training with visual context, found improvement in walking ability and reduced risk of falls and fear of falling in older adults with a recent fall-related hip fracture [69].

Key points
• Any physical exercise that overloads the balance systems without putting the patient at risk is recommended.
• Postural balance training involving new technologies can promote more challenging situations for the elderly, increasing patient motivation and adherence to the program.
• Treadmill training is another form of exercise to challenge the postural control system.

Conclusion
It is necessary to consider the various facets of the postural balance system when a patient presents a problem related to this. Evaluating these facets is important in prescribing the correct treatment for each situation. There are many types of training that can improve postural balance. Physical exercises, when performed with a moderate or high challenge to the balance system, are a type of treatment that can help reduce the risk of falls in the elderly.