What is Balance?
Balance is the ability to maintain the body’s center of mass over its base of support. Balance is achieved and maintained by a complex set of sensorimotor control systems (Figure 1) that include sensory input from vision (sight), proprioception (touch), and the vestibular system (motion, equilibrium, spatial orientation); integration of that sensory input; and motor output to the eye and body muscles . When any of these systems is injured or deficient, balance can markedly be affected.
Figure 1 - Mechanisms of balance
Its interlacing feedback mechanisms can be disrupted by damage to one or more components through injury, disease, or the aging process. Impaired balance can be accompanied by other symptoms such as dizziness, vertigo, vision problems, nausea, fatigue, and concentration difficulties.
The complexity of the human balance system creates challenges in diagnosing and treating the underlying cause of imbalance. The crucial integration of information obtained through the vestibular, visual, and proprioceptive systems means that disorders affecting an individual system can markedly disrupt a person’s normal sense of balance. Vestibular dysfunction as a cause of imbalance offers a particularly intricate challenge because of the vestibular system’s interaction with cognitive functioning, and the degree of influence it has on the control of eye movements and posture.
The functional goals of the balance system includes :
Maintenance of a specific postural alignment, such as sitting or standing,
Facilitation of voluntary movement, such as the movement transitions between posture
Reactions that recover equilibrium to external disturbances, such as a trip, slip, or push.
It is important to remember that intact balance control is required not only to maintain postural stability but also to assure safe mobility-related activities during daily life, such as standing while performing manual tasks, rising from a chair, walking and turning.
Importance of balance assessment
Several conditions like stroke, Parkinson’s disease, multiple sclerosis, cerebral palsy, vestibular dysfunctions, knee and foot lesions, traumatic brain injury, among many others will affect balance. The impact of balance disorders is enormous, both for affected individuals and for the society at large. Thus, it is important to have tools such as posturography to help health professionals identify if there is a balance problem and the specific nature and/or the cause of the problem.
Figure 2 - Balance Assessment.
The main value of a posturography exam is the objective information it provides, allowing to assess the patient :
Different sensory systems involved in balance (vestibular, visual and somatosensory);
Changes of automatic and voluntary motor responses;
Deviations from the center of gravity;
Changes of limits of stability.
Several manipulations can be introduced to static posturography to render the balancing task more challenging, such as reducing the size of the base of support, decreasing visual feedback (eyes closed), decreasing proprioceptive feedback (foam surface), or applying a secondary task while subjects maintain their balance. For example, if a patient has difficulty in maintaining balance with eyes closes in unstable surface indicates a sensory pattern of vestibular dysfunction. There are also other patterns than can be found such as surface dependence or combined visual-vestibular deficit. Thus, posturography can help understand the pathophysiological mechanism in patients with balance disorders .
There are several studies about the use of posturography instruments in different pathologies. For example, Guntram et al. , studied the difference of body sway in elderly people and patients with Parkinson’s disease and detected significant differences of sway parameters in eyes closed examinations. Reid et al.  also used posturography to assess the incidence of large-fiber peripheral neuropathy by comparing the results with conventional electromyography (EMG) results. This study showed abnormal sway patterns only in patients who had EMG abnormalities consistent with the pathology, and differed significantly from the control subjects’ results.
In Balaguer García R, et al. study , it was found that posturography with static and dynamic tests could discriminate between normal and peripheral vestibular disorder subjects, providing complementary information to classic tests like vestibulo-ocular reflex to better understand the functional status of patients with instability.
Bigelow KE and Berme N  evaluated 150 elderly people, categorized according to their history of falling during the last year. They found that the eyes closed comfortable stance testing condition and its associated model best differentiated recurrent fallers from nonrecurrent fallers.
It is important to point out that it can also help health professionals to guide and evaluate the effectiveness and efficiency of rehabilitation programs to maximize treatment of the balance disorder. As well as establish baselines that are reproducible, practical and reliable, allowing monitoring of the patient's evolution.
To sum up, patients with balance impairment require optimal medical attention, for both diagnostic and therapeutic reasons:
Diagnostic purposes – Differential diagnosis in patients with falls or balance impairment, and early detection of subjects at risk of falling;
Therapeutic purposes – Development of optimal treatment strategies tailored to individual needs, and objective documentation of therapeutic efficacy;
Long-term purpose – Improved understanding of underlying pathophysiology, as a basis for renewed treatment strategies.
Importance of balance training
There are many aspects to consider when developing therapy programs for people with balance impairments. As balance control can be considered a fundamental motor skill learned by the central nervous system, postural control strategies can become more efficient and effective with training and practice . In recent years, evidence in support of postural rehabilitation has been increasing and a growing number of studies have shown that training performed by means of postural platforms with visual feedback is more effective than traditional physiotherapy approaches [2-4].
Balance training (Figure 3) can benefit a wide range of patients, such as recovering from an orthopedic operation or an incident such as a stroke or other neurological event, where balance skills must be re-learned to help a patient regain a former level of competence. Balance training can also benefit elderly patients with gradually weaker balance skills, by teaching them new methods of compensation so that they can maintain their level of independence and limit their risk of falling as they age .
Figure 3 - Balance Training.
Visual biofeedback provides additional information about the COP position, thus having a stabilizing effect with improved balance . Its addition to a balance training program improves the results obtained and its use translates into improved parameters such as postural sway, load alternation, orthostatism reaction time and Berg Balance Scale .
Barclay-Goddard et al.  reviewed the use of force platforms in balance training in stroke patients. According to these authors, training on a force platform, using visual or visual and auditory feedback, improved support symmetry. Mraz et al.  evaluated the effects of a rehabilitation program, including exercises with visual feedback, in individuals with vertigo syndrome. After carrying out the program, which lasted one month, the authors verified a decrease in postural sway and an improvement in visual-motor coordination. Moreover, there have been several studies about the use of therapeutical games in rehabilitation, demonstrating significant balance improvements in elderly people [8-9] and patients with acquired brain injury .
So, balance training with biofeedback helps patients meet a number of goals that physiotherapists traditionally set for their patients. These goals include:
Correct distribution and balance of weight during standing and walking;
Bringing a limb to full use following an orthopedic operation (particularly ankle training);
Shortened reaction time;
Tracking a moving object;
Correctly and easily transferring weight from one weight-bearing limb to another;
Suppressing synkinetic movements;
Attention focus during balance.
PhysioSensing (balance device system- figure 4) includes exercises that which are planned to help patients meet each of these goals. In addition, the exercises can be used to help patient develop compensatory mechanisms that assist in maintaining balance, including plasticity, internal models, learning of limits, and sensory input decisions. Using this system, the clinician can plan exercises to help his patients meet these aims and improve their day-to-day functioning.
PhysioSensing is indicated to assist physiotherapy activities, physical and vestibular rehabilitation, and neurorehabilitation, especially in the early rehabilitation of stroke and neuromusculoskeletal conditions associated to lower limbs and gait rehabilitation.
Figure 4 - PhysioSensing Balance and Training device.
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