Original Editor - The Open Physio project.
- 1 Introduction
- 2 Variation in Terminologies
- 3 Balance systems
- 4 Static and Dynamic Balance
- 5 Management of balance in specific conditions
- 6 References
IntroductionBase of support (BOS). It can also be described as the ability to maintain equilibrium, where equilibrium can be defined as any condition in which all acting forces are cancelled by eachother resulting in a stable balanced system.
Variation in Terminologies
In literature the balance term has been used synonymously with 
- Postural Control
- Postural Stability
The following systems provides input regarding the body's equilibrium and thus maintains balance.
- Somatosensory / Proprioceptive System
- Vestibular System
- Visual System
The Central Nervous System receives feedback about the body orientation from these three main sensory systems and integrates this sensory feedback and subsequently generates a corrective, stabilizing torque by selectively activating muscles. In normal condition, healthy subjects rely 70% on somatosensory information and 20% Vestibular & 10% on Vision on firm surface but change to 60% vestibular information, 30% Vision & 10% somatosensory on unstable surface.
Proprioceptive information from spino-cerebellar pathways, processed unconsciously in the cerebellum, are required to control postural balance.  Proprioceptive information has the shortest time delays, with monosynaptic pathways that can process information as quickly as 40–50 ms and hence the major contributor for postural control in normal conditions.
The vestibular system generates compensatory responses to head motion via:
- Postural responses (Vestibulo Spinal Reflex) - keep the body upright and prevent falls when the body is unexpectedly knocked off balance.
- Ocular-motor responses (Vestibulo Ocular Reflex) - allows the eyes to remain steadily focused while the head is in motion.
- Visceral responses (Vestibulo Colic Reflex) - help keep the head and neck centred, steady, and upright on the shoulders.
To achieve this the vestibular system measures head rotation and head acceleration through semicircular canals and otolith organs (utricule and sacule)
For non impaired individuals under nornal conditions the contribution of visual system to postural control is partially redundant as the visual information has the longer time delays as long as 150-200 ms. Friedrich et al. (2007)  observed that adults with visual disorders were able to adapt peripheral, vestibular, somatosensoric perception and cerebellar processing to compensate their visual information deficit and to provide good postural control. In addition, Peterka (2002), found that adults with bilateral vestibular deficits can enhance their visual and proprioceptive information even more than healthy adults in order to reach an effective postural stability. The influence of moving visual fields on postural stability depends on the characteristics of the visual environment, and of the support surface, including the size of the base of support, its rigidity or compliance.
Static and Dynamic Balance
Balance can be classified in to :
- Static Balance: it is the ability to maintain the body in some fixed posture.  Static balance is the ability to maintain postural stability and orientation with centre of mass over the base of support and body at rest.
- Dynamic Balance: Defining dynamic postural stability is more challenging, Dynamic balance is the ability to transfer the vertical projection of the centre of gravity around the supporting base of support.  Dynamic balance is the ability to maintain postural stability and orientation with centre of mass over the base of support while the body parts are in motion.
The mechanisms involved in static balance were best summarized by Bannister . He noted that normal standing required:
- Sufficient power in the muscles of the lower limbs and trunk to maintain the body erect.
- Normal postural sensibility to convey information concerning position.
- Normal impulses from the vestibular labyrinth concerning position.
- A central coordinating mechanism, the chief part of which is the vermis of the cerebellum.
- The activity of higher centers concerned in the willed maintenance of posture.
With this mechanisms the dynamic balance requirements can be inferred as:
- Sufficient power in the muscles of the body to maintain movement and stability.
- Normal postural sensibility to convey information regarding movement.
- Normal impulses from the vestibular system and visual system concering movement and environment.
- Central co ordinating mechanism including cerebellum and basal ganglia
- The activity of higher centers concerned in the willed/ involuntary maintenance of movement and stability.
Correlation between Static and Dynamic Balance
A study by Sell TC (2012) examined the relationship and differences between static and dynamic postural stability in healthy, physically active adults. Static postural stability was measured by a single-leg standing task and dynamic postural stability was measured by a single-leg landing task using the Dynamic Postural Stability Index.The author concludes that there was a lack of a correlation between static and dynamic measures. However, the increase in difficulty during dynamic measures indicates differences in the type and magnitude of challenge imposed by the different postural stability tasks.
The lack of correlation between the two different conditions is likely due to the challenge imposed on the systems necessary for maintenance of postural stability. Maintenance of postural stability during both dynamic and static conditions involves establishing an equilibrium between destabilizing and stabilizing forces and requires sensory information derived from vision, the vestibular systems, and somatosensory feedback.
Management of balance in specific conditions
Parkinson’s disease (PD) is a progressive neurodegenerative disease. It’s often characterized by tremor, bradykinesia, postural instability and rigidity. Most frequently, patients have gait impairments, difficulty in linking movements together smoothly and episodes of freezing. The sum of these problems, together with balance disturbances lead to an increased incidence of falls. 
The physiotherapist is a member of the multidisciplinary team, with the purpose of maximising functional ability and minimising secondary complications. Physiotherapy for Parkinson’s disease focuses on: transfers, posture, upper limb function, balance, gait, and physical capacity. The therapist uses cueing strategies, cognitive movement strategies and exercise to maintain or increase independence, safety, and quality of life. Sensory cueing strategies such as auditory, tactile, and visual cues have often been used to help walking in PD.  
Cognitive movement strategies
Cognitive movement strategies are used to improve transfers. Complex and automatic activities are divided into separate elements consisting of relatively simple movement components. By doing this, the person has to think consciously about his movements. Try to avoid dual tasking during complex automatic ADL. Furthermore, the movement or activity will be practiced and rehearsed in the mind. It is important that movements are not performed automatically; performance has to be consciously controlled 
Example: Sit to stand 
- Hands on chair
- Place feet correctly
- Move forward
- Flex trunk
- Rise up from chair
The performance of automatic and repetitive movements of patients with PD is disturbed as a result of fundamental problems of internal control. That’s why cues are used to complete or replace this reduced internal control.
Cues can be generated internally or externally. Rhythmical recurring cues are given as a continuous rhythmical stimulus, which can serve as a control mechanism for walking.  
- Auditory (moves on music/ walkman, singing, counting,...)
- Visual (p follows another person, walks over stripes on the floor or over stripes he projects to himself with a laserpen,...)
- Tactile(p taps his hip or leg)
The physical therapeutic intervention goals apply to the phase addressed: 
Early phase - patients have no or little limitations. Goals of the therapeutic intervention are:
- Prevention of inactivity
- Prevention of fear to move/to fall
- Preserving/ improving physical capacity
Mid phase - more severe symptoms; performance of activities become restricted, problems with balance and an increased risk of falls
- Reaching and grasping
Late phase - patients are confined to a wheelchair or bed. The treatment goal in this phase is to preserve vital functions and to prevent complications, such as pressure sores and contractures.
Balance training can also be used in the elderly. Falls of elderly, due to poor balance, have important clinical and economical costs and intervention. For this reason it is interesting to search for possibilities to reduce these costs, such as the use of balance training.
In 2011 weak evidence has been found for the effectiveness of several exercises in improving clinical balance outcomes in elderly:
- Co-ordination and functional tasks
- Strengthening exercise
- But evidence for the effect of computerized balance programs or vibration plates is insufficient.
To keep the therapy adherence up it is best to look for an approach with a ‘fun factor’. Some examples:
- Music-based multitask exercise program - basic exercises consisted of walking in time to the music and responding to changes in the music’s rhythmic patterns. Exercises involved a wide range of movements and challenged the balance control system mainly by requiring multidirectional weight shifting, walk-and-turn sequences, and exaggerated upper body movements when walking and standing.
- Balance training using a virtual-reality system - in contrast to the review of 2011, in 2013 it was found an effective method to train the balance in older fallers. This method is intended to complete, not replace, other fall prevention programs.
- Tai chi - tai chi has been proven to be an economic and effective way for training balance in older people. 
To ameliorate balance in elderly it isn’t enough to just follow a conventional exercise intervention (including muscle strengthening, stretching and aerobic exercises, and health education). Besides this it is better to also include static and dynamic balance exercises.
Examples of static balance exercises: squats, two-leg stance and one leg stance.
Examples of dynamic exercises: jogging end to end, sideways walking or running with crossovers, forward walking or running in a zigzag line, backward walking or running in zigzag line.Nevertheless to improve balance core strength training is an important element. The benefit is this therapy can be both given in a group setting or in individual fall preventive interventions.
- Susan B O sullivan, Leslie G Portnry. Physical Rehabilitation :Sixth Edition. Philadelphia: FA Davis. 2014.
- Peterka RJ. Sensorimotor integration in human postural control. J Neurophysiol 88: 1097–1118, 2002.
- Cynthia Lions,Emmanuel Bui Quoc,Sylvette Wiener-Vacher,and Maria P. Bucci1:Postural control in strabismic children: importance of proprioceptive information:Front Physiol. 2014; 5: 156.
- Hwang S, Agada P, Kiemel T, Jeka JJ (2014) Dynamic Reweighting of Three Modalities for Sensor Fusion. PLoS ONE 9(1): e88132. doi:10.1371/journal.pone.0088132
- Friedrich M, Grein HJ, Wicher C, Schuetze J, Mueller A, Lauenroth A, Hottenrott K, Schwesig R:Influence of pathologic and simulated visual dysfunctions on the postural system.:Exp Brain Res. 2008 Mar; 186(2):305-14.
- Nicoleta Bugnariu and Joyce Fung;Aging and selective sensorimotor strategies in the regulation of upright balance:J Neuroengineering Rehabil. 2007; 4: 19
- Bannister R: Brain's Clinical Neurology, ed 3. New York, NY,Oxford University Press, Inc, 1969, pp 51-54, 102
- GOLDIE PA, BACH TM, EVANS OM. Force platform measures for evaluating postural control: fckLRReliability and validity. Arch Phys Med Rehabil. 1989; 70:510-517
- Sell TC. An examination, correlation, and comparison of static and dynamic measures of postural stability in healthy, physically active adults. Phys Ther Sport. 2012;13:80–86.
- Mehrholz J, Friis R et al, Treadmill training for patients with Parkinson’s disease (Review), The Cochrane Collaboration, 2010 http://cdn.physioblasts.org/f/public/1282390662_223_FT5630_park.pdf
- Deane KHO, Jones D, Physiotherapy for parkinson’s disease: a comparison of techniques, Cochrane Database of Systematic Reviews, 2001 http://www.ncbi.nlm.nih.gov/pubmed/11687029 fckLRlevel of evidence: 1
- Tomlinson CL, Patel S, Physiotherapy versus placebo or no intervention in Parkinson’s disease, Cochrane Database Syst Rev. 2012 Jul 11 http://www.ncbi.nlm.nih.gov/pubmed/22786482 level of evidence: 1
- S.H.J. Keus H.J.M. Hendriks et al, KNGF: Ziekte van Parkinson Praktijkrichtlijn, jaargang 114, nummer 3, 2004 fckLRlevel of evidence: 2
- Dr. Samyra Keus, Evidence-based guidelines for physiotherapy in Parkinson’s disease, ParkinsonNet, 16 May 2012 http://www.appde.eu/pdfs/Keus_ParkinsonNet_Physiotherapy%20Guidelines.pdf fckLRlevel of evidence: 2
- Anat Mirelman, Talia Herman et al, Audio-Biofeedback training for posture and balance in Patients with Parkinson’s disease, J Neuroeng Rehabil. 2011 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3142211/ fckLRlevel of evidence: 2
- Newell D. et al., Changes in gait and balance parameters in elderly subjects attending an 8-week supervised Pilates programme, J Bodyw Mov Ther, 2012fckLRLevel of evidence: 3
- Howe T.E. et al., Exercise for improving balance in older people, Cochrane Database Syst Rev, 2011fckLRLevel of evidence: 1
- Liu H. and Frank A., Tai chi as a balance improvement exercise for older adults: a systematic review, J Geriatr Phys Ther, 2010fckLRLevel of evidence: 1
- Zheng J. et al., Strategic targeted exercise for preventing falls in elderly people, Journal of International Medical Research, 2013 Level of evidence: 2