The goal of the SwayStar™ measurements is to make direct comparisons between the amplitudes of trunk instabilities in different groups of subjects for both stance and gait tasks. Including task duration as a measurement makes it possible to weight the information content of duration relative to trunk-sway variables. Clinicians will want to compare a test subject’s values to normal reference values and then decide, based on the pattern of the deviations from the reference values, whether the subjects’ values are likely to be similar to those of a specific patient group. Examples of this procedure for different patient groups are provided in the following list of clinical-scientific literature. The reviews provide up-to-date summaries.




Allum JHJ, Carpenter MG, Adkin AL. Balance Control Analysis as a method for screening and identifying balance deficits. In: The vestibular Labyrinth in Health and Disease. Eds J Goebel and S.M. Highstein Annal NY Acad Sciences 2001, Vol. 942:413-427.


Allum JHJ, Carpenter MG. A speedy solution for balance and gait analysis: angular velocity measured at the centre of mass. Current Opinions in Neurology 2005, 18: 15-21.


Allum JHJ, Carpenter MG. Erkennung und Rehabilitation von Sturztendenzen und Gleichgewichts-Funktionsstörungen mittels Posturographie. Vestibularfunktion (ed M Westhofen) Springer Verlag, Vienna 2006, pp 141-156.


Allum JHJ Gleichgewichtskontrolle – Klinische Bedeutung und praktische Relevanz. HNO Praxis heute Band 27: Schwindel Eds E Biesinger and H Iro, Springer Verlag, Heidelberg 2007, p 47-58.



Clinical Scientific (Sway Star™):


Adkin AL, Allum JHJ, Bloem BR. Trunk sway measurements during stance and gait tasks in Parkinson’s disease. Gait and Posture 2005, 22: 240-249


Allum JHJ, Held-Ziolkowska M, Adkin AL, Carpenter MG, Honegger F. Trunk sway measures of postural stability during clinical balance tests: effects of a unilateral vestibular deficit. Gait and Posture 2001, 14:227-237


Allum JHJ, Zamani F, Adkin AL, Ernst a. Differences between trunk sway characteristics on a foam support surface and on the Equitestâ ankle-sway-referenced support surface. Gait and Posture 2002, 16:264-270


Allum JHJ, Adkin AL. Improvements in Trunk sway for stance and gait tasks during recovery from an acute unilateral peripheral vestibular deficit. Audiology and Neurootology 2003, 8: 286-302


Basta D, Todt I, Scherer H, Clarke A, Ernst A. Postural control in otolith disorders. Hum Mov Sci, 2005, 24:268-279


Basta D, Clarke A, Ernst A, Todt I. Stance performance under different sensorimotor conditions in patients with post-traumatic otolith disorders. J Vest Res, 2007, 17:25-31


Beule AG, Allum JHJ. Otolith function assessed with the subjective postural horizontal and standardised stance and gait tests. Audiol Neurootol 2006, 11: 172-182


Bischoff-Ferrari HA, Conzelmann M, Stähelin HB, Dick W, Carpenter MG, Theiler R, Allum JHJ. Is fall prevention with vitamin D mediated by a change in postural or dynamic balance? Osteoporos Int 2006, 17: 656-663


De Hoon EWJ, Carpenter MG, Salis C, Allum JHJ, Bloem BR, Conzelmann M, and Bischoff H. Quantitative Assessment of the “stops walking while talking test” in the elderly. Arch Phys Med and Rehab 2003, 89: 838-842


Ernst A, Basta D, Seidl RO Todt I, Scherer H, Clarke A. Management of posttraumatic vertigo. Otolaryngol Head Neck Surg. 2005, 132:554-558 


Gill J, Allum JHJ, Carpenter MG, Held-Ziolkowska M, Honegger F, Pierchala K. Trunk sway measures of postural stability during clinical balance tests: effects of age. J Gerontology 2001, 56A:M438-M447


Grimbergen YA, Knol MJ, Bloem BR, Kremer BP, Roos RA, Munneke M. Falls and gait disturbances in Huntington’s disease. Mov Disord 2008, 23;970-976



Hegeman J, Shapkova E, Honegger F, Allum JHJ. Effect of age and height on trunk sway during stance and gait. J Vest Res 2007,17:75-87.


Horlings GC, Drost G, Bloem BR, Trip J, Pieterse AJ, Van Engelen BGM, Allum JHJ. Trunk sway analysis to quantify the warm-up phenomenon in myotonia congenita patients. J Neurol Neurosurg Psychiatry. 2008 (in press). 


Horlings GC, Kueng UM, Honegger F, Bloem BR, Van Alfen N, Van Engelen BGM, Allum JHJ. Identifying vestibular and proprioceptive loss using posturographic analysis of stance tasks. Clinical Neurophysiology 2008, 119:2338-2346.


Horlings CGC, Carpenter MG, Kueng UM, Honegger F, Yun M, Wiederhold B, Allum JHJ

Influence of virtual reality on postural stability during quiet stance. Neuroscience Lett 2009, (in press)


Majewski M, Bischoff-Ferrari HA, Grueneberg C, Dick W, Allum JHJ. Improvements in balance after total hip replacement. J Bone Joint Surg Br. 2005, 10: 1337-1343


Schmuziger N, Allum J, Buitrago- Tellez C, Probst R. Incapacitating hypersensitivity to one's own body sounds due to a dehiscence of bone overlying the superior semicircular canal. A case report. Eur Archiv Otorhinolaryngol 2006, 263: 69-74


Sjöström H, Allum JHJ, Carpenter MG, Adkin AL, Honegger F, Ettlin T. Trunk sway measures of postural stability during clinical balance tests in patients with chronic whiplash symptoms. Spine 2003, 28: 1725-1734 


Van de Warrenburg BPC, Bakker M, Kremer HPH, Bloem BR, Allum JHJ. Trunk sway in patients with cerebellar ataxia. Movement Disorders 2005, 20: 1006-1013 


Visser JE, Voermans NC, Oude Nijhius LB, van der Eijk M, Nijk R, Munneke M, Bloem BR. Quantification of trunk rotations during turning and walking in Parkinsons’s disease. (in press)


Vrancken AMPM, Allum JHJ, Siebner HR, Peller M, Visser J, Bloem BR. Effect of bilateral  subthalamic nucleus stimulation on balance and finger control in Parkinson’s disease. J Neurology 2005, 252:1487-1494



Clinical Scientific (Balance Freedom™)


Allum JHJ, Davis JR, Carpenter MG, Tschanz R, Meyes S, Debrunner D, Burger J. Neue Ansätze zur Sturzprävention mittels einer multi-modalen Gleichgewichtsprothese. In Neues aus Forschung und Klinik 6. Hennig Symposium: Der Gleichgewichtssinn. (ed H Scherer) Springer Verlag 2008 p 211-221


Allum JHJ, Davis JR, Carpenter MG, Tschanz R, Meyes S, Debrunner D, Burger J. Neurofeedback in der Rehabilitation von Gleichgewichtsstörungen. at-automatiserungstechnik 2008, 56:467-475.


Basta D, Singbartl F Todt I, Clarke A, Ernst A. Postural control in otolith disorders. Vestibular rehabilitation by auditory feedback in otolith disorders. Gait and Posture, 2008, 28:397-404


Davis JR, Carpenter MG, Tschanz R, Meyes S, Debrunner D, Burger J, Allum JHJ. Trunk sway reduction in the young and elderly using vibrotactile and auditory biofeedback. Submitted to J Gerontology


Hegeman J, Honegger F, Kupper M, Allum JHJ. The balance control of bilateral peripheral vestibular loss subjects and its improvement with auditory prosthetic feedback. J. Vest Res 2005, 15:109-117.


Horlings CGC, Honegger F, Allum JHJ, Carpenter MG. Vestibular and proprioceptive contributions to human balance corrections: aiding those with prosthetic feedback. Proc NYAS 2009(in press)


Janssen LJF, Verhoeff LL, Horlings CGC, Allum JH. Directional effects of biofeedback on trunk sway during gait tasks in healthy young subjects. Gait and Posture 2009 (in press)


Verhoeff LL, Janssen LJF, Horlings CGC, Allum JHJ. Effects of biofeedback on trunk sway during dual tasking in healthy young and elderly. Gait and Posture 2009(in revision)



2.2.1  Advantages of SwayStar™ compared to other types of equipment 

SwayStar™ directly measures the angular deviations of the trunk near the centre of mass (around L3-L5) without relying on indirect calculations obtained from measuring forces imposed on strain gauges embedded within a support surface or body marker information supplied by motion analysis systems. The measurement system of SwayStar™ is mounted on a belt. This mode of measurement makes the system portable, quick and easy to use.


Measuring trunk angular motion near the centre of gravity is probably the most effective way to quantify a falling tendency. It is independent of the linear motion of the body, that is, how fast one is walking. Measuring at another body segment might not quantify a balance instability. For example, motion of the head alone would not, because head movements are often independent from those of the trunk.


With the Bluetooth communication system SwayStar™ employs, the test subject can be up to 100 m away from the base measuring system at the PC. Other systems using camera, ultra-sonic or magnetic based sensor systems lack this huge field of operation.


Current camera-based, linear-displacement, motion analysis systems have limitations for analyzing body sway. They lack the sensitivity to accurately monitor small angular movements, they operate within frequency bandwidths that are too low (less than 50 Hz) to quantify a range of angular velocities accurately and the subject is often confined to a pre-defined test area making it difficult to perform and record gait tasks. Such motion analysis systems require repeated calibration to ensure that angles calculated from marker movements on the body are accurate. SwayStar™ avoids the limited accuracy, narrow bandwidth of such systems, and intensive operator costs. The SwayStar™ system measures as accurately as the earth’s rotation (0.01 deg/sec) how the trunk is moving during different real-time tasks without significantly limiting the subject’s movements. One of the prime disadvantages of motion analysis system is the need for dedicated technical personnel to operate the system and to produce the angular measurements that SwayStar™ produces automatically.


Thus one of the main advantages of SwayStar™ is that it can be used to measure the small movements of body sway during stance tasks, and it can be used to measure large sway movements of gait tasks, for example the getting up off a stool phase as part of the get-up-and-go task.


Stance tests can be performed in many forms with SwayStar™. One of the most common is on two legs, with and without vision, and like with computerised dynamic posturography (CDP) with an unstable surface. A foam pad is used as the unstable surface with SwayStar™. By comparing the values of sway under different visual and support surface conditions it is possible to assess the visual, somatosensory and vestibular contributions to stance control just as with CDP, however, not just in the pitch direction. The assessment can be made for the roll direction too which standard CDP equipment cannot perform.



2.2.2  Advantages of Balance Freedom™ 

A new addition to SwayStar™ is the combined vibro-tactile and auditory feedback system – Balance Freedom™. Signal transducers mounted on a head-band are driven by the sensors of SwayStar™. Thereby acoustic and vibratory feedback is provided to the patient on the status of his balance control, that is, the leaning motion of his trunk. Thresholds for the activation of vibro-tactile and auditory feedback are set at low and medium angles of trunk sway. A visual warning signal is also activated when the patient leans more than a higher set threshold.


The use of vibro-tactile feedback at head reduces the transmission time of these signals to the CNS. Furthermore this system used bone-conducting acoustic transducers to provide auditory feedback thereby opening up the air conduction pathway for normal hearing instead of blocking it with loudspeakers or in-ear speakers. Finally combined bone-conducting acoustic transducers and vibro-tactile devices mounted on the head may also excite otolith pathways and provide a means of artificial feedback.


The Balance Freedom™ system replaces the Auditory Feedback System Model 1. This system used 4 loudspeakers to provide auditory feedback (see Hegeman et al 2005 in reference list section 2.2.) produced by BII and now obsolete. The Auditory Model 1 system is still software supported.