Dušan Hamar

Helmut Kern

Ján Cvečka

Milan Sedliak

Nejc Šarabon

Stefan Löfler

Veronika Tirpáková

European Journal of Translational Myology

English

Crossref

Novel postural sway task test 
European Journal Translational Myology - Basic Applied Myology 2013; 23 (3): 81-84 
- 81 - 
 
Reliability of novel postural sway task test 
Milan Sedliak (1), Ján Cvečka (1), Veronika Tirpáková (1), Stefan Löfler (2,3), Nejc 
Šarabon (4), Helmut Kern (2,3), Dušan Hamar (1) 
(1) Faculty of Physical Education and Sports, Comenius University, Bratislava, 
Slovakia; (2) Department of Physical Medicine and Rehabilitation, Wilhelminenspital, 
Vienna, Austria; (3) Ludwig Boltzmann Institute of Electrical Stimulation and 
Physical Rehabilitation, Vienna, Austria; (4) University of Primorska, Science and 
Research Centre, IKARUS, Koper, Slovenia 
Abstract 
The purpose of this study was to examine the reliability of parameters obtained from a novel 
postural sway task test based on body movements controlled by visual feedback. Fifty-nine 
volunteers were divided into two groups. The first group consisted of young (n = 32, 16 
females and 16 males, age: 25.2 ± 3.4 years) and the second group of elderly individuals (n = 
27, 17 females and 10 males, age: 75.7 ± 6.9 years). Participants stood in parallel on a 
computer based stabilographic platform with the feet approximately a shoulder width apart, the 
toes slightly pointing outwards, the hands placed on the hips. The computer screen was placed 
approximately 1.5 meter from the platform at a height of subjects’ eyes. An instantaneous 
visual feedback of participant’s centre of pressure (COP) was given in a form of a blue cross 
visible on the screen. Participants were instructed to keep the blue cross driven by movements 
of their hips as close as possible to a predefined curve flowing on the screen. Out of the 6 
parameters studied, only the average distance of COP from the curve line and the sum of the 
COP crossings through the curve line showed high reliability. Correlation between these two 
highly reliable parameters was -0.89. There was also a statistical difference (p<0.001) between 
young and elderly in both the average distance of COP from the curve line and the sum of the 
COP crossings through the curve. To conclude, the novel postural sway task provides a simple 
tool with relatively low time burden needed for testing. The suggested output parameters 
measured are highly reliable and easy to interpret. 
Key Words: balance, centre of pressure, postural control, task test, visual feedback 
European Journal Translational Myology - Basic Applied Myology 2013; 23 (3): 81-84
 Maintaining an upright posture is an essential part of 
still standing as well as basic human locomotion types 
e.g., walking and running. Hence, the evaluation of 
postural control has been widely used in research and 
clinical settings in various populations, ranging from 
elderly patients to athletes [11,7]. One of the most 
widely used methods is recording the movement of the 
centre of pressure (COP) during still standing, so called 
static balance. The COP is the point of application of 
the resultant ground reaction force vectors. Typically, a 
subject is standing on a force platform, which allows 
recording the COP sway exerted to maintain the centre 
of mass (COM) as still as possible. These types of 
tests, which analyse the sway of COP, have been 
repeatedly reported to have a good reliability level (for 
a review see e.g., [13]). A recent report of Robinovitch 
et al. [12] showed that the most common reason of falls 
among the elderly is incorrect COM transfer during 
movement e.g., during standing up or stepping 
sideway. There are also several laboratory and field 
tests which examine stability while a subject 
voluntarily or involuntarily moves the whole or parts 
of their body and hence induces COM transfer. They 
range from tests with minimal requirement for 
instrumentation to computerized dynamic 
posturography. For instance, the Star Excursion 
Balance Test [5] and Functional Reach Test [4] use 
simple measurements of reaching distance and do not 
require any electric or electronic devices. Such a 
simplistic approach has undoubtedly many advantages, 
but it may, in part, compromise the value of the 
information obtained. On the other hand, there are 
complex systems like Equi Test (NeuroCom 
International, Clackamas, USA) selectively 
Novel postural sway task test 
European Journal Translational Myology - Basic Applied Myology 2013; 23 (3): 81-84 
- 82 - 
 
 
 
Table 1. Intraclass correlation coefficients (ICC R) in the studied parameters 
______________________________________________________________________________________  
Parameters AverDist  COPCrossing  AverDist R  AverDist L  AverRoute R  AverRoute L 
 
ICC R  0.968  0.934  0.856  0.798  0.861  0.763   
Pearson r  0.89 
______________________________________________________________________________________ 
Pearson’s correlation coefficient (Pearson r) was calculated only for the parameters with ICC R higher than 0.90. 
 
 
 
Fig 1. A screen shot of the test graphics seen by a 
subject. A – position of the subject’s COP, B - curve 
line followed, C - average distance of the COP from 
the curve line at the certain recording point. 
manipulating the visual field and ground surface to 
enable discrimination of the contribution of visual, 
vestibular, and somatosensory systems to maintaining 
balance. It is clear that such systems provide more 
complex information, however, with considerably 
higher financial costs and time demands. In our 
opinion, the tests using monitoring of height 1.65 ± COP 
during simple tasks performed on a force platform may 
provide a good compromise between the costs and the 
information obtained. One example of such test is the 
Functional Reach Test performed on the force 
platform. However, there exists scientific consensus 
that the control of gait and balance entails attentional 
capacity [1,17,18] which is not included within e.g., 
the Functional Reach Test. It would be therefore more 
relevant, in our opinion, to combine monitoring COP 
during voluntary body movement with an attentional 
task. Only a few studies using the above mentioned 
approach e.g., [3,9] have been published so far. In 
addition, their findings were not always conclusive and 
the methodology varied significantly. Therefore, this 
study presents a novel postural sway task test based on 
voluntary body movements controlled by visual 
feedback. The purpose of the present study was to 
examine the reliability of parameters obtained from 
such a novel task test. 
Materials and Methods 
Subjects 
 Fifty-nine volunteers were divided into two groups. 
The first group consisted of young individuals (n = 32, 
16 females and 16 males, age: 25.2 ± 3.4 years; weight 
66.3 ± 10.0 kg, height 1.74 ± 0.075 m), whereas the 
second one of elderly individuals (n = 27, 17 females 
and 10 males, age: 75.7 ± 6.9 years; weight 72,4 ± 12.6 
kg, height 1.65 ± 0.079 m). None of the participants 
reported musculoskeletal or neurological disorders that 
would limit their ability to take part in the study. The 
study was approved by the Ethics Committee of 
Faculty of Physical Education and Sports, Comenius 
University, Bratislava, Slovakia and was in compliance 
with the Helsinki Declaration .An informed consent 
form was read and signed by each of the subjects prior 
to the investigation. 
Experimental protocol 
Participants stood on a computer based stabilographic 
platform (Fitro SwayCheck, Fitronic, Bratislava, 
Slovakia) in a parallel stance, feet approximately a 
shoulder width apart, toes slightly pointing outwards, 
hands placed on the hips. A computer screen was 
placed approximately 1.5 meter from the platform at 
height of subject’s eyes. An instantaneous visual 
feedback of participant’s COP was given in a form of a 
blue cross visible on the screen. Participants were 
instructed to keep as close as possible with the blue 
cross driven by movements of his/her hips to a 
predefined flowing curve (Figure 1). The length and 
thickness of the two cross lines were 16 and 5 pixels, 
respectively. The curve was moving from the top of the 
screen downwards and the subject copied its shape by 
their body movements (COP displacement) in 
mediolateral direction (ML). The curve parameters 
were programmed with a custom-made software and 
were identical in all tests. Curve was flowing in a 
downward vertical direction with the velocity of 0.03 
ms-1 Waveform fluctuations around the vertical line 
were randomly generated by the control software. The 
extent of the amplitude was always less than subjects’ 
ability to transfer their COP in the directions required. 
The system monitored horizontal distance between 
Novel postural sway task test 
European Journal Translational Myology - Basic Applied Myology 2013; 23 (3): 81-84 
- 83 - 
 
Table 2. Parameters of COP during the task test with ICC R higher than 0.90 in groups of young and elderly subjects 
__________________________________________________________________________________________ 
 
   AverDist Test AverDistRetest COPCrossing Test COPCrossing Retest 
 
Young  12.08 ± 2.52 10,54 ± 2.53 52.35 ± 9.65 54.56 ± 12.72 
 
Elderly        25.76 ± 8.27***       20.87 ± 6.17***      26.83 ± 10.29*** 28.38 ± 11.26*** 
__________________________________________________________________________________________ 
 
(means ± SD). *** - statistically significant at p<0.001. 
projection of COP on the screen and flowing curve as 
well as its velocity at the rate of 100 Hz. A sum of 
horizontal crossings of the COP trace across the 
flowing curve was recorded, as well. Duration of each 
test trial was 30 seconds. Prior to the actual testing, 
each subject carried out one familiarization trial. 
Subsequently, three trials of ML (Test) were performed 
with a 60-second rest period. Subjects were free to 
either stand relaxed or make several slow steps 
between the trials. After approximately a 20-minute 
rest period, the same set of 3 trials was carried out 
again (Re-test).  
Data and statistical analyses 
The following parameters were calculated from the 
data acquired: 
(AverDist), average distance of the COP from the 
curve line  
(AverDist L) average distance of the COP from the 
curve line on the left side of the curve  
(AverDist R) average distance of the COP from the 
curve line on the right side of the curve  
(AverRoute L) average curve route of the COP left 
from the curve line  
(AverRoute R) average curve route of the COP right 
from the curve line  
(COPCrossing) sum of the COP crossings through the 
curve line . 
When all data were merged, intraclass correlation 
(ICC) was applied to calculate the reliability 
coefficient (R) with the IBM SPSS software (IBM, 
NY, USA). The reliability coefficients were evaluated 
according to Vincent [15] as follows: R>0.90 – high 
reliability, R=0.80 – 0.90, moderate reliability, R<0.80 
– questionable.  
Subsequently, Pearson’s correlation coefficients 
between variables with ICC R higher than 0.90 to 
assess their relationship were calculated.  
In addition, independent-samples t-test was used to 
evaluate the differences between the groups of young 
and elderly subjects separately for Test (mean of 3 
trials) and Retest (mean of 3 trials). The independent-
samples t-test was selected to estimate the sensitivity 
of the test for discrimination between two 
heterogeneous groups of the young and elderly. 
Results and Discussion 
Out of the 6 examined parameters, only AverDist and 
COPCrossing showed high reliability. Correlation 
between AverDist and COPCrossing was -0.89 (Table 
1). Both parameters with ICC R higher than 0.90 were 
significantly different in the group of young subjects 
compared to the group of elderly subjects (Table 2). 
Typically, variety of COP shift indices during still 
stance or voluntary COP movements are used, e.g. 
mean velocity, frequency, area, amplitude, sway index, 
COP sway area. [6,10,14]. In extreme case, thirty four 
parameters have been evaluated within a single study 
[8]. In a literature review focused on bipedal static task 
conditions, Ruhe et al. [13] concluded that the 
reliability of traditional COP parameters is acceptable 
if specific recommendations are followed in the study 
design. While having several parameters providing 
complex information about the COP shifts may be of 
advantage in research settings, in clinical practice, a 
single parameter to interpret would be ideal for both 
the clinician and the patient. In the present study, we 
found that out of six parameters studied, the average 
distance of COP from the curve line showed the 
highest reliability. Based on Vincent [15], reliability 
coefficients can be considered as having high 
reliability if R is bigger than 0.90.  
Besides the average distance of COP from the curve 
line, also the parameter giving the sum of COP 
crossings through the curve line provided high 
reliability. Apart from that, both parameters were 
similarly and significantly sensitive to distinguish 
between young and elderly subjects (Table 2). In both 
cases, young subjects achieved approximately 50% 
better performance compared to elderly subjects. Both 
variables were also highly correlated suggesting that 
they measure the same physiological mechanism(s) 
controlling COP voluntary shifts. Therefore, the 
average distance of COP from the curve and the sum of 
COP crossings through the curve line could be used as 
an output parameter in the novel postural sway task test 
with visual feedback. In our opinion, the latter 
parameter provides smoother continuum values 
compared to the former one, which may be of an 
advantage. It should be noted that the present postural 
sway task test with visual feedback could be performed 
both in anterior-posterior and mediolateral direction. 
Novel postural sway task test 
European Journal Translational Myology - Basic Applied Myology 2013; 23 (3): 81-84 
- 84 - 
 
However, in the present study, we used only 
mediolateral direction since previous research has 
shown that indices of sway in the mediolateral 
direction increased more significantly than those of 
sway in the anterior-posterior direction during 
voluntary COP shifts. Latash et al [9] suggested that 
large COP shifts in the anterior-posterior direction are 
common in everyday activities such as making a step 
or standing up from the chair. On the contrary, COP 
shifts in the mediolateral direction are less common 
and are typically of a smaller magnitude [2,16]. 
Therefore, larger movements in the anterior-posterior 
direction may be considered a consequence of a more 
active search in the direction the person is more likely 
to move, for example to make a step. However, during 
a voluntary COP shift, the search function of the sway 
may be suppressed leading to a proportionally smaller 
increase in the sway in the AP direction, or even to its 
decrease, opposite to the mediolateral direction [9]. In 
addition, incorrect COM transfer during voluntary 
sideway (mediolateral) movements were shown to be 
the leading cause for falls in the elderly [12]. Studying 
indices of sway in the mediolateral direction during 
voluntary COP shifts is, in our opinion, of a high 
practical importance.  
In conclusion, the novel postural sway task provides a 
simple tool with relatively low time burden needed for 
testing. The suggested output parameters measured are 
highly reliable and easy to interpret. 
Acknowledgements 
This study was supported by the European regional 
development fund (ERDF, Interreg IVa Project 
N_00033 MOBIL). 
Corresponding Author 
Milan Sedliak, PhD., Nabr. arm. gen. L. Svobodu 9, 
814 69 Bratislava, Slovakia 
e-mail:  msedliak@yahoo.com  
References 
[1] Alexander NB, Hausdorff JM. Linking thinking, 
walking, and falling. J Gerontol A Biol Sci Med 
Sci 2008; 63A: M1325–M1328. 
[2] Duarte M, Zatsiorsky VM. On the fractal 
properties of natural human standing. Neurosci 
Lett 2000; 283: 173–176. 
[3] Duarte M, Freitas SM. Speed-accuracy trade-off 
in voluntary postural movements. Motor Control 
2005; 9: 180-196.  
[4] Duncan, P.W., Weiner, D.K., Chandler, J. & 
Studenski, S.  Functional reach: a new clinical 
measure of balance. J Gerontol 1990; 45: M192-
M197. 
 [5] Gray G W. Lower Extremity Functional Profile. 
Adrian, MI: Wynn Marketing Inc., 1995, pp 161. 
 [6] Hageman PA, Leibowitz JM, Blanke D. Age and 
gender effects on postural control measures. Arch 
Phys Med Rehabil 1995; 76: 961–965. 
 [7] Hrysomallis C, McLaughlin P, Goodman C. 
Relationship between static and dynamic balance 
tests among elite Australian Footballers. J Sci 
Med Sport 2006; 9: 288-291.  
 [8] Kitabayashi T, Demura S, Noda M. Examination 
of the factor structur eof center of foot pressure 
movement and cross-validity. J Physiol Anthropol 
Appl Human Sci 2003; 22: 265–272. 
 [9] Latash ML, Ferreira SS, Wieczorek SA, Duarte 
M. Movement sway: changes in postural sway 
during voluntary shifts of the center of pressure. 
Exp Brain Res 2003; 3: 314-324. 
[10] Mattacola CG, Lebsack DA, Perrin DH. Inter 
tester reliability of assessing postural sway using 
the chattecx balance system. J Athl Train 1995; 
30: 237–242. 
 [11] Menegoni F, Galli M, Tacchini E, Vismara L, 
Cavigioli M, Capodaglio P. Gender-specific 
effect of obesity on balance. Obesity 2009; 17: 
1951-1956.  
 [12] Robinovitch SN, Feldman F, Yang Y, Schonnop 
R, Leung PM, Sarraf T, Sims-Gould J, Loughin 
M. Video capture of the circumstances of falls in 
elderly people residing in long-term care: an 
observational study. Lancet 2013; 381: 47-54. 
 [13] Ruhe A, Fejer R, Walker B The test-retest 
reliability of centre of pressure measures in 
bipedal static task conditions--a systematic 
review of the literature. Gait Posture 2010 ; 32: 
436-445.  
 [14] Takala EP, Korhonen I, Viikari-Juntura E. 
Postural sway and stepping response among 
working population: reproducibility, long-term 
stability, and associations with symptoms of the 
low back. Clin Biomech 1997;12: 429–437. 
 [15] Vincent WJ. Statistics In Kinesiology, Human 
Kinetics, 2005, pp 311. 
 [16] Winter DA, Patla AE, Prince F, Ishac M, Gielo-
Perczak K Stiffness control of balance in quiet 
standing. J Neurophysiol 1998; 80: 1211–1221. 
 [17] Woollacott M, Shumway-Cook A. Attention and 
the control of posture and gait: a review of an 
emerging area of research. Gait Posture 2002; 
16:1–14. 
 [18] Yogev-Seligmann G, Hausdorff JM, Giladi N. 
The role of executive function and attention in 
gait. Mov Disord 2008; 23: 329–342. 
 


Reliability of novel postural sway task test

https://www.pagepressjournals.org/index.php/bam/article/download/bam.2013.3.81/1273

Reliability of novel postural sway task test

Abstract

Similar works

Full text

Available Versions

Crossref

Crossref