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Since 2010, an increasing interest in more portable and flexible hardware for balance and posture assessment led to previously published studies determining whether or not the Wii Balance Board could be used to assess balance and posture, both scientifically and clinically. However, no previous studies aimed at comparing results from different Wii Balance Boards for clinical balance evaluation exist.
The objective of this crossover study is to assess the interchangeability of the Wii Balance Board.
A total of 6 subjects participated in the study and their balance was assessed using 4 different Wii Balance Boards. Trials were recorded simultaneously with Wii Balance Boards and with a laboratory force plate. Nine relevant clinical parameters were derived from center of pressure displacement data obtained from Wii Balance Board and force plate systems. Intraclass correlation coefficients (ICC),
Excellent correlations were found between the Wii Balance Board and force plate (mean ρ =.83). With the exception of 2 parameters, strong to excellent agreements were found for the 7 remaining parameters (ICC=.96). No significant differences were found between trials recorded with different Wii Balance Boards.
Our results indicate that for most of the parameters analyzed, balance and posture assessed with one Wii Balance Board were statistically similar to results obtained from another. Furthermore, the good correlation between the Wii Balance Board and force plate results shows that Wii Balance Boards can be reliably used for scientific assessment using most of the parameters analyzed in this study. These results also suggest that the Wii Balance Board could be used in multicenter studies and therefore, would allow for the creation of larger populations for clinical studies.
Ethical Committee of the Erasme Hospital (CCB B406201215142).
The potential use of the Nintendo Wii Balance Board for assessing balance and posture has already been previously investigated [
Most previously published papers on this particular topic reported a high correlation between a force plate and a Wii Balance Board for evaluating center of pressure trajectories. Such conclusions have therefore encouraged the use of Wii Balance Board hardware in daily clinical practice to assess balance in various pathological conditions such as Parkinson disease, orthopedics, and elderly assessment (eg, [
The present study presents the repeatability of balance measurements using 4 different Wii Balance Boards systems.
Healthy adults (N=6) with a mean age of 36 years (SD 13), height of 176 cm (SD 11), and weight of 81 kg (SD 22), including 2 women participated in the study. This study was approved by the Ethical Committee of the Erasme Hospital (CCB B406201215142) and all participants provided informed consent.
In order to assess the repeatability of Wii Balance Boards, the protocol of Huurnik et al was used [
The participants performed 3 repetitions of double limb standing on each available Wii Balance Board in a single session; the 4 Wii Balance Boards were tested in this one session (12 trials per subject). Subjects were asked to stand in the middle of the Wii Balance Board for 30 seconds, as motionless as possible, eyes open, arms aligned along the body, and eyes fixed on a target on the wall in front of them. The same methodology was repeated for the 4 different Wii Balance Boards. The order of the tested Wii Balance Board system was randomly determined.
Linear interpolation of the raw signals of the Wii Balance Board sensors was applied to get a regular sample rate of 1000 Hz (same as the force plate) [
Since the data recorded during posture measurement was highly variable between trials (eg, various foot positions on the force plate and concentration of the subject) the mean difference between force plate and Wii Balance Board values was computed for each studied parameter, for each 30 second trial in order to tackle this variability. All statistics were performed on the mean of the 3 trials for each Wii Balance Board (6 subjects and 4 Wii Balance Boards each).
Equations.
Parameter
DOT: total displacement of sway
Area: the area of the 95% prediction ellipse (often referred to as the 95% confidence ellipse)
SD AP and ML: the dispersion of center of pressure displacement from the mean position
AdCP_{AP} and AdCP_{ML}: the distance between the maximum and minimum center of pressure displacement
MV_{AP} and MV_{ML}: the mean velocity of center of pressure displacement
TMV: the AP and ML displacements of the total center of pressure sway divided by the total duration of the trial
Intraclass correlation coefficients (ICC) (twoway random average measures; Model 2, single measurement) were computed to assess the reliability of the differences between devices and trials. Friedman tests (repeated measures) were also computed to compare the 4 different Wii Balance Boards. Differences between the force plate and Wii Balance Board for each trial (3 repetitions for each of the 4 Wii Balance Boards for each subject (N=6) totals 72 trials) with mean difference and confidence intervals plotted. The amount of observations that were outside the confidence intervals for each variable and each Wii Balance Board were summarized in a contingency table. Chisquare tests were computed to detect interactions between the Wii Balance Board and studied variables. Spearman correlation coefficients were computed between variables obtained from the force place and Wii Balance Board.
ICC results for agreement between Wii Balance Boards and results of the
Intraclass correlation coefficient (ICC) of the studied parameters for the 4 different devices.
Variable  ICC agreement  Bounds of the confidence interval  Friedman, 



Lower  Upper 

DOT  .704  0.110  0.955  .93 
Area  .959  0.858  0.994  .91 
RMS_{AP}  .906  0.686  0.985  .42 
RMS_{ML}  .334  1.761  0.901  .87 
AdCP_{AP}  .786  0.336  0.965  .25 
AdCP_{ML}  .345  1.911  0.904  .72 
MV_{AP}  .985  0.950  0.998  .95 
MV_{ML}  .980  0.931  0.997  .86 
TMV  .984  0.945  0.997  .94 
The differences between each trial and the mean difference with confidence intervals are presented in
The correlations between the data collected with the force plate and Wii Balance Boards are shown in
Contingency table of the number of observations outside of the confidence interval.
Variable  Wii Balance Board device number 


1, n^{a}  2, n^{a}  3, n^{a}  4, n^{a}  Total, per variable  
DOT  1 (0.05)  1 (0.05)  3 (0.16)  0 (0)  5 (0.07) 
Area  2 (0.11)  1 (0.05)  2 (0.11)  0 (0)  5 (0.07) 
RMS_{AP}  2 (0.11)  0 (0)  1 (0.05)  2 (0.11)  5 (0.07) 
RMS_{ML}  1 (0.05)  0 (0)  2 (0.11)  1 (0.05)  4 (0.06) 
AdCP_{AP}  2 (0.11)  3 (0.16)  0 (0)  1 (0.05)  6 (0.08) 
AdCP_{ML}  1 (0.05)  0 (0)  2 (0.11)  1 (0.05)  4 (0.06) 
MV_{AP}  0 (0)  1 (0.05)  0 (0)  2 (0.11)  3 (0.04) 
MV_{ML}  3 (0.16)  1 (0.05)  1 (0.05)  1 (0.05)  6 (0.08) 
TMV  3 (0.16)  1 (0.05)  1 (0.05)  1 (0.05)  6 (0.08) 
Total, per device  15 (0.09)  8 (0.05)  12 (0.07)  9 (0.05)  44 
^{a}Values inside brackets represent the ratio between outside values and number of observations.
Differences between force plate and Wii Balance Boards for the 72 trials. Solid horizontal lines represent the mean difference. Dotted horizontal lines represent upper and lower confidence intervals (95%). Vertical lines indicate separation between the 4 different devices (18 trials per Wii Balance Board).
Spearman correlation coefficients between the force plate and the 4 different Wii Balance Board devices.
Variables  Wii Balance Board device number 


1, ρ  2, ρ  3, ρ  4, ρ  Mean, ρ  
DOT  .79  .73  .73  .87  .78 
Area  .85  .89  .82  .90  .86 
RMS_{AP}  .79  .92  .85  .78  .83 
RMS_{ML}  .85  .72  .72  .80  .76 
AdCP_{AP}  .76  .89  .74  .79  .80 
AdCP_{ML}  .89  .79  .76  .73  .79 
MV_{AP}  .94  .89  .88  .90  .91 
MV_{ML}  .96  .84  .85  .91  .89 
TMV  .82  .80  .77  .86  .81 
Mean, ρ (SD)  .85 (0.02)  .83 (0.02)  .79 (0.02)  .84 (0.02)  .83 (0.05) 
To the best of our knowledge, this is the only study assessing the repeatability of measurements performed with different Wii Balance Boards. Our results confirm the findings of previous studies [
With respect to the 4 different Wii Balance Boards, no differences were found between the boards (repeated measure Friedman test), but surprisingly, the ICC values showed low agreement for the ML parameters (RMS_{ML} and AdCP_{ML}) although correlations with the force plate were high (.80 and.89 for RMS_{ML} and AdCP_{ML}, respectively). The contingency table of the number of observations outside of the confidence intervals did not show particular errors for those measurements (
This study presents results on several different parameters derived from center of pressure displacement. Most other studies have focused on investigating differences between Wii Balance Boards and a force plate for a single parameter (eg, center of pressure displacement) [
The repeatability of some balance assessment protocols can be rather low. In our setup, we ran the risk of suffering from the same problem: in order to compare all the Wii Balance Boards and the force plate in a single trial, we would have had to place all the boards together on top of the force plate. As this is unfeasible, we processed our data by computing the difference between the Wii Balance Board and the force plate (for all the parameters) for each of the 4 trials. Over 3 trials and 6 subjects, we obtained 4 groups of 18 differences. ICCs were computed between those 4 groups. As the ICCs were high, the differences between the Wii Balance Board and force plate were considered consistent.
This study indicates that balance and posture results recorded with one Wii Balance Board can be compared to the results recorded with another Wii Balance Board. This is particularly interesting for multicenter studies and supports the creation of larger populations for clinical studies. This study also allows us, in part, to address several criticisms that have recently been expressed. Some researchers [
anteriorposterior
Total displacement of sway
Intraclass correlation coefficient
mediolateral
Mean velocity
Total mean velocity
This study is a part of the ICT4Rehab and RehabGoesHome projects. These projects are funded by Innoviris (Brussels Capital Region).
None declared.