The modified clinical test of sensory integration and balance (mCTSIB) performed on the Wii balance board: A validity study

Abstract

Introduction

Although often classified as a motor skill, standing balance relies on three sensory systems: vestibular, proprioception, and visual. To assess balance by challenging these systems, the rater uses the Modified Clinical Test of Sensory Integration and Balance (mCTSIB). However, valid low-cost equipment is unavailable for continuous patient monitoring.

Objective

The aim of the present study was to assess the validity of the Wii balance board (WBB) compared to a standard force platform during the mCTSIB.

Methods

A sample of 50 participants (17 men and 33 women; 23.34 [3.10] y; 1.68 [0.08] m; 68.82 [13.55] kg) was included. The average total COP displacement was simultaneously collected during standing balance from both WBB and the force platform under four conditions: eyes opened and closed with and without a foam cushion.

Results

No significant differences were observed between the WBB and the force platform. The correlation was considered high (r > .98; p = .001), with excellent adjusted coefficients of determination (.97 < r² < .99). The Bland–Altman method revealed low bias, and the majority of the results were scattered between the lower and upper levels of agreement.

Conclusions

The present findings suggest the validity of the WBB to assess the balance during the mCTSIB.

Keywords

proprioception vision vestibular

Introduction

Although often classified as a motor skill, standing balance heavily relies on three sensory systems: vision, proprioception and vestibular.^1,2 The 1^st transmits balance information through skin, muscle, and joint receptors, mainly conveying changes in ankle joint position and body sway.^3,4 In contrast, the visual system provides information about head position relative to the surrounding environment, which can aid in anticipating potential balance loss.⁵ In comparison, the vestibular system provides an inertial gravitational reference system that helps to maintain the balance, serving as an internal conflict resolution system that processes information regarding head positional equilibrium without relying on external cues.^2,5,6 Each of the above-mentioned systems collaborate to maintain the standing balance, and their contribution is crucial during the upright posture without falling.^1–5 Thus, postural control has a complimentary and multifactorial nature, and the actual individual contribution of each system is essential to best target the optimal intervention.

In this sense, the Modified Clinical Test of Sensory Integration and Balance (mCTSIB) is used to assess the ability to maintain the body balance under distinct sensory conditions.^1,4,6 It is often used to evaluate individuals with neurological conditions, such as Parkinson’s disease, stroke, and multiple sclerosis, as well as those with vestibular disorders, which affect the inner ear and the balance system.^7–9 The mCTSIB can also be used to assess the effects of a medication or other interventions on balance control.^10–12 However, the best quality of the mCTSIB relies on its ability to separately assess the contribution of each sensory system for balance control.⁶ The test involves four different sensory conditions that challenge balance control. The individual is asked to maintain balance for 20–30 s, depending on the protocol, in each condition: (1) To stand on a firm surface—eyes open; (2) To stand on a firm surface—eyes closed; (3) To stand on an unstable foam surface—eyes open; and (4) To stand on a unstable foam surface—eyes closed.^4,6 During the conventional test, the professional observes any compensatory movements, such as swaying or stepping to maintain the balance. The results of the test would provide information about the sensory processing abilities and might help guide treatment plans for those with balance impairments. However, the single mCTSIB observational assessment is still limited by lacking objective measures that ensure reliability to track any balance improvement or decrement in a given timeline.⁶

Previous studies proposed the instrumented mCTSIB, which consists on performing the test on a force plate.^4,13 The procedure allows tracking the center of pressure (COP) path length, an essential biomarker often used to discriminate, summarize and characterize the postural balance status.^4,13 By partially isolating the proprioceptive, visual, and vestibular systems during the instrumented mCTSIB, it is possible to estimate their unique contribution to maintain the balance.^1,3,4,13,14 In fact, evidence already suggested normative values for mCTSIB comprising more than 1250 individuals using a commercial force platform to acquire COP data during the 4-phase test (20-s per phase).^6,15 The normative values’ analysis identified the COP percentiles according to the sample’s sex and age. The percentiles were then attributed to classification of normal ranges of COP path length for each sensory condition. The main problem of this type of analysis is the cost of the force platform. Aside to that, the majority of force platforms are not portable, and require also expensive software license to extract data.^16,17

An interesting option to force platforms is the Wii Balance Board (WBB).^18–21 It has been widely used to assess balance in several conditions.^22–26 The validity and the reproducibility of the WBB measurements were also tested several times for many health conditions across all ages, resulting in a very affordable and reliable system compared to laboratorial force platforms.^{18–20,23,24,27–29} The WBB offers several benefits to objectively extract COP data: (1) Online available and reliable freeware to collect and export the results; (2) Easy-to-set Bluetooth connection to pair with a computer; (3) Portability, as the WBB’s weight and size are minimal compared to other force platforms; and (4) Similar extractable parameters for offline analysis compared to a force platform (COP path length, sway velocity and amplitude, and frequency analysis).^19,30 Despite all the above-mentioned advantages, only few studies used the WBB to perform the mCTSIB, and the single validation study did not show all the requirements needed to establish the actual validity of the WBB to conduct the mCTSIB (no sample size calculation, limited statistical analysis, and poor sample description).³¹ The validation study was also restricted to a sample of high functional older adults that, even functional, may show wider ranges of COP displacement. The validity would be more accurately assessed in a more limited range of COP displacement, where minimal changes would affect significantly the balance outcome. In this sense, healthy young adults might be the choice for such analysis.

Several patients may take benefit of the mCTSIB with more accurate balance diagnosis using the WBB. Clinicians may also expand their balance analysis of different systems to establish the correct source of the disorder, not diagnosed by a simple test (such as dizziness, tinnitus, and visual impairments). In the light of that, the purpose of the current study was to analyze the validity of the WBB compared to a standard force platform to perform the mCTSIB. The hypothesis of the present study was that the mCTSIB administered with the WBB would demonstrate good validity when compared to a gold-standard platform, supporting its use as a low-cost and accessible tool for evaluating postural control.

Materials and methods

Participants

A convenience sample of 50 participants from both sexes (17 men and 33 women; 23.34 [3.10] y; 1.68 [0.08] m; 68.82 [13.55] kg) were recruited by personal contacts and public invitation using digital folders. The a priori 2-tailed point biserial model sample size calculation was performed using the G*Power software (version 3.1; Franz Faul, Kiel University, Germany) considering a coefficient of determination of .609 obtained from a previous similar study,³¹ with alpha set at 5% and the sampling power (1−β) set at 95%. A sample size of 37 subjects was returned, and the actual power was .9505. The exclusion criteria were as follows: (1) injury on the lower limbs during the past 6 months; (2) Diagnostic of hip and knee osteoarthritis; (3) Previous knee surgery; (4) Neurologic disorder diagnosis (stroke, and/or head trauma); (5) Symptoms related to the hip and knee area. All tests took place at the Musculoskeletal Lab in the Federal University of Juiz de Fora—Campus Governador Valadares. The Federal University of Juiz de Fora ethics committee for human investigation approved the procedures employed in the study (registry number 65024022.4.0000.5147). The objectives, benefits, and potential risks involved were previously explained to all participants. Then, all participants signed the informed consent form prior to participation. Participants were recruited from July to August/2022.

Equipment

The BTrackS Balance Plate (Balance Tracking System, San Diego, CA, USA) was used to assess balance. The force platform (40 × 60 cm, with a sampling frequency of 25 Hz) have four strain gauges implanted on the corners to determine the center-of-pression (COP) length distance. Previous studies showed that the BTrackS sampling frequency satisfied the Nyquist theorem for the slow (<10 Hz) COP changes measured in the present study.^32,33 Previous work has shown BTrackS to perform with the same accuracy/precision as a laboratory-grade force platform.^32,33 Prior to testing, the force platform was leveled using four adjustable screws-legs, and connected to the computer through a USB cable. The power to the platform was also provided by the USB cable.

The WBB (Wii Fit® platform, Nintendo, Japan) was positioned on the top of the force platform. The WBB was paired to a laptop using the Bluetooth connection. The BRAINBLOX custom freeware (version 1.0; University of Colorado Boulder, Colorado, EUA) collected and extracted the raw data from each WBB transducer. Prior to data collection, the calibration of the WBB was performed using a previously described method of applying multiple loads, creating a scale for data correction.¹⁸ The calibration proceeded by applying progressive loads ranging from 0 to 45 kg on each sensor individually. Then, a regression equation of raw values and the known loads converted the raw sensor data to corrected force values.

Procedure

Each testing session was held in an isolated space with limited distractions. Each participant was asked to perform the mCTSIB, consisting of four, 20-s trials to assess the ability to control body sway while the sensory feedback was systematically managed. For each trial, the participant was asked to stand still on the set-up system (WBB on the force platform) with both hands on the hips and feet shoulder width apart, barefoot, looking straightly to a target 2-m away from the set-up system. A 15-s pause was allowed between trials. A tone set the beginning and the end of each trial. The sensory feedback was manipulated by closing eyes and/or standing on a foam cushion. A standard thermoplastic elastomer foam cushion (ProsourceFit, Chatsworth, California, USA [31 × 6 × 20 cm]) was used on the WBB when applicable. The order of the trials remained the same across all testing session (Figure 1): (1) Firm surface with opened-eyes (EO); (2) Firm surface with closed-eyes—proprioception condition (EC); (3) Foam cushion with opened-eyes—visual condition (EO+); and (4) Foam cushion with closed-eyes—vestibular condition (EC+). The mCTSIB result was based on the COP path length from the forces simultaneously placed on the WBB and on the force platform during standing.

Figure 1.

The four testing trial conditions. The individual depicted in this figure was not a study participant and gave informed consent for use of her likeness. Each trial requires individuals to stand as still as possible on the system (Wii balance board + force platform) with feet shoulder width and hands on hips. (a) Open while standing on the firm plate surface; (b) eyes closed while standing on the firm plate surface; (c) eyes open while standing on a compliant foam cushion; and (d) eyes closed while standing on a compliant foam cushion.

Data extraction

The BTrackS Assess Balance software calculated the force platform results for each trial. The average total COP path length was displayed in centimeters (cm). The force data were transferred from the WBB to a personal laptop at 50 Hz. To analyze the data, a single file of each participant was opened using the Excel software (version 2023; Microsoft Corporation, Redmond, WA, USA). The sheet contained eight columns. The sheet information was interpreted as the following guide: column A: time in milliseconds since the software was running; column B: the force output obtained from the top left corner sensor; column C: the force output obtained from the top right corner sensor; column D: the force output obtained from the bottom left corner sensor; column E: the force output obtained from the bottom left sensor (all force sensors displayed their data in kilograms); column F: the COP distance from the force platform center in the x axis-direction; column G: the COP distance from the center of the platform in the y axis-direction (the column F and G displayed their data in centimeters); column H: The total force output (i.e., the sum of the values extracted from the columns 2 to 5), in kilograms. All values expressed in kilogram force were transformed to Newtons using the notation: 1 kgf = 9.80665 N.

The path length was determined for both WBB and force platform by first quantifying the distance between successive registered COP locations according to the following formula

Distance = {({[{COPx}_{2} - {COPx}_{1}]}^{2} + {[{COPy}_{2} - {COPy}_{1}]}^{2})}^{0.5}

where COPx₂ and COPx₁ are adjacent time-points in the COPx (medial/lateral) time series, and COPy₂ and COPy₁ are adjacent time-points in the COPy (anterior/posterior) time series. The sum of all distances was then added together to obtain the total path length.

Statistical analysis

Data were presented as mean (SD). The Shapiro–Wilk test was used to test the Gaussian distribution. As the normality was accepted, the two-way mixed-effects model intraclass correlation coefficient (ICC) was used to evaluate the agreement and consistency between results. The Cronbach α test assessed the expected correlation measuring the same construct. The qualitative classification of the ICC and Cronbach α values was as follows: poor (<.50), moderate (.5–.75), good (.75–.90), or excellent (>.90). Linear regression returned the Pearson’s coefficient of correlation (r) along with the adjusted coefficient of determination (r²). A qualitative classification was also used to estimate the correlation coefficients: high (≥.70), moderate (.50–.70), low (.30–.50), and weak (<.30). The Bland–Altman method was used to estimate the measures biases, and the between-result lower and upper limits of agreement. The standard error of measurement, the percentage of SEM as a coefficient of variation (%SEM = SEM × 100/mean), and the minimal detectable change (MDC) were calculated at a 95% confidence level (MDC = SEM × 1.96 × √2). The mean difference between WBB and force platform was used to set the significance considering the MDC. A %SEM of 10% or less was set as the level at which a measure was considered reliable. The significance was set at p < .05. All statistics were performed using the JAMOVI software (The Jamovi project (2022). JAMOVI (Version 2.3) [Computer Software]. Retrieved from https://www.jamovi.org at 20/03/2023).

Results

Descriptive data and the detailed results were presented in Table 1. The ICC were all above .98, considering both agreement and consistency. Also, the Cronbach alfa ranged from .993 to .997. Those results were qualitatively classified as excellent for all comparisons. The correlation was classified as high (r > .98; p = .001), with excellent adjusted coefficients of determination (.97 < r² < .99). Bland–Altman method showed high levels of agreement between WBB and force platform (Figure 2). For each condition EO, EC, EO+, and EC+ the SEM analysis showed .10, .11, .10, .18 cm of displacement, and the MDC analysis returned .27, .30, .29, and .50 cm of displacement, respectively. The mean differences were 1.36, 1.54, 1.20, and 2.41 cm, respectively, for each condition. The percentages of SEM values were, also respectively, .60, .50, .32, and .30%.

Table 1.

WBB versus force platform validity analysis.

Condition	COP PL, cm		ICC (agreement)	ICC (consistency)	Cronbach α	r	r²
Condition	Force platform	WBB	ICC (agreement)	ICC (consistency)	Cronbach α	r	r²
EO	16.84 (5.79)	18.14 (5.95)	.961	.986	.993	.987	.973
EC	22.78 (9.39)	24.30 (9.63)	.982	.995	.997	.995	.990
EO+	32.38 (9.90)	33.56 (10.20)	.982	.988	.994	.989	.978
EC+	57.08 (21.54)	59.43 (22.76)	.987	.993	.997	.995	.989

EO: opened-eyes; EC: firm surface with closed-eyes – proprioception condition; EO+: foam cushion with opened-eyes—visual condition; EC+: foam cushion with closed-eyes—vestibular condition; WBB: Wii balance board; ICC: intraclass correlation coefficient; r: coefficient of correlation; r²: coefficient of determination.

Figure 2.

Bland–Altman plots. (a) Open eyes—firm surface: Bias = 1.360 (95% CI, 1.09 to 1.63), LLA = −0.529 (95% CI, −1.00 to −0.06), ULA = 3.25 (95% CI, 2.78 to 3.72); (b) Closed eyes—firm surface: bias = 1.54 (95% CI, 1.26 to 1.82), LLA = −0.37 (95% CI, −0.84 to 0.11), ULA = 3.44 (95% CI, 2.97 to 3.92); (c) Open eyes—foam surface: bias = 1.20 (95% CI, 0.76 to 1.64), LLA = −1.82 (95% CI, −2.57 to −1.06), ULA = 4.22 (95% CI, 3.46 to 4.97); and (d) Closed eyes—foam surface: bias = 2.41 (95% CI, 1.66 to 3.16), LLA = −2.71 (95% CI, −4.01 to −1.42), ULA = 7.53 (95% CI, 6.24 to 8.82). CI indicates confidence interval; LLA, lower limit of agreement; ULA, upper limit of agreement.

Discussion

All findings suggest the WBB as a valid device to perform the instrumented mCTSIB. The excellent results from the Cronbach’s α coefficient, and the ICC showed both, agreement and consistency between measures comparing WBB and the force platform. The high values obtained from the linear regression showed excellent coefficient levels of correlation and determination. The agreement was also shown using the Bland-Altman method, with low bias and the majority of the results scattered between the lower and upper levels of agreement. The low values of SEM were also excellent results, as the SEM is a measure of how measured test scores (in this case, WBB values) are spread around a true score (Force platform values). The %SEM were all below 10%, indicating small variation between WBB and force platform values. Finally, the MDC values would determine the smallest change in a measurement that can be considered significant. Changes of at least MDC values cannot be considered a measurement error, but a true change. In this case, the results were relevant considering the mean difference of each comparison, and the highest occurred during the closed eyes condition on the foam surface (EC+). This result may be due to a more challenging vestibular condition, as the participants had to deal with simultaneous visual (eyes closed) and unstable (foam surface) perturbations.¹³

As previously above mentioned, the WBB was widely tested against the gold-standard force platforms in several distinct health conditions, showing excellent results on distinct test modalities, as bipodal, unipodal, limits of balance, with open and closed eyes.^{18–20,23,24,27–29} However, only two studies have focused on the WBB validity during the mCTSIB. The 1^st study compared the WBB against a force platform using a sample of 37 older adults.³¹ However, the authors did not provide any sample size calculation, nor the cushion brand used to assess the balance challenging the proprioception system. Also, the SEM (7.3 to 13.9%) and the MDC (19.9 to 38.5%) were higher compared to the present results. Despite those limitations, the conclusions were similar to the present study, confirming the WBB validity to perform the mCTSIB. An important issue is that older adults often show co-morbidities that might exert influence on the balance results, such as diabetes, musculoskeletal, polypharmacy, cardiac and neurologic diseases, visual and vestibular impairment,^34–36 limiting the study’s external validity. In the 2^nd study,³⁷ the authors developed a dedicated software to extract data from the WBB. They also used a force platform as the gold-standard device to compare the results of 18 healthy adults. Again, no sample size calculation was provided. The authors did not show any ICC value, SEM or MDC, limiting the conclusions to the Bland–Altman, the coefficients of correlation and determination. The conclusions may then be impaired due to those limitations.

Studies have examined instrumented versions of the mCTSIB on different platforms.^38–40 A study assessed the mCTSIB using the Balance Master and demonstrated substantial to excellent intra- and inter-rater reliability in community-dwelling women.³⁸ Another study investigated the mCTSIB on the Fall Risk Assessment System and demonstrated good interrater reliability.³⁹ The Biodex Balance System was used in a study that evaluated the mCTSIB in a large sample of older women. Test–retest reliability was assessed in a subsample of 24 participants after a 7-days interval, demonstrating moderate reliability, with an ICC of 0.628.⁴⁰ These findings highlight that different posturographic platforms, have been used to instrument the mCTSIB, and support the rationale for exploring the WBB as a low-cost and portable alternative.

The present study used the BTrackS System as the gold-standard device to validate the WBB as a standard device for the mCTSIB. The intention was to allow the comparison between WBB results and the normative values obtained using the mCTSIB.^6,15 Also, the cushion foam on top of the WBB and FP did not affect the results. Thus, both devices were sensitive detecting the patterns of the COP when proprioceptive input was challenged. The same behavior was observed in previous studies using similar set-up.^31,37

The WBB validity to assess the mCTSIB would allow health professionals and coaches to objectively evaluate balance in distinct aspects and conditions with less complexity, following an operational procedure, and as no previous extensive training is required. Minimal investment is also an advantage, as the WBB is inexpensive compared to other gold-standard force platforms. Quantifying the COP displacements might help to improve the tests’ sensitivity, detecting possible impairments more precisely, such as poor use of surface cues, poor gaze stabilization, and poor use of vestibular inputs during testing conditions.³¹

Some limitations of the present study must be addressed. The present study included only healthy and young participants, a convenience sample. Any pathological or associated comorbidities could change the assessed primary outcome. However, the present study avoided any adverse outcome due during repeated trials, so the safety of the assessment would be set. The data obtained in young people can be used as a reference for future studies with older adults or individuals with balance impairments. Thus, the sample was entirely composed by non-pathological participants. The WBB was officially discontinued in 2017, however, the console and its accessories remain available on the market, including through second-hand sales, which sustains its feasibility for research and clinical applications. More importantly, the significance of this study extends beyond the specific use of the WBB itself. By demonstrating the potential of an affordable and widely accessible technology, the findings of the present study may encourage the development of new low-cost devices with similar principles, broadening opportunities for assessment and intervention. In this sense, our work not only highlights the value of the WBB but also underscores the broader need for accessible and sustainable solutions in both research and clinical practice.

Conclusions

The current results suggest the validity of WBB for the mCTSIB in healthy young adults. The cost-effectiveness, the user-friendly interface, and the WBB portability provide an effective form to assess the distinct aspects of the balance during the mCTSIB.

Footnotes

ORCID iD

Alexandre Carvalho Barbosa

Ethical considerations

The Federal University of Juiz de Fora ethics committee for human investigation approved the procedures employed in the study (registry number 65024022.4.0000.5147).

Author contributions

CONCEPTION: M.E.H.S, A.C.B; PERFORMANCE OF WORK: M.E.H.S, M.A.O, R.S.H.M; INTERPRETATION OR ANALYSIS OF DATA: K.R.F, M.C.G.S.M, M.A.B, A.C.B; PREPARATION OF THE MANUSCRIPT: M.E.H.S, M.A.O, R.S.H.M, K.R.F, M.C. G.S.M, M.A.B, A.C.B; REVISION FOR IMPORTANT INTELLECTUAL CONTENT: M.E.H.S, A.C.B; SUPERVISION: K.R.F, M.C. G.S.M, M.A.B, A.C.B.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Throughout the duration of this study, the principal investigator received financial support from the Coordination for the Improvement of Higher Education Personnel (CAPES)—Code 001 and from the Research Support Foundation of the State of Minas Gerais (FAPEMIG)—APQ 02040-18.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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