Informing wobble-board training and assessment through an investigation of the effect of biological-sex,anthropometrics,footwear and dual-tasking in young adults

Abstract

BACKGROUND:

Despite wobble board use being common in physiotherapy the effect of certain factors, essential to clinical reasoning, have not been investigated.

OBJECTIVE:

To determine the effect of biological sex, anthropometrics, footwear and dual tasking (DT) on wobble board balance performance.

METHODS:

Eighty-six healthy participants (44 females) had their wobble board performance measured during double-leg-stance (DLS) with eyes open (DLSEO), closed (DLSEC) and single-leg-stance (SLS) tasks, with and without footwear and a DT added. Anthropometrics were also measured.

RESULTS:

Females outperformed males during most tasks, with some large effect sizes (ES). Performance was moderately related to weight and shoulder, waist and hip circumference. Overall, there were no differences between footwear and no footwear, except for males during SLS. DT made little difference, except during DLSEO and SLS, where single task was better than DT, though only females had a large ES.

CONCLUSION:

During wobble board tasks, biological sex differences were observed and a modest correlation between anthropometrics and performance noted. DT and footwear had minimal effect.

Keywords

Wobble board dual task footwear gender correlation

1. Introduction

The use of dynamic balance platforms, such as wobble boards, is commonplace within clinical practice and training facilities, however, there is growing interest in using wobble boards for assessment purposes. The efficacy of wobble board training has been demonstrated for the rehabilitation of injuries [1], reducing injury risk [2] and improving neuromuscular function [1], however wobbleboard performance i.e., how well an individual can perform a wobbleboard task, is not considered in the literature. There are many factors that influence balance performance in the literature e.g., footwear, however, it is not clear if these factors should be a consideration with respect to measurement of actual performance on a wobble board.

To date, reliability and validity of wobble board performance measurement has been established [3, 4, 5, 6]. However, several key fundamental issues remain unresolved, thus, impairing the standardisation of wobble board use. Extrapolating from the balance literature, these include, consideration of the effects of biological sex, anthropometric characteristics, the wearing or not of footwear and the relative effect of single and dual tasking.

1.1 Biological sex and anthropometry

It is not understood whether there are differences in expected performance between females and males. Previous studies have demonstrated potential differences in balance between the biological sexes [7], however, some authors have argued that these are merely the expression of differing anthropometrics [7, 8]. Therefore, the extent of the real impact of biological sex remains confused and it is not clear whether performance should be compared to females or males, or a combined cohort. Since the comparing of normative databases or ‘clinical norms’ is commonplace, determining the correct cohort for comparison is critical for identifying impairments. Therefore, when using a wobble board as an assessment tool, whether clinicians should compare performance scores to same sex cohorts or mixed cohorts remains unknown. Despite this uncertainty, to the best of the authors’ knowledge, no studies have systematically assessed wobble board performance in females and males and explored its relationship with multiple anthropometric variables.

1.2 Footwear or no footwear

It has been established that footwear has the capacity to affect dynamic balance [9]. However, the fundamental question of whether footwear impacts wobble board performance remains unknown. A previous study using a rocker board (single axis wobble board) demonstrated that footwear made no difference to performance [9] and this was supported by a study utilising a foam surface [10]. However, to date, no study has explored this using a wobble board. Therefore, it remains unclear for the clinician whether footwear influences wobble board performance and this information is essential in underpinning the clinical reasoning behind whether assessment and training should be completed in footwear or not.

1.3 Primary and secondary tasking

It is known that the addition of a cerebral task, whilst balancing, affects balance performance [11, 12] and such an approach is gaining in popularity for balance assessment. However, its effect on wobble board performance and training has yet to be explored. It appears that the greatest effect is in cognitively impaired older adults, with the effect in younger, non-cognitively impaired adults being less clear [13]. Therefore, there is uncertainty regarding the real impact of adding a cognitive task (dual tasking) on wobble board performance and this information is important for designing clinical assessment and rehabilitation programs, including those using a wobble board.

This study aims to understand the effect of biological sex, anthropometrics, footwear and dual tasking on wobble board performance. This will be achieved by:

Determining if there are female/male differences in wobble board performance.

Exploring the relationship between anthropometrics and wobble board performance.

Determining if wearing footwear affects wobble board performance.

Determining if dual tasking influences wobble board performance.

This study will be the first of its kind to systematically identify critical elements, which may affect wobble board performance. This information will result in a significant contribution to clinical reasoning around wobble board performance assessment and training prescription, providing for the first time, clarity over which factors influence wobble board performance.

2. Materials and methods

2.1 Design

This study utilised an observational design.

2.2 Participants

Forty-four healthy females (mean age 22.2 $\pm$ 1.0 years, height 1.596 $\pm$ 0.059 m, weight 62.5 $\pm$ 12.3 Kg, and BMI 24.4 $\pm$ 4.2 Kg/m²) and 42 healthy males (mean age 22.0 $\pm$ 1.2 years, height 1.741 $\pm$ 0.083 m, weight 78.3 $\pm$ 23.8 Kg and BMI 25.8 $\pm$ 7.6 Kg/m²) were enrolled in this study. Participants were recruited via media advertisements at two institutions (College of Medical Science and College of Health and Rehabilitation Sciences at King Saud University, Prince Sattam bin Abdulaziz University and Princess Nourah bint Abdulrahman University, Saudi Arabia). The sample size was informed via calculation, employing G power software that indicated 41 individuals per group were required to detect the effect size of Cohen’s $d=$ 0.85 (data from Puszczalowska-Lizis et al. [14]), with an alpha level of 0.004 and a beta of 0.8. Written informed consent was obtained from all participants prior to experimentation. The study follows the principles of the Declaration of Helsinki and was approved by the Princess Nourah bint Abdulrahman University Institutional Human Ethics Committee (H-01-R-059).

Individuals were excluded from the study if they had suffered a lower limb injury, were experiencing lower limb or lower back pain, had a history of surgery, or any disorders or conditions that might affect balance, such as rheumatological or neurological disorders, vestibular conditions, or visual problems, within the last 12 months, or who were pregnant or unwell at the time of testing.

Anthropometric measures were collected during standing, comprising of hip circumference (circumference around the greater trochanters); waist circumference (circumference around the mid-point between the ilium and the umbilicus) and shoulder circumference (circumference inferior to the acromion process) [15]. Based on the obtained measurements, the shoulder/waist ratio (SWR) was calculated by dividing the shoulder circumference by the waist circumference and the shoulder/hip ratio (SHR) by dividing the shoulder circumference by the hip circumference [15]. All anthropometrics were collected by a Physical Therapist with over 10 years of experience. Habitual physical activity was measured using the, previously validated, Baecke questionnaire [16]. This questionnaire is based on a five-point scale that reflects energy expenditure in indicies such as work, sport and leisure time [16].

2.3 Instrumentation

Wobble board performance was measured using a proprioceptive-stabilometric-assessment machine (Pro- kin 252, Technobody Inc, Italy), with integrated sensors and proprietary software, providing digitised data. The Prokin has a circular unstable platform, so operates as an instrumented wobble board. Performance is assessed by measuring an individual’s ability to maintain the board horizontally. The maximum achievable board tilt angle, at the circular center of the Prokin, was 15 degrees, with stability set at the lowest resistance to ensure it tilted freely, with data captured at 20 Hz. This was quantified through measurement of the tilt angle of the board; therefore, the tilt behavior of the Prokin circular center provided the parameters to assess wobble board performance. This device was selected due to established high levels of reliability and validity [17], as well as minimising operator error or bias [18]. Additionally, the Prokin device provides a supportive handrail for safety in case of a loss of balance [19].

2.4 Procedure

Participants were allowed three minutes to become familiarised with specified experimental tasks and the test equipment (Prokin). Three minutes was deemed a good compromise between familiarisation of the task whilst minimising any potential learning effect. The participants were then tested, performing double leg stance eyes open and closed and single leg stance eyes open (dominant leg), for 30 seconds each. To minimised any bias from a learning effect, the sequence of tasks was randomised using a random number generator (www.random.org).

Participants were instructed to maintain the board level at the horizontal to the best of their ability, with their arms positioned freely, wherever comfortable. A V-Shaped marker was used to standardise foot position. A rest period of 60 seconds was provided between each task. Built in safety bars, positioned anteriorly and bilaterally, ensured participant safety [19]. The task was considered a fail if the participant touched the safety bars, touched down with their non-balancing leg or altered their foot position. If a participant failed, two further repeats were allowed. During the experiment, the participants were offered no verbal feedback or coaching. The participant’s wobble board performance was evaluated when barefoot and whilst wearing their own training shoes. All the tasks were repeated as “dual tasks” where the participants were required, in addition to their balance task, to count backwards from 100, sequentially subtracting 7, over 30 seconds. This calculation task is a common dual task that is performed simultaneously during postural tasks [20].

Table 1
Results of wobble board performance as measured by stability index and statistical testing determining if biological sex affects wobble board performance with footwear (shod) and without footwear (unshod) conditions and during dual tasks (median and interquartile range)

	Female APSI^∘		Male APSI^∘				Female MLSI^∘		Male MLSI^∘
Task	Med	IQR	Med	IQR	$p$ -value	ES	Med	IQR	Med	IQR	$p$ -value	ES
Shod
DLSEOS	3.80	2.17	4.36	2.82	0.113	0.51	5.19	2.67	5.82	3.82	0.406	0.35
DLSECS	7.81	3.06	9.96	2.35	0.001^*	1.34	7.65	2.68	9.94	2.09	$<$ 0.001^*	1.40^φ
SLSS	3.66	1.84	4.11	2.64	0.045	0.42	4.99	2.49	5.36	3.33	0.178	0.25
Unshod
DLSEOUS	3.78	1.91	5.38	2.92	0.003^*	0.91^φ	4.75	2.68	5.68	4.01	0.090	0.56
DLSECUS	8.22	2.84	10.12	3.06	0.001^*	1.10^φ	8.13	2.72	9.78	2.26	$<$ 0.001^*	1.15^φ
SLSUS	3.83	2.01	4.19	1.80	0.110	0.37	4.89	3.17	5.38	2.70	0.417	0.33
Dual task
DLSEODTS	4.05	1.97	5.21	3.40	0.013	0.76	5.53	2.83	7.18	4.04	0.245	0.81
DLSECDTS	8.21	2.54	9.45	2.94	0.005	0.96^φ	7.83	2.51	9.78	2.79	0.001^*	1.31^φ
SLSDTS	4.34	1.88	4.53	2.41	0.061	0.19	5.46	2.00	6.55	3.97	0.082	0.61
DLSEODTUS	4.43	2.09	5.04	4.02	0.020	0.42	5.77	2.85	6.73	4.14	0.276	0.54
DLSECDTUS	8.06	3.14	10.13	2.97	$<$ 0.001^*	1.19^φ	8.39	2.25	9.51	2.25	0.004^*	0.90^φ
SLSDTUS	4.12	2.01	4.24	2.41	0.188	0.12	4.98	2.42	5.51	3.40	0.344	0.35

AP-SI; anteroposterior stability index, ML-SI; mediolateral stability index, IQR; interquartile range, DLSEOS; Double leg stance eyes open shod, DLSECS; Double leg stance eyes closed shod, SLSS; Single leg stance shod, DLSEOUS; Double leg stance eyes open unshod, DLSECUS; Double leg stance eyes closed unshod, SLSUS; Single leg stance unshod, DLSEODTS; double leg stance eyes open dual tasking shod, DLSECDTS; double leg stance eyes closed dual tasking shod, SLSDTS; single leg stance dual tasking shod, SLSDTUS; single leg stance dual tasking unshod, DLSEODTUS; double leg stance eyes open dual tasking unshod, DLSECDTUS; double leg stance eyes closed dual tasking unshod, Med; Median, IQR; interquartile range, ^*significant at $p<$ 0.004 level, ES; effect size, ^φeffect size $\geqslant$ 0.9.

2.5 Data processing

Wobble board performance data were captured by the Prokin software, representing the tilt angle across time of the freely tilting center of the Prokin and this was used to generate both a stability index and the percentage time spent at various tilt angle bandings. The stability index, the average absolute tilt angle, was normalised for time, for both the antero-posterior axis and mediolateral axis. The tilt angle bandings were between 0^∘ and 6^∘ absolute tilt, defined as the inner zone and $>$ 6^∘ of absolute tilt as the outer zone, with the percentage time in each zone calculated.

2.6 Statistical analysis

Data were analysed using the Statistical Package for the Social Sciences software (SPSS) for Windows version 26 (IBM Corp., Armonk, NY, USA). Shapiro-Wilk tests were used to assess normality across the entire data set. Due to the non-normally distributed data, Mann-Whitney U tests were used to investigate differences between biological sex, Wilcoxon tests were used to investigate differences between both with footwear versus without footwear conditions as well as single versus dual tasks and Spearman’s correlations to explore the relationships between baseline characteristics and wobble board performance. A Bonferroni correction was applied, due to repeated pairwise comparisons, to reduce the alpha to 0.004 between biological sex and the correlational analyses and 0.008 for single versus dual tasks and with footwear versus without footwear analyses. Furthermore, according to the method of effect size calculation outlined in Ricca and Blaine [21], the effect sizes were calculated with a value of $\geqslant$ 0.9 considered as a large effect size [22].

3. Results

3.1 Biological sex

Females outperformed males across all tests, as measured by stability indices, with statistically significant differences evident for double leg stance eyes closed, in both with footwear and without footwear conditions (see Table 1), with large effect sizes. This was the case for both single and dual task conditions and for both antero-posterior and medio-lateral stability indices.

Table 2
Results of wobble board performance as measured by percentage time in each tilt banding and statistical testing determining if biological sex affects wobble board performance with footwear (shod) and without footwear (unshod) conditions and during dual tasks (median and interquartile range)

Task	Median	IQR	Median	IQR	$p$ -value	ES	Median	IQR	Median	IQR	$p$ -value	ES
	Female		Male				Female		Male
	inner time (%)		inner time (%)				outer time (%)		outer time (%)
Shod
DLSEOS	16	23	19	26	0.151	0.29	85	22	81	25	0.123	$-$ 0.33
DLSECS	3	6	2	3	0.058	$-$ 1.00^φ	97	5	99	4	0.082	1.00^φ
SLSS	9	23	14	18	0.134	0.39	92	23	87	18	0.145	$-$ 0.48
Unshod
DLSEOUS	17	23	17	28	0.762	0.00	83	22	84	28	0.762	0.11
DLSECUS	4	6	2	6	0.135	$-$ 0.75	97	6	98	5	0.299	0.50
SLSUS	12	26	19	19	0.181	0.59	89	26	82	20	0.192	$-$ 0.54
Dual tasking
DLSEODTS	9	12	10	21	0.259	0.19	91	13	91	21	0.309	$-$ 0.07
DLSECDTS	2	5	2	4	0.546	0.00	98	5	98	3	0.580	0.00
SLSDTS	6	15	9	18	0.122	0.41	95	15	92	18	0.144	$-$ 0.44
DLSEODTUS	9	11	14	23	0.303	0.56	92	10	87	24	0.278	$-$ 0.59
DLSECDTUS	3	4	1	4	0.416	$-$ 1.32^φ	98	3	99	4	0.384	0.99^φ
SLSDTUS	6	13	16	21	0.001^*	0.97^φ	95	13	84	20	0.001^*	$-$ 1.02^φ

IQR; interquartile range, %inner time; percentage of time tilt in inner zone, %outer time; percentage of time tilt in outer zone, DLSEOS; Double leg stance eyes open shod, DLSECS; Double leg stance eyes closed shod, SLSS; Single leg stance shod, DLSEOUS; Double leg stance eyes open unshod, DLSECUS; Double leg stance eyes closed unshod, SLSUS; Single leg stance unshod, DLSEODTS; double leg stance eyes open dual tasking shod, DLSECDTS; double leg stance eyes closed dual tasking shod, SLSDTS; single leg stance dual tasking shod, SLSDTUS; single leg stance dual tasking unshod, DLSEODTUS; double leg stance eyes open dual tasking unshod, DLSECDTUS; double leg stance eyes closed dual tasking unshod, Med; Median, IQR; interquartile range, ^*significant at $p<$ 0.004 level, ES; effect size, ^φeffect size $\geqslant$ 0.9.

No statistically significant differences were determined between male and female for wobble board performance as measured by percentage time spent in each tilt angle banding, with footwear or without footwear or single or dual tasking, with the exception of single leg stance without footwear dual tasking (see Table 2), where males performed better. In addition, large effect sizes were observed for double leg stance eyes closed, with footwear and without footwear, dual tasking, where females performed better than males.

Table 3

Spearman’s rho ( $r$ ) correlation between wobble board performance (stability index) and anthropometric characteristics

	Height (cm) $r$	Weight (Kg) $r$	Shoulder circumference (cm) $r$	Waist circumference (cm) $r$	Hip circumference (cm) $r$	Shoulder- Waist Ratio (cm) $r$	Shoulder- Hip Ratio (cm) $r$	Physical Activity $r$
Shod
DLSEOS APSI (^∘)	0.367^*	0.678^*	0.529^*	0.560^*	0.579^*	$-$ 0.486^*	$-$ 0.075	0.101
DLSEOS MLSI (^∘)	0.326^*	0.639^*	0.391^*	0.496^*	0.590^*	$-$ 0.501^*	$-$ 0.251	0.109
DLSEOUS APSI (^∘)	0.522^*	0.667^*	0.586^*	0.591^*	0.469^*	$-$ 0.477^*	0.090	0.147
DLSEOUS MLSI (^∘)	0.445^*	0.641^*	0.472^*	0.552^*	0.493^*	$-$ 0.500^*	$-$ 0.059	0.166
DLSECS APSI (^∘)	0.484^*	0.625^*	0.560^*	0.570^*	0.517^*	$-$ 0.491^*	0.012	0.208
DLSECS MLSI (^∘)	0.557^*	0.615^*	0.585^*	0.586^*	0.401^*	$-$ 0.446^*	0.108	0.221
Unshod
DLSECUS APSI (^∘)	0.458^*	0.659^*	0.556^*	0.621^*	0.504^*	$-$ 0.557^*	$-$ 0.006	0.103
DLSECUS MLSI (^∘)	0.464^*	0.595^*	0.551^*	0.554^*	0.421^*	$-$ 0.450^*	0.097	0.125
SLSS APSI (^∘)	0.287	0.561^*	0.410^*	0.431^*	0.441^*	$-$ 0.354^*	$-$ 0.005	0.207
SLSS MLSI (^∘)	0.281	0.528^*	0.390^*	0.428^*	0.502^*	$-$ 0.381^*	$-$ 0.153	0.127
SLSUS APSI (^∘)	0.311^*	0.652^*	0.465^*	0.514^*	0.532^*	$-$ 0.442^*	$-$ 0.087	0.206
SLSUS MLSI (^∘)	0.235	0.406^*	0.292	0.377^*	0.340^*	$-$ 0.360^*	$-$ 0.101	$-$ 0.048
Dual task
DLSEODTS APSI (^∘)	0.409^*	0.602^*	0.510^*	0.539^*	0.563^*	$-$ 0.439^*	$-$ 0.083	0.131
DLSEODTS MLSI (^∘)	0.327^*	0.577^*	0.426^*	0.429^*	0.525^*	$-$ 0.373	$-$ 0.139	0.165
DLSEODTUS APSI (^∘)	0.415^*	0.572^*	0.507^*	0.546^*	0.480^*	$-$ 0.453^*	0.008	0.152
DLSEODTUS MLSI (^∘)	0.312^*	0.562^*	0.460^*	0.428^*	0.473^*	$-$ 0.306^*	$-$ 0.036	$-$ 0.011
DLSECDTS APSI (^∘)	0.369^*	0.649^*	0.550^*	0.629^*	0.570^*	$-$ 0.569^*	$-$ 0.055	0.157
DLSECDTS MLSI (^∘)	0.497^*	0.591^*	0.609^*	0.534^*	0.426^*	$-$ 0.358^*	0.124	0.107
DLSECDTUS APSI (^∘)	0.465^*	0.665^*	0.612^*	0.665^*	0.554^*	$-$ 0.581^*	0.010	0.072
DLSECDTUS MLSI (^∘)	0.479^*	0.597^*	0.489^*	0.535^*	0.411^*	$-$ 0.488^*	0.025	0.091
SLSDTS APSI (^∘)	0.285	0.557	0.454^*	0.406^*	0.521^*	$-$ 0.270	$-$ 0.055	0.276
SLSDTS MLSI (^∘)	0.357^*	0.476^*	0.369^*	0.350^*	0.374^*	$-$ 0.280	$-$ 0.039	0.018
SLSDTUS APSI (^∘)	0.342^*	0.456^*	0.310^*	0.309^*	0.358^*	$-$ 0.264	0.000	0.205
SLSDTUS MLSI (^∘)	0.269	0.558^*	0.378^*	0.477^*	0.496^*	$-$ 0.459^*	$-$ 0.179	$-$ 0.037

APSI; Anteroposterior stability index, MLSI; Mediolateral stability index, r; spearman’s rho correlation, DLSEOS; double leg stance eyes open shod, DLSEODTS; double leg stance eyes open dual tasking shod, DLSECS; double leg stance eyes closed shod, DLSECDTS; double leg stance eyes closed dual tasking shod, SLSS; single leg stance Shod, SLSDTS; single leg stance dual tasking shod, SLSUS; single leg stance unshod, SLSDTUS; single leg stance dual tasking unshod, DLSEOUS; double leg stance eyes open unshod, DLSEODTUS; double leg stance eyes open dual tasking unshod, DLSECUS; double leg stance eyes closed unshod, DLSECDTUS; double leg stance eyes closed dual tasking unshod, ^*significant at $p\leqslant$ 0.004 level.

3.2 Anthropometry

Weight, waist circumference, shoulder circumference, height, hip circumference and shoulder-waist ratio demonstrated moderate correlations with wobble board performance, as measured by stability indices across all tasks. The strongest correlations were observed for weight, with most correlations being greater than 0.55 (see Table 3).

Table 4
Spearman’s rho ( $r$ ) correlation between wobble board performance (tilt banding) and anthropometric characteristics

	Height (cm) $r$	Weight (Kg) $r$	Shoulder circumference $r$	Waist circumference (cm) $r$	Hip circumference (cm) $r$	Shoulder- Waist Ratio (cm) $r$	Shoulder- Hip Ratio (cm) $r$	Physical Activity $r$
Shod
DLSEOS inner time (%)	$-$ 0.104	$-$ 0.499^*	$-$ 0.202	$-$ 0.329^*	$-$ 0.549^*	0.385^*	0.388^*	0.050
DLSEOS outer time (%)	0.089	0.489^*	0.193	0.320^*	0.545^*	$-$ 0.377^*	$-$ 0.395^*	$-$ 0.055
DLSECS inner time (%)	$-$ 0.407^*	$-$ 0.576^*	$-$ 0.463^*	$-$ 0.491^*	$-$ 0.485^*	0.422^*	0.073	$-$ 0.173
DLSECS outer time (%)	0.386^*	0.584^*	0.475^*	0.476^*	0.512^*	$-$ 0.391^*	$-$ 0.083	0.253
SLSS inner time (%)	$-$ 0.041	$-$ 0.297	$-$ 0.092	$-$ 0.104	$-$ 0.340^*	0.122	0.268	0.137
SLSS outer time (%)	0.047	0.282	0.077	0.092	0.314^*	$-$ 0.114	$-$ 0.257	$-$ 0.138
Unshod
DLSEOUS inner time (%)	$-$ 0.309^*	$-$ 0.543^*	$-$ 0.355^*	$-$ 0.434^*	$-$ 0.458^*	0.399^*	0.120	$-$ 0.058
DLSEOUS outer time (%)	0.304^*	0.539^*	0.349^*	0.435^*	0.452^*	$-$ 0.408^*	$-$ 0.122	0.072
DLSECUS inner time (%)	$-$ 0.242	$-$ 0.464^*	$-$ 0.319^*	$-$ 0.407^*	$-$ 0.427^*	0.425^*	0.125	0.001
DLSECUS outer time (%)	0.197	0.439^*	0.275	0.358^*	0.437^*	$-$ 0.389^*	$-$ 0.180	$-$ 0.026
SLSUS inner time (%)	$-$ 0.070	$-$ 0.389^*	$-$ 0.178	$-$ 0.270	$-$ 0.405^*	0.272	0.247	0.105
SLSUS outer time (%)	0.075	0.390^*	0.173	0.273	0.406^*	$-$ 0.280	$-$ 0.250	$-$ 0.103
Dual task
DLSEODTS inner time (%)	$-$ 0.117	$-$ 0.353^*	$-$ 0.160	$-$ 0.165	$-$ 0.422^*	0.144	0.274	0.046
DLSEODTS outer time (%)	0.125	0.356^*	0.165	0.165	0.417	$-$ 0.140	$-$ 0.261	$-$ 0.035
DLSECDTS inner time (%)	$-$ 0.210	$-$ 0.458^*	$-$ 0.337^*	$-$ 0.385^*	$-$ 0.481^*	0.350^*	0.210	0.049
DLSECDTS outer time (%)	0.191	0.451^*	0.347^*	0.345^*	0.489^*	$-$ 0.278	$-$ 0.214	0.027
SLSDTS inner time (%)	$-$ 0.012	$-$ 0.291	$-$ 0.097	$-$ 0.053	$-$ 0.314^*	0.025	0.208	0.100
SLSDTS % outer time	0.020	0.290	0.108	0.060	0.311^*	$-$ 0.027	$-$ 0.196	$-$ 0.125
DLSEODTUS inner time (%)	$-$ 0.101	$-$ 0.410^*	$-$ 0.272	$-$ 0.232	$-$ 0.414^*	0.140	0.146	0.114
DLSEODTUS outer time (%)	0.104	0.410^*	0.271	0.235	0.409^*	$-$ 0.142	$-$ 0.137	$-$ 0.116
DLSECDTUS inner time (%)	$-$ 0.230	$-$ 0.546^*	$-$ 0.370^*	$-$ 0.414^*	$-$ 0.512^*	0.382^*	0.194	0.133
DLSECDTUS outer time (%)	0.255	0.561^*	0.383^*	0.438^*	0.517^*	$-$ 0.401^*	$-$ 0.184	$-$ 0.127
SLSDTUS inner time (%)	0.103	$-$ 0.178	0.081	0.044	$-$ 0.263	0.008	0.325^*	0.089
SLSDTUS outer time (%)	$-$ 0.104	0.156	$-$ 0.094	$-$ 0.064	0.232	0.016	$-$ 0.308^*	$-$ 0.082

% Inner time; percentage of time tilt in inner zone, % outer time; percentage of time tilt in outer zone, r; spearman’s rho correlation, DLSEOS; double leg stance eyes open shod, DLSEODTS; double leg stance eyes open dual tasking shod, DLSECS; double leg stance eyes closed shod, DLSECDTS; double leg stance eyes closed dual tasking shod, SLSS; single leg stance Shod, SLSDTS; single leg stance dual tasking shod, SLSUS; single leg stance unshod, SLSDTUS; single leg stance dual tasking unshod, DLSEOUS; double leg stance eyes open unshod, DLSEODTUS; double leg stance eyes open dual tasking unshod, DLSECUS; double leg stance eyes closed unshod, DLSECDTUS; double leg stance eyes closed dual tasking unshod, ^*significant at $p\leqslant$ 0.004 level.

Similar findings were evident for the percentage time in various tilt angle bandings, where weight and hip circumference demonstrated moderate correlations with almost all tasks and again the strongest correlations were observed with weight (see Table 4).

Table 5

Results of significance testing and effect size calculation for the effect of being with footwear or without footwear on wobble board performance

	DLSEO with footwear vs without footwear		DLSEC with footwear vs without footwear		SLS with footwear vs without footwear
	$p$ -value	Effect size	$p$ -value	Effect size	$p$ -value	Effect size
Female
APSI (^∘)	0.530	$-$ 0.03	0.852	0.30	0.360	0.17
MLSI (^∘)	0.111	$-$ 0.34	0.958	0.39	0.843	$-$ 0.07
Inner time (%)	0.084	0.10	0.435	0.20	0.346	0.18
Outer time (%)	0.088	$-$ 0.15	0.504	0.00	0.335	$-$ 0.27
Male
APSI (^∘)	0.035	0.60	0.626	0.12	0.005^*	0.07
MLSI (^∘)	0.970	$-$ 0.07	0.970	$-$ 0.15	0.150	0.02
Inner time (%)	0.300	$-$ 0.23	0.792	0.33	0.187	0.51
Outer time (%)	0.255	0.34	0.917	$-$ 0.33	0.178	$-$ 0.44

DLSEO; double leg stance eyes open, DLSEC; double leg stance eyes closed, SLS; single leg stance, APSI; anteroposterior stability index, MLSI; mediolateral stability index, %inner time; percentage of time tilt in inner zone, %outer time; percentage of time tilt in outer zone, ^*significant at $p\leqslant$ 0.008 level, ^φeffect size $\geqslant$ 0.9.

3.3 Footwear vs without footwear

There were no significant differences in wobble board performance between the footwear and without footwear conditions in females or males, regardless of the task or metric except single leg stance for antero-posterior stability indices in males. In addition, no large effect sizes were observed (see Table 5).

Table 6
Results of significance testing and effect size calculation for the effect of single and dual tasking on wobble board performance

	With footwear single task vs dual task						Without footwear single task vs dual task
	DLSEO		DLSEC		SLS		DLSEO		DLSEC		SLS
	$p$ -value	Effect size	$p$ -value	Effect size	$p$ -value	Effect size	$p$ -value	Effect size	$p$ -value	Effect size	$p$ -value	Effect size
Female
APSI (^∘)	0.163	$-$ 0.27	0.713	$-$ 0.27	0.014	$-$ 0.66	0.154	$-$ 0.69	0.762	0.11	0.066	$-$ 0.30
MLSI (^∘)	$<$ 0.001^*	$-$ 0.26	0.093	$-$ 0.13	0.092	$-$ 0.41	0.001^*	$-$ 0.86	0.140	$-$ 0.22	0.762	$-$ 0.06
Inner time (%)	$<$ 0.001^*	0.64	0.475	0.50	0.016	0.46	$<$ 0.001^*	0.91^φ	0.073	0.20	0.004^*	0.59
Outer time (%)	$<$ 0.001^*	$-$ 0.60	0.623	$-$ 0.50	0.021	$-$ 0.44	$<$ 0.001^*	$-$ 0.89	0.195	$-$ 0.20	0.003^*	$-$ 0.63
Male
APSI (^∘)	0.001^*	$-$ 0.65	0.196	0.47	0.009	$-$ 0.33	0.062	0.19	0.371	$-$ 0.01	0.004^*	$-$ 0.06
MLSI (^∘)	$<$ 0.001^*	$-$ 0.75	0.599	0.17	0.038	$-$ 0.77	0.008^*	$-$ 0.54	0.666	0.24	0.442	$-$ 0.09
Inner time (%)	$<$ 0.001^*	0.71	0.697	$-$ 0.33	0.002^*	0.39	0.019	0.31	0.653	0.5	0.240	0.38
Outer time (%)	$<$ 0.001^*	$-$ 0.78	0.696	0.33	0.003^*	$-$ 0.58	0.026	$-$ 0.23	0.398	$-$ 0.5	0.353	$-$ 0.19

DLSEO; double leg stance eyes open, DLSEC; double leg stance eyes closed, SLS; single leg stance, APSI; anteroposterior stability index, MLSI; mediolateral stability index, % inner time; percentage of time tilt in inner zone, % outer time; percentage of time tilt in outer zone, ^*significant at $p\leqslant$ 0.008 level, ^φeffect size $\geqslant$ 0.9.

3.4 Single vs dual task

In females, all double leg eyes open tasks were significantly worse when performed with an additional cognitive task across all metrics, with the exception of antero-posterior stability indices. However, only one large effect size was determined for double leg stance eyes open without footwear (see Table 6). In contrast no significant differences (or large effect sizes) were established for double leg stance eyes closed. During single leg stance a significant difference was found for tilt angle banding percentages but not stability indices, however, no large effect sizes were observed.

In males, with footwear condition all metrics for double leg stance eyes open and single leg stance, except medio-lateral stability indices, were significantly worse during dual tasking. However, no large effect sizes were determined (see Table 6). In contrast, medio-lateral stability indices for double leg stance eyes open without footwear and antero-posterior stability indices for single leg stance without footwear were significantly worse during dual tasking, however, no large effect sizes were determined. The percentage of time spent in the inner and outer tilt angle bands for double leg stance eyes open and single leg stance, with footwear were significantly greater during dual tasking.

4. Discussion

This study aimed to explore the effects of biological sex, anthropometrics, footwear and dual tasking on wobble board balance performance and assessment to provide a foundation for clinical decision-making pertaining to wobble board performance assessment and training.

4.1 Biological sex

Females performed better than males across all wobble board balance performance tests as measured by stability indices, with some very large effect sizes presented. Moderate correlations suggested that participants with lower body mass demonstrated better wobble board performance. Dual tasking and the wearing of footwear had little impact on performance. Differences in performance have been identified between the sexes in previous studies of balance [7, 8], however, the reasons for such differences remain poorly understood. Males have been shown to have greater ankle strength [23], which is usually associated with better balance, and with no differences in ankle muscle fatigability [24] or latency [25] between the sexes. Significant differences have been identified in ankle muscle stiffness [26]. It is possible that the female ankle, being less stiff, affords more movement damping, thus minimising the motion of the wobble board and producing better wobble board performance.

4.2 Anthropometry

It is possible that differences in anthropometrics explain the differences in wobble board performances, for example height [27], with taller individuals having a higher center of mass (COM) potentially creating greater instability. The present study established correlations for height and wobble board performance, however, greater correlations were found for weight and upper torso ‘size’. It is possible that the relatively greater ‘mass’ of the upper body accounts for the differences between females and males, with females possessing a greater mass distribution in the lower body [28, 29] and males, in a relatively larger upper torso. In addition to weight, shoulder, waist and hip circumferential measures show the strongest correlations with wobble board performance. This finding is novel, because no previous study has investigated the correlation between wobble board performance and anthropometric baseline characteristics. These results may be due to the elevated COM, as discussed above but might alternatively be due to the moment functioning around the ‘joint’ of the wobble board. For example, if two individuals of a similar height but different weight were to sway their body by the same distance, then the heavier subject would achieve a greater moment around the ‘wobble board joint’, due to the function of mass multiplied by distance. In addition, larger waist circumference and heavier body weight create a shift in COM position anteriorly [30], causing challenges to proprioception [31], which in combination with a reduced muscle strength [32] and greater fatiguability [33], potentially results in poorer wobble board control.

4.3 Footwear vs without footwear

To the authors’ knowledge the present study represents the first of its kind to explore the effect of footwear on wobble board performance. Such information is of importance to therapists, clinicians and users when deciding how best to complete wobble board training and assessment, with footwear or without footwear. To answer this, first it is essential to determine if performance is different across these conditions. The findings of the present study demonstrate that overall, there were no differences in the performance on the wobble board with footwear or without footwear. Since the input system for balance includes the somatosensory system, it is plausible that the no footwear condition leads to an enhancement in somatosensory feedback, in turn leading to enhanced balance. However, this was not the case in this current study. No direct measurement of the changes in somatosensory input were made and therefore, it is not possible to know if such alterations were evident in the current study, or indeed whether such changes were experienced. Furthermore, it is possible that the alternate feedback systems (visual and vestibular) mediated their feedback contribution, negating the additional contribution from the somatosensory system, resulting in no effect of the barefoot condition.

One exception with the footwear condition was identified for male single leg stance, however, the effect size was very small (0.1). This agrees with a previous study using a rocker board (single axis wobble board), where no difference was determined between the with footwear and without footwear condition [9]. During balancing on a stable surface, movements around the center of mass are likely to be translated to movement in the distribution of plantar foot surface pressure, where this may influence the balance performance. Such a mechanism would not be the same in the wobble board condition, where movements of the center of mass result in forces, which disrupt the equilibrium of the board, therefore, any change in the foot surface interface is likely to have minimal effect. It remains unclear if the mechanisms used to maintain wobble board performance with footwear versus without footwear or with single versus dual tasks are similar, and such analysis is beyond the scope of the current study. It is possible, however, that despite the consistency in performance across conditions, the relative contributions from various balance systems are not similar, though such information (e.g., muscle activation, latency etc.) is unknown.

4.4 Single vs dual task

This was the first study to explore the effect of dual tasking on wobble board performance. Significant differences were determined mainly for double leg stance eyes open amongst the footwear and without footwear conditions, demonstrating poorer performance when dual tasking. Direct comparison with the wobble board literature is not possible, however, it has been demonstrated that balancing on unstable surfaces is affected by counting aloud [12]. Interestingly, Yardley and colleagues [12] challenge the current understanding of dual tasking, where dual task cost is in response to cognitive function, where the balance task cannot be attended to in the same way, due to the attentional demands of the arithmetic. Their study suggests it may be related to the dual function of the muscles needed for postural control and voicing the arithmetic aloud, as no dual task cost was seen for the same mental task without verbalisation. Such a mechanism may be at play here, with the wobble board performance, however, if this were the case then a more universal effect might be expected across all wobble board tasks. With the minimal impact of dual tasking on other tasks, it remains unclear why some were affected, whilst others were not. Furthermore, there is a clear difference between this unstable surface and the Prokin wobble board, as used in this study and small effect sizes overall for dual task cost were observed. Future studies could focus on unravelling the potential mechanisms behind dual task cost during wobble board performance.

This study has made several contributions to the understanding of wobble board performance and assessment. The systematic approach to exploring performance across several conditions offers a strong contribution to the literature. As to date, no “gold standard” wobble board assessment exists; such foundational knowledge provides the clinician with a new level of understanding, to justify and interpret clinical information. Wobble board performance should be compared to a single sex group, due to the differences between females and males. This study offers novel insights into the association between baseline characteristics and wobble board performance, which clinicians should integrate into their clinical reasoning. Habitual physical activity, as measured by a Baecke questionnaire, had no relationship with wobble board performance, therefore, advising an individual to increase physical activity is likely to have minimal impact on wobble board performance. Weight and upper body size did have a moderate relationship; hence, clinicians should acknowledge and accommodate the increased burden these specific factors may place on wobble board performance for an individual. Conducting wobble board assessments or rehabilitation with or without footwear, as the clinician sees fit, is recommended as it seems to make minimal difference overall. It is not possible to conclude whether an additional impact of dual tasking exists, since this is the first study to explore this notion and the findings were inconclusive.

4.5 Limitations

Since a young, healthy and unimpaired population conducted this study, caution is recommended when applying the findings to other populations. It is probable that learning effect or fatigue, due to repeated balance tasks, could have influenced the findings, however, the effect is likely to have been minimised, due to random task allocation.

5. Conclusion

This study provides the first systematic exploration of the effect of sex, footwear and dual tasking on wobble board performance and the finding are critical to aiding clinical decision making. The findings indicate that clinicians should compare wobble board performance to unisex cohorts, as females outperformed males, regardless of whether footwear or dual tasking was investigated. Modest correlations suggest clinicians should anticipate poorer wobble board performance in individuals who are heavier, with a larger upper body size or are taller. Wobble board performance, whilst wearing footwear, did not differ from that without footwear, therefore, clinicians should base footwear decisions on task specific rehabilitation goals. The effect of DT seemed to be task specific and further research is needed to understand the potential usefulness of an additional task.

Funding

The first author was funded by the Saudi Cultural Bureau in the United Kingdom, London and Princess Nourah Bint Abdulrahman University in Saudi Arabia, Riyadh.

Informed consent

Written informed consent was obtained from all participants prior to experimentation.

Ethical approval

The study follows the principles of the Declaration of Helsinki and was approved by the Princess Nourah bint Abdulrahman University Institutional Human Ethics Committee (H-01-R-059).

Author contributions

MA, MJ and JW have made substantial contributions to the conception, design of the study and final approval of the version to be submitted. MA and JW have considerably contributed to the acquisition, analysis and interpretation of data. MA, MJ and JW have drafted the article and revised it critically for important intellectual content.

Footnotes

Acknowledgments

The first author gratefully acknowledges Princess Nourah bint Abdulrahman University for funding her PhD program at Cardiff University. Also, thanks to Drs Ali Albarati, Abdulrahman Alsubiheen, Mazyad Alotaibi, Afrah Almuwais, Khaled AlGhamdi, Mrs Zahra Aseri and Mr.Abdulellah Alkhanfour for facilitating recruitment for this study.

Conflict of interest

The authors report no conflict of interest.

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Informing wobble-board training and assessment through an investigation of the effect of biological-sex,anthropometrics,footwear and dual-tasking in young adults

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

1.1 Biological sex and anthropometry

1.2 Footwear or no footwear

1.3 Primary and secondary tasking

2. Materials and methods

2.1 Design

2.2 Participants

2.3 Instrumentation

2.4 Procedure

Table 1 Results of wobble board performance as measured by stability index and statistical testing determining if biological sex affects wobble board performance with footwear (shod) and without footwear (unshod) conditions and during dual tasks (median and interquartile range)

2.6 Statistical analysis

3. Results

3.1 Biological sex

Table 2 Results of wobble board performance as measured by percentage time in each tilt banding and statistical testing determining if biological sex affects wobble board performance with footwear (shod) and without footwear (unshod) conditions and during dual tasks (median and interquartile range)

Table 4 Spearman’s rho ( r ) correlation between wobble board performance (tilt banding) and anthropometric characteristics

Table 6 Results of significance testing and effect size calculation for the effect of single and dual tasking on wobble board performance

4. Discussion

4.1 Biological sex

4.2 Anthropometry

4.3 Footwear vs without footwear

4.4 Single vs dual task

4.5 Limitations

5. Conclusion

Funding

Informed consent

Ethical approval

Author contributions

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Results of wobble board performance as measured by stability index and statistical testing determining if biological sex affects wobble board performance with footwear (shod) and without footwear (unshod) conditions and during dual tasks (median and interquartile range)

Table 2
Results of wobble board performance as measured by percentage time in each tilt banding and statistical testing determining if biological sex affects wobble board performance with footwear (shod) and without footwear (unshod) conditions and during dual tasks (median and interquartile range)

Table 4
Spearman’s rho ( $r$ ) correlation between wobble board performance (tilt banding) and anthropometric characteristics

Table 6
Results of significance testing and effect size calculation for the effect of single and dual tasking on wobble board performance