Rating of perceived difficulty scale for measuring intensity of standing balance exercises in individuals with vestibular disorders

Abstract

BACKGROUND:

A method for prescribing the difficulty or intensity of standing balance exercises has been validated in a healthy population, but requires additional validation in individuals with vestibular disorders.

OBJECTIVE:

This study validated the use of ratings of perceived difficulty for estimation of balance exercise intensity in individuals with vestibular disorders.

METHODS:

Eight participants with a confirmed diagnosis of a vestibular disorder and 16 healthy participants performed two sets of 16 randomized static standing exercises across varying levels of difficulty. Root Mean Square (RMS) of trunk angular velocity was recorded using an inertial measurement unit. In addition, participants rated the perceived difficulty of each exercise using a numerical scale ranging from 0 (very easy) to 10 (very difficult). To explore the concurrent validity of rating of perceived difficulty scale, the relationship between ratings of perceived difficulty and sway velocity was assessed using multiple linear regression for each group.

RESULTS:

The rating of perceived difficulty scale demonstrated moderate positive correlations RMS of trunk velocity in the pitch (r = 0.51, p < 0.001) and roll (r = 0.73, p < 0.001) directions in participants with vestibular disorders demonstrating acceptable concurrent validity.

CONCLUSIONS:

Ratings of perceived difficulty can be used to estimate the intensity of standing balance exercises in individuals with vestibular disorders.

Keywords

Rating of Perceived Difficulty dizziness postural control

1 Introduction

Balance is defined as the ability to maintain the upright position during static stance or dynamic activities such as walking or running. Maintenance of balance while performing various activities depends on the sensory information received from vision, from somatosensory feedback from joints and muscles, and from the vestibular apparatus [23, 32]. Balance disorders due to aging or disease within the central nervous system or peripheral balance organs may lead eventually to falling [4]. Vestibular hypofunction may contribute to increased body sway and risk of falling [2 , 50]. Approximately 65% of older people who fall have balance disorders [46] and among those, approximately 50% have vestibular disorders [38]. Two-thirds to three-quarters of older adults who have had fall-related hip or wrist fractures were found to have asymmetrical vestibular function [29, 30]. People with peripheral vestibular dysfunction may also restrict their activities and reduce their participation in daily life activities [17].

A recent Cochrane review and clinical practice guideline suggested there was moderate to strong evidence that vestibular rehabilitation is safe and effective in treating unilateral peripheral vestibular symptoms [19, 22]. In vestibular rehabilitation programs, a multitude of balance exercises can be prescribed by modifying the size of the base of support, altering the visual input, changing surface compliance, performing exercises in different postural positions such as sitting or standing, or generating different head movements [5, 28].

Despite the evidence for the benefit of vestibular rehabilitation in improving gaze stability and postural control in people with vestibular disorders [22, 24], there are few evidence-based guidelines for prescription or progression of the difficulty of balance exercises [10 , 39]. Difficulty is used as a synonym for well-known intensity parameter utilized in most other rehabilitation exercise prescription literature reports [39]. The magnitude of body sway is a commonly used proxy for difficulty of standing balance exercises [8]. Several instruments including force plates and accelerometers have been used to measure body sway [6 , 51]. However, force plates are not portable and are relatively expensive for rehabilitation clinics. Accelerometers incorporated into personal mobile devices are becoming more popular as activity monitors. Despite their portability, widespread use of accelerometers for measuring postural sway in the clinic has not yet been adopted, most likely due to barriers related to time of set-up and analysis. Therefore, a more convenient yet valid way to measure intensity of balance exercises in a wide range of clinical settings is needed. Recently, Alsubaie et al. developed a rating of perceived difficulty (RPD) scale from 0 to 10 for estimating intensity of standing balance exercises, which is similar to rating of perceived exertion scales validated for estimating intensity of aerobic and resistance exercises [7]. The RPD scale was validated in healthy participants by correlating the RPD measure with magnitude of body sway and velocity using an inertial measurement unit [7]. However, the scale has not been validated in persons with vestibular disorders.

The primary purpose of this study was to validate ratings of perceived difficulty against postural sway responses in people with vestibular disorders. Validation of the ratings of perceived difficulty will allow clinicians to better prescribe and progress standing balance exercises in much the same way that ratings of perceived exertion are used for aerobic exercises. In addition, the magnitude of ratings in people with vestibular disorders was compared with healthy age-matched controls across similar exercises in order to determine if individuals with vestibular disorders had a greater sense of difficulty per unit of sway compared with controls. We hypothesized that participants with vestibular disorders would have greater ratings of perceived difficulty during the performance of standing balance exercises compared with healthy age-matched controls.

2 Methods

2.1 Participants

Eight participants with vestibular disorders were recruited from the Balance Disorders Clinic of the University of Pittsburgh Medical Center. A confirmed diagnosis of peripheral or central vestibular disorder was made by a neurotologist based on history, caloric testing, rotational chair testing, and vestibular evoked myogenic potential testing. Participants with vestibular disorders were gender and age (±3 years of age) matched with 16 healthy participants in a ratio of 1:2. The matched healthy participants’ data were used from the parent study [7, 8].

Participants with vestibular disorders and healthy participants were between the ages of 18 and 85 years old and participating in daily activities independently. Participants were excluded if they were unable to stand for 3 minutes without rest; had distal sensory loss (unable to complete the Romberg test for 30 seconds and unable to feel a pressure of 4.31 g monofilament applied on two different parts of each foot with eyes closed); had corrected visual acuity worse than 20/40, had a diagnosis of benign paroxysmal positional vertigo (BPPV) (positive Dix–Hallpike test or positive Roll test); had a history of neurological or orthopedic disorders; used an assistive device for ambulation; were pregnant; had excessive weight (BMI >35); or had cognitive impairment (≤25 points on the Montreal Cognitive Assessment). Additionally, healthy participants were excluded if they had a history of falling two times or more within the last 12 months doing activities of daily living; or had a peripheral vestibular disorder based on a positive head impulse test.

This study was approved by the Institutional Review Board of the University of Pittsburgh. All participants signed an informed consent form prior to participating in the study.

2.2 Experimental procedure

Eligible participants who met the study criteria completed the Activities-specific Balance Confidence Scale (ABC) questionnaire [41], Functional Gait Assessment (FGA) [54], and gait speed measured over the course of 6.1 meters [44] prior to the experiment to better describe the participants. Moreover, participants with vestibular disorders completed the Dizziness Handicap Inventory (DHI) [27] and the self-report of dizziness on a 0–10 verbal scale [18, 47].

2.3 Experimental visit

During the experimental visit, participants with vestibular disorders and matched healthy participants were asked to perform two sets of 16 randomized static standing balance exercises, which were a full-factorial design of the following different conditions: vision (eyes open and eyes closed); surface (firm and foam); base of support (feet apart and semi-tandem); head movement (head still and yaw) (Table 1). Please refer to Alsubaie et al. for a complete description of the conditions [7, 8]. Participants were instructed to stand as stable as possible with bare feet and arms at their side for 35 seconds each trial.

Table 1
Balance exercises

Exercise number Surface Visual input Base of support Head movement

1 Firm Eyes open Feet apart Head still

2 Firm Eyes open Feet apart Yaw

3 Firm Eyes open Semi-tandem Head still

4 Firm Eyes open Semi-tandem Yaw

5 Firm Eyes closed Feet apart Head still

6 Firm Eyes closed Feet apart Yaw

7 Firm Eyes closed Semi-tandem Head still

8 Firm Eyes closed Semi-tandem Yaw

9 Foam Eyes open Feet apart Head still

10 Foam Eyes open Feet apart Yaw

11 Foam Eyes open Semi-tandem Head still

12 Foam Eyes open Semi-tandem Yaw

13 Foam Eyes closed Feet apart Head still

14 Foam Eyes closed Feet apart Yaw

15 Foam Eyes closed Semi-tandem Head still

16 Foam Eyes closed Semi-tandem Yaw

Exercise number	Surface	Visual input	Base of support	Head movement
1	Firm	Eyes open	Feet apart	Head still
2	Firm	Eyes open	Feet apart	Yaw
3	Firm	Eyes open	Semi-tandem	Head still
4	Firm	Eyes open	Semi-tandem	Yaw
5	Firm	Eyes closed	Feet apart	Head still
6	Firm	Eyes closed	Feet apart	Yaw
7	Firm	Eyes closed	Semi-tandem	Head still
8	Firm	Eyes closed	Semi-tandem	Yaw
9	Foam	Eyes open	Feet apart	Head still
10	Foam	Eyes open	Feet apart	Yaw
11	Foam	Eyes open	Semi-tandem	Head still
12	Foam	Eyes open	Semi-tandem	Yaw
13	Foam	Eyes closed	Feet apart	Head still
14	Foam	Eyes closed	Feet apart	Yaw
15	Foam	Eyes closed	Semi-tandem	Head still
16	Foam	Eyes closed	Semi-tandem	Yaw

Data collection was stopped if a participant lost their balance according to the following failure criteria: stepped out of position, changed their feet or arms starting position, and/or touched something for support. Participants were asked to repeat failed trials once in each set if they lost their balance before completing the 35 second trial. Participants were guarded by a physical therapist during all exercises and wore a safety harness to prevent a fall. There was a seated rest break of 1 minute after every three exercises to avoid fatigue.

2.4 Outcome measures

2.4.1 Sway measures

An inertial measurement unit (IMU, Xsense Technologies B.V., Enschede, The Netherlands) was mounted on each participant’s lower back at the level of iliac crest (L4) to record trunk angular velocity in the pitch and roll directions at a sampling rate of 100 Hz.

Sway velocity was recorded during all trials for 35 seconds and the first 5 seconds of data collection were removed to avoid the effect of the participant’s initial establishment of balance [37, 43]. Summary measures of sway velocity were calculated from the remainder of the time series. The data were low-pass filtered using a second order Butterworth filter with a cut-off frequency of 3 Hz [13, 14]. During the analysis, each trial was plotted individually and inspected visually using MATLAB software to make sure that there were no extraneous movements.

The Root-Mean-Square (RMS) of the trunk angular velocity in the pitch and roll directions was calculated and used in the analysis to test the hypotheses. The RMS was calculated as follows:

$RMS = \sqrt[2]{\frac{\sum_{i = o}^{n} (a_{i}^{2})}{n}}$ (1) where a is instantaneous sway value with mean value subtracted where “i” is an individual data sample and “n” is the total number of samples.

2.4.2 Rating of Perceived Difficulty (RPD)

Participants rated their perceived difficulty of each exercise using a rating scale developed by Alsubaie et al. that ranges from 0 to 10, where 0 indicates that the exercise is extremely easy whereas 10 indicates that the exercise is extremely hard (Fig. 1) [7]. During the experiment, the rating scale was placed on the sidewall so that participants could look at it after each exercise.

Fig. 1

Rating of perceived difficulty scale [7].

2.5 Statistical analyses

Participants’ demographic characteristics were compared between groups using independent samples t-test for dependent variables that were continuous and normally distributed. The Mann-Whitney U test was used to compare differences between the two independent groups when dependent variables were continuous but not normally distributed.

2.5.1 Validation of ratings of perceived difficulty

To assess the concurrent validity of the RPD scale, the relationship between RPD and RMS of trunk angular velocity was assessed using the multiple regression method [11]. The RPD was the outcome variable and the participants and postural measures were the predictor variables. From the regression analysis of variance table, the amount of variation in RPD due to variation in postural measure magnitude, while controlling for the inter-subject variability, was computed by the following formula: Correlation = sqrt (SS_{posturalmeasure} / SS_{posturalmeasure} + SS_residual), where SS is the sum of squares. The direction of the correlation is given by the sign of the slope of the regression coefficient between the rating of perceived difficulty and postural measure. The average value of the two trials of the dependent variables was used in the analysis. This analysis was performed separately for individuals with vestibular disorders and healthy controls. Additionally, the slope of the relationship between the RPD and RMS of the sway velocity was computed for each participant using linear regression to examine the variability within and between groups.

2.5.2 Postural sway

A Linear Mixed Model (LMM) was used to determine the main effect of group and its interaction with the factors of vision, surface, base of support and head movement on the RMS sway velocity in the pitch and roll directions. Due to the presence of missing data in this study, the decision was made to use LMM as it allowed us to evaluate the effects with the presence of missing data. Additionally, LMM allowed inclusion of participants as a random effect, and assumed that each participant had his/her own intercept value. The average value of the two trials of the dependent variables was used because it was determined that there was no difference between trials. Due to the high incompletion rate of exercise 16, especially for people with vestibular disorders, it was eliminated from the linear mixed model analysis. The significance level was α= 0.05.

2.5.3 Ratings of perceived difficulty

For the RPD data that were ordinal, the Mann-Whitney U test was used to compare differences in RPD between the two groups and the factors of vision, surface, base of support and head movement. The mean value of the two trials of the RPD was used. The effect of the balance conditions was tested using the Wilcoxon Signed Ranks test.

3 Results

3.1 Descriptive statistics

Eight participants with vestibular disorders met all the eligibility criteria (Table 2). The eligible participants had a mean age of 56±16 years (four females). The 16 age-matched healthy participants were recruited from a larger study and had a mean age of 56±16 years. The participants with vestibular disorders had normal gait speed [1 , 33]. Age and gait speed differences between participants with vestibular disorders and controls were not statistically significant (t(22) = 0.009, p = 0.99) and (t(22) = 0.53, p = 0.59) respectively. Similarly, differences between participants with vestibular disorders and controls were not statistically significant on scores of the Activities-specific Balance Confidence (ABC) Scale and Functional Gait Assessment (FGA).

Table 2
Characteristics of participants with vestibular disorders and controls

Characteristics Vestibular Disorders Controls

n = 8 n = 16

Age, y, Mean±SD 56±16 56±16

Gender, female, n (%) 4 (50) 8 (50)

Body Mass Index, kg/m², Median (Range) 24.78 (19–30) 26.50 (15–35)

Monofilament, Median (Range) 4.08 (3.61–4.17) 3.84 (3.22–4.17)

Montreal Cognitive Assessment, Median (Range) 28.5 (26–30) 29 (26–30)

Activities-specific Balance Confidence, Median (Range) 93 (59–98) 95 (81–100)

Gait Speed, m/s, Mean (SD) 1.31 (0.27) 1.35 (0.18)

Functional Gait Assessment, Median (Range) 26 (22–30) 28 (19–30)

Dizziness Handicap Inventory, Median (Range) 23 (0–50) N/A

Dizziness Visual Analog Scale, Mean (SD) 0.84 (1.16) N/A

Characteristics	Vestibular Disorders	Controls
Age, y, Mean±SD	56±16	56±16
Gender, female, n (%)	4 (50)	8 (50)
Body Mass Index, kg/m², Median (Range)	24.78 (19–30)	26.50 (15–35)
Monofilament, Median (Range)	4.08 (3.61–4.17)	3.84 (3.22–4.17)
Montreal Cognitive Assessment, Median (Range)	28.5 (26–30)	29 (26–30)
Activities-specific Balance Confidence, Median (Range)	93 (59–98)	95 (81–100)
Gait Speed, m/s, Mean (SD)	1.31 (0.27)	1.35 (0.18)
Functional Gait Assessment, Median (Range)	26 (22–30)	28 (19–30)
Dizziness Handicap Inventory, Median (Range)	23 (0–50)	N/A
Dizziness Visual Analog Scale, Mean (SD)	0.84 (1.16)	N/A

Individual diagnoses and vestibular function test abnormalities are detailed in Table 3. Seven of the eight participants had a clinically significant peripheral abnormality. Seven participants had a directional preponderance on rotational chair test, five had a caloric asymmetry, four had VEMP dysfunction, and four had static positional nystagmus. Regarding individuals with vestibular disorders’ scores on the Activities-specific Balance Confidence (ABC) Scale, five participants were within a high level of physical functioning and three had a moderate level of functionality with a score less than 80 [26 , 41]. Four participants with vestibular disorders were within 95% confidence limits of age-normed performance on the FGA and four were below normal [49, 53]. Six participants with vestibular disorders were mildly affected by dizziness (0–30 DHI) and two were affected moderately by their dizziness (31–60 DHI) [52]. Four participants with vestibular disorders indicated mild perceived level of dizziness on a visual analog scale before starting the experiment and the other four participants were normal.

Table 3

Demographic and clinical characteristics of individual participants with vestibular disorders

Participant	Sex	Age (years)	Diagnosis	Abnormal Vestibular Function Test	ABC	Gait Speed (m/s)	FGA	DHI	Dizziness (VAS)
1	Female	74	Sequelae of a left peripheral vestibulopathy	•VEMP: Bilateral	97	0.91	26	0	0
•Caloric: Left 52% RVR
2	Female	69	Ménière’s disease	•VEMP: Right	59*	1.42	24*	50*	3.1*
•Static positional: nystagmus >5 deg/s in 4 positions
•Rotational chair: Mild Left DP
3	Male	35	Left peripheral vestibulopathy	•Static positional: nystagmus = 6 deg/s in supine position	94	1.30	26*	20	0.6*
•Caloric: Left 100% RVR
•Rotational chair: Mild Right DP
4	Male	40	Left peripheral vestibulopathy	•VEMP: Left	98	1.54	30	28	0
•Rotational chair: Mild Right DP
5	Male	36	Left peripheral vestibulopathy	•Caloric: Left 100% RVR	96	1.29	30	42*	1.9*
•Rotational chair: Mild Left DP
6	Female	60	Right peripheral vestibulopathy	•Caloric: Right 100% RVR	69*	1.31	22*	24	0
•Rotational chair: Mild Right DP
7	Male	66	Dizziness of uncertain etiology ongoing	•Static positional: nystagmus = 6 deg/s in right lateral position	92	1.72	29	8	1.1*
vestibular ocular reflex asymmetry	•Rotational chair: Mild Right DP
8	Female	67	Right peripheral vestibulopathy	•VEMP: Right	74*	0.95	22*	14	0
			•Static positional: nystagmus = 8 deg/s in head left position
			•Caloric: Right 75% RVR
			•Rotational chair: Mild Left DP

VEMP: vestibular-evoked myogenic potentials; deg: degree; s: second; RVR: reduced of vestibular response; DP: Directional Preponderance; ABC: Activities-specific Balance Confidence; FGA: Functional Gait Assessment; DHI: Dizziness Handicap Inventory; VAS: Visual Analog Scale; *: indicates scores outside of range considered within normal limits.

3.2 Validation of ratings of perceived difficulty

Multiple regression analysis results demonstrated that there were moderate positive correlations between the RPD and RMS of trunk velocity in the pitch (r = 0.51, p < 0.001, power = 0.44) and roll (r = 0.73, p < 0.001, power = 0.84) directions in individuals with vestibular disorders group. Furthermore, there were moderate to strong positive correlations in the healthy control group between the RPD and RMS of trunk angular velocity in the pitch (r = 0.76, p < 0.001, power = 0.99) and roll (r = 0.69, p < 0.001, power = 0.98) directions. A test to see if the correlation coefficients differed between groups was not significant for pitch (z = 0.82, p = 0.21) or roll velocity (z = 0.15, p = 0.44) [31].

The relationships between mean values of RPD and mean values of pitch and roll velocity for individuals with vestibular disorders and controls are illustrated in Figs. 2 and 3. Each data point represents an individual balance condition. The full range of the RPD is used by both groups. It is evident that the sway velocity values have a greater range for the vestibular disorders group compared with the control group, resulting in a smaller change in RPD relative to change in sway velocity for the participants with vestibular disorders. Participant-specific slopes were determined using linear regression. For the relationship with pitch velocity, the mean slope for people with vestibular disorders was 1.1 (SD 0.7) compared with a slope of 3.3 (SD 1.2) for controls (p < 0.001). For roll velocity, the vestibular disorders group had a slope of 1.0 (SD 0.6), compared with a slope of 2.5 (SD 1.2) for controls (p < 0.001).

Fig. 2

Relationship between average of ratings of perceived difficulty and average of the RMS of pitch angular velocity in controls and individuals with vestibular disorders with line of best fit. Each of the 16 balance conditions is represented by one data point.

Fig. 3

Relationship between average of ratings of perceived difficulty and average of the root-mean-square (RMS) of roll angular velocity in controls and individuals with vestibular disorders with line of best fit. Each of the 16 balance conditions is represented by one data point.

3.3 Postural sway

Results of the linear mixed model showed that the sway velocity measures were significantly higher in individuals with vestibular disorders compared to healthy controls in the pitch (VEST: 2.3±1.8 deg/s and CON: 1.0±0.7 deg/s, p = 0.048) and roll (VEST: 3.6±2.7 and CON: 1.0.±0.9, p < 0.001) directions. The main effects of vision, surface, base of support, and head movement were statistically significant (p < 0.001, Table 4). The closed-eyes, foam surface, semi-tandem stance, yaw head movement conditions produced significantly higher sway than the open-eyes, firm surface, feet apart stance, head still conditions respectively in all sway measures. There was a significant (p < 0.001) group by surface interaction for pitch and roll sway. In addition, there were significant (p < 0.01) group by vision, group by base of support, and group by head movement interactions for roll sway only. The significant interactions indicated that for each condition, the amount of change was greater for the vestibular disorders group compared with the control group.

Table 4
Mean (SD) of the Root-Mean-Square (RMS) Pitch and Roll Velocity for the experimental main effects. P-values for the main effects

RMS Pitch Velocity (deg/s) RMS Roll Velocity (deg/s)

Vestibular Disorders Controls p Vestibular Disorders Controls p

Surface: Firm 1.6 (0.9) 0.7 (0.4) <0.001 2.8 (2.0) 0.7 (0.6) <0.001

Surface: Foam 3.1 (2.3) 1.3 (0.8) 4.6 (3.1) 1.2 (1.1)

Vision: Eyes Open 2.1 (1.9) 0.9 (0.7) <0.001 3.2 (2.3) 0.9 (0.8) <0.001

Vision: Eyes Closed 2.5 (1.8) 1.1 (0.7) 4.0 (3.1) 1.1 (1.0)

Base: Feet Apart 2.1 (1.9) 0.8 (0.5) <0.001 2.7 (2.0) 0.7 (0.6) <0.001

Base: Semi-tandem 2.6 (1.8) 1.2 (0.7) 4.5 (3.1) 1.3 (1.0)

Head: Still 2.1 (1.5) 0.7 (0.5) <0.001 3.0 (2.7) 0.5 (0.5) <0.001

Head: Yaw 2.6 (2.1) 1.3 (0.7) 4.3 (2.7) 1.4 (1.0)

	RMS Pitch Velocity (deg/s)	RMS Roll Velocity (deg/s)
Surface: Firm	1.6 (0.9)	0.7 (0.4)	<0.001	2.8 (2.0)	0.7 (0.6)	<0.001
Surface: Foam	3.1 (2.3)	1.3 (0.8)		4.6 (3.1)	1.2 (1.1)
Vision: Eyes Open	2.1 (1.9)	0.9 (0.7)	<0.001	3.2 (2.3)	0.9 (0.8)	<0.001
Vision: Eyes Closed	2.5 (1.8)	1.1 (0.7)		4.0 (3.1)	1.1 (1.0)
Base: Feet Apart	2.1 (1.9)	0.8 (0.5)	<0.001	2.7 (2.0)	0.7 (0.6)	<0.001
Base: Semi-tandem	2.6 (1.8)	1.2 (0.7)		4.5 (3.1)	1.3 (1.0)
Head: Still	2.1 (1.5)	0.7 (0.5)	<0.001	3.0 (2.7)	0.5 (0.5)	<0.001
Head: Yaw	2.6 (2.1)	1.3 (0.7)		4.3 (2.7)	1.4 (1.0)

3.4 Ratings of perceived difficulty

The results of the Mann-Whitney U test did not demonstrate a significant difference in mean RPD between individuals with vestibular disorders (3.8±1.1) and controls (3.0±1.1) (U = 90.5, p = 0.11). Across both groups, the mean RPD was greater on the foam surface compared with firm, greater with eyes closed compared with eyes opened, greater with semi-tandem base of support compared with feet-apart, and greater with head moving in the yaw plane compared with being still (Table 5).

Table 5
Mean (SD) of the Rating of Perceived Difficulty for the experimental main effects

Exercise Conditions Rating of Perceived Difficulty Mean (SD) Wilcoxon Signed Ranks

Surface: Firm 2.1 (2.1) Z = 4.2, p < 0.001

Surface: Foam 4.5 (2.9)

Vision: Eyes Open 2.8 (2.4) Z = 3.7, p < 0.001

Vision: Eyes Closed 3.8 (3.0)

Base: Feet Apart 1.7 (1.7) Z = 4.3, p < 0.001

Base: Semi-tandem 4.9 (2.8)

Head: Still 2.5 (2,1) Z = 4.2, p < 0.001

Head: Yaw 4.1 (3.1)

Exercise Conditions	Rating of Perceived Difficulty Mean (SD)	Wilcoxon Signed Ranks
Surface: Firm	2.1 (2.1)	Z = 4.2, p < 0.001
Surface: Foam	4.5 (2.9)
Vision: Eyes Open	2.8 (2.4)	Z = 3.7, p < 0.001
Vision: Eyes Closed	3.8 (3.0)
Base: Feet Apart	1.7 (1.7)	Z = 4.3, p < 0.001
Base: Semi-tandem	4.9 (2.8)
Head: Still	2.5 (2,1)	Z = 4.2, p < 0.001
Head: Yaw	4.1 (3.1)

Wilcoxon Signed Ranks test for the effect of the different levels for each exercise condition (e.g. firm v. foam surface).

Fig. 4

Mean root-mean-square (RMS) of pitch velocity (graph A) or roll velocity (graphs B-E) for individuals with vestibular disorders and controls, demonstrating significant interaction between participant group and exercise condition. (A) pitch velocity, group*surface interaction; (B - E) roll velocity, group*surface, group*vision, group*stance, and group*head movement. Error Bars represent 1 standard deviation.

4 Discussion

The primary purpose of this study was to validate ratings of perceived difficulty with postural sway responses in people with vestibular disorders. We discovered a significant linear association between RPD scores and postural sway in the individuals with vestibular disorders, similar to the finding in age-matched healthy controls in this study and previous work [7]. The association between RPD and sway velocity was considerably stronger in the roll direction compared with the pitch direction for the vestibular disorders group, which replicated the finding in the full control sample [7], suggesting perhaps that the RPD rating was based more on perception of medio-lateral (ML) stability versus antero-posterior (AP) stability in the vestibular disorders group.

Contrary to our initial expectation that individuals with vestibular disorders would have a greater change in rating of perceived difficulty relative to change in unit of sway velocity (i.e., slope), the vestibular disorders group had a smaller slope than healthy controls. The primary reason driving this difference was that individuals with vestibular disorders had significantly greater sway than controls, while both groups used the full range of the RPD scale. One interpretation of this finding is that individuals normalize their RPD based on the amount of body sway that they are accustomed to generating. We also discovered considerable variability in the slope within each group. Both observations lend credence to the concept of using RPD as an individualized measure of intensity of balance difficulty, rather than using a purely quantitative or visual estimation of body sway. This is consistent with the use of ratings of perceived exertion for aerobic exercise activities in people with chronic disease.

The participants with vestibular disorders had peripheral dysfunction in seven of eight cases. On average, they demonstrated a good level of function, similar to what has been reported by other studies about general populations of community-dwelling adults’ gait speed [1 , 48], Functional Gait Assessment (FGA) [49, 53], and Activities-specific Balance Confidence (ABC) scale scores [26, 36]. Compared to healthy controls who were included in this study and were age and gender matched, people with vestibular disorders had similar gait speed, FGA, and ABC scores. Compared with other studies, individuals with vestibular disorders in this study had similar average gait speed to what has been reported by Hall and Herdman [18], higher median FGA scores compared with what Wrisley et al. reported [54], and a higher (better) median ABC score than what was reported in Marchetti et al.’s study of 95 people with signs and symptoms of vestibular dysfunction [34].

Vestibular disorders have been reported to contribute to increasing postural instability [9, 16]. In agreement with results of previous studies, the results of this study showed that participants with vestibular disorders had higher postural sway compared to healthy matched participants on all postural sway measures. The findings of our study are consistent with the work of Baloh et al. that used relatively similar exercise conditions and found a difference in postural sway measurements between two groups of elderly people of similar age, one of whom suffers from imbalance [9].

The difference between participants with vestibular disorders and healthy participants for the roll sway measure was more pronounced and more than double the sway in the pitch direction. This increase in the amount of sway in the lateral direction may be due to the conditions with semi-tandem stance, which may have required participants, especially those with balance problems, to sway more in the lateral direction. This large variation in the amount of sway in the lateral direction may explain the higher reliability of the amount of sway in this direction compared to the AP direction, which was reported in a number of previous studies [8 , 45].

Although people with vestibular disorders rated the difficulty of exercises nearly one point higher than control participants on average, the rating of perceived difficulty scores were not significantly different between participants with vestibular disorders and control participants. The discrepancy between the sway measures demonstrating differences between the groups, and the ratings of perceived difficulty, may indicate that individuals with vestibular disorders may not perceive the increase in sway as a difficulty to their balance control, and this may be due to their higher functional abilities compared to patients in other studies. Furthermore, the small sample size of people with vestibular disorders may have decreased the power of finding a statistically significant difference between participants with vestibular disorders and healthy matched participants in the ratings of perceived difficulty.

One limitation of the study was the relatively small sample of people with vestibular disorders, which may limit the generalizability of study results. In particular, seven of the eight participants had a peripheral abnormality, and it is not clear in individuals with central vestibular dysfunction or BPPV would produce similar results. Furthermore, the duration of the condition may impact participants reporting of difficulty, and this data was not obtained. However, the results of the validation were clear and consistent with the full health cohort study [7]. Second, the duration of the experimental visit in this study lasted about an hour and a half, which may have caused fatigue, especially for those with vestibular disorders. However, the participants in this study performed the exercises in a random order in each set to avoid the order effect resulting from fatigue.

In conclusion, the results of this study showed moderate positive correlations between RPD and postural sway measures, which means that the RPD scale can be used to estimate the intensity of standing balance exercises in individuals with unilateral hypofunction and possibly individuals with other vestibular disorders. We believe that this finding will lead to several important clinical uses for the RPD scale. First, the clinician will be able to reliably quantify the intensity of balance exercises across the diverse range of exercises that can be prescribed. A database of relative difficulty of exercises could be produced to aid clinicians, similar to databases summarizing the aerobic energy cost of exercise activities [3]. Second, by having a quantitative measure, the intensity can be documented and prescribed so that the patient is achieving a certain level of difficulty. A key to improving performance is to challenge the system, and the RPD provides a metric of this challenge. Third, a clinician could document the RPD during performance of a standard exercise over time, and thus indicate improvement if the RPD was lower at discharge compared with the first time that they performed the balance exercise. Future investigation of the RPD scale is warranted. Additionally, it would be important to generalize these findings to individuals with other types of vestibular disorders including BPPV and central vestibular dysfunction, and to validate the RPD for other exercise tasks including during gait, transitional balance movements, gaze stabilization and visual habituation exercises.

Footnotes

Acknowledgments

The research was partially funded by the National Institutes of Health through Grants UL1TR001857 (University of Pittsburgh CTSI) and R21-DC012410 (SLW and KHS). This publication was supported by the Deanship of Scientific Research at Prince Sattam bin Abdulaziz University, Alkharj, Saudi Arabia.

We would like to acknowledge the University of Pittsburgh Clinical and Translational Science Institute (CTSI) for helping with participant recruitment. We would like to acknowledge the assistance of the following people in helping with data collection: Dr. Abdulaziz Alkathiry, Anita Lieb, Susan Strelinski, Dr. Chia-Cheng Lin, Dr. Mohammed Alyabroudi, Dr. Bader Alqahtani, Dr. Sahar Abdulaziz, Dr. Kefah Alshebber, Dr. Brooke Klatt, Dr. Carrie Hoppes, David Fear, and Mohammed Almotairi.

Conflicts of interest disclosure

None.

References

Abellan van Kan

, Rolland

, Andrieu

, Bauer

, Beauchet

, Bonnefoy

, Cesari

, Donini

L.M.

, Gillette Guyonnet

, Inzitari

, Nourhashemi

, Onder

, Ritz

, Salva

, Visser

, Vellas

, Gait speed at usual pace as a predictor of adverse outcomes in community-dwelling older people an International Academy on Nutrition and Aging (IANA) Task Force, J Nutr Health Aging 13 (2009), 881–889.

Agrawal

, Carey

J.P.

, Della Santina

C.C.

, Schubert

M.C.

, Minor

L.B.

Disorders of balance and vestibular function in US adults: Data from the National Health and Nutrition Examination Survey, Arch Intern Med 169 (2009), 938–944.

Ainsworth

B.E.

, Haskell

W.L.

, Herrmann

S.D.

, Meckes

, Bassett

D.R.

, Tudor-Locke

, Greer

J.L.

, Vezina

, Whitt-Glover

M.C.

, Leon

A.S.

Compendium of Physical Activities: A second update of codes and MET values, Med Sci Sports Exerc 43 (2011), 1575–1581.

Alexander

N.B.

Postural control in older adults, J Am Geriatr Soc 42 (1994), 93–108.

Alsalaheen

B.A.

, Whitney

S.L.

, Mucha

, Morris

L.O.

, Furman

J.M.

, Sparto

P.J.

Exercise prescription patterns in patients treated with vestibular rehabilitation after concussion, Physiotherapy Research International 18 (2013), 100–108.

Alsubaie

S.F.

The postural stability measures most related to aging, physical performance, and cognitive function in healthy adults, Biomed Res Int 2020 (2020), 5301534.

Alsubaie

S.F.

, Whitney

S.L.

, Furman

J.M.

, Marchetti

G.F.

, Sienko

K.H.

, Klatt

B.N.

, Sparto

P.J.

Reliability and validity of ratings of perceived difficulty during performance of static standing balance exercises, Phys Ther (2019).

Alsubaie

S.F.

, Whitney

S.L.

, Furman

J.M.

, Marchetti

G.F.

, Sienko

K.H.

, Sparto

P.J.

Reliability of postural sway measures of standing balance tasks, J Appl Biomech (2018), 1–23.

Baloh

R.W.

, Jacobson

K.M.

, Enrietto

J.A.

, Corona

, Honrubia

Balance disorders in older persons: Quantification with posturography, Otolaryngol Head Neck Surg 119 (1998), 89–92.

10.

Bao

, Klatt

B.N.

, Whitney

S.L.

, Sienko

K.H.

, Wiens

Automatically evaluating balance: A machine learning approach, IEEE Trans Neural Syst Rehabil Eng 27 (2019), 179–186.

11.

Bland

J.M.

, Altman

D.G.

Calculating correlation coefficients with repeated observations: Part 2–Correlation between subjects, BMJ 310 (1995), 633.

12.

Bohannon

R.W.

Comfortable and maximum walking speed of adults aged 20-79 years: Reference values and determinants, Age Ageing 26 (1997), 15–19.

13.

Dozza

, Chiari

, Horak

F.B.

Audio-biofeedback improves balance in patients with bilateral vestibular loss, Arch Phys Med Rehabil 86 (2005), 1401–1403.

14.

Dozza

, Horak

F.B.

, Chiari

Auditory biofeedback substitutes for loss of sensory information in maintaining stance, Exp Brain Res 178 (2007), 37–48.

15.

Farlie

M.K.

, Robins

, Keating

J.L.

, Molloy

, Haines

T.P.

Intensity of challenge to the balance system is not reported in the prescription of balance exercises in randomised trials: A systematic review, J Physiother 59 (2013), 227–235.

16.

Fujimoto

, Egami

, Kinoshita

, Sugasawa

, Yamasoba

, Iwasaki

Postural stability in vestibular neuritis: Age, disease duration, and residual vestibular function, Laryngoscope 124 (2014), 974–979.

17.

Giray

, Kirazli

, Karapolat

, Celebisoy

, Bilgen

, Kirazli

Short-term effects of vestibular rehabilitation in patients with chronic unilateral vestibular dysfunction: A randomized controlled study, Arch Phys Med Rehabil 90 (2009), 1325–1331.

18.

Hall

C.D.

, Herdman

S.J.

Reliability of clinical measures used to assess patients with peripheral vestibular disorders, J Neurol Phys Ther 30 (2006), 74–81.

19.

Hall

C.D.

, Herdman

S.J.

, Whitney

S.L.

, Cass

S.P.

, Clendaniel

R.A.

, Fife

T.D.

, Furman

J.M.

, Getchius

T.S.

, Goebel

J.A.

, Shepard

N.T.

, Woodhouse

S.N.

Vestibular rehabilitation for peripheral vestibularhypofunction: An evidence-based clinical practice guideline: Fromthe American physical therapy association neurology section, Journal of Neurologic Physical Therapy 40 (2016), 124–155.

20.

Heebner

N.R.

, Akins

J.S.

, Lephart

S.M.

, Sell

T.C.

Reliability and validity of an accelerometry based measure of static and dynamic postural stability in healthy and active individuals, Gait Posture 41 (2015), 535–539.

21.

Herdman

S.J.

, Blatt

, Schubert

M.C.

, Tusa

R.J.

Falls in patients with vestibular deficits, Am J Otol 21 (2000), 847–851.

22.

Hillier

S.L.

, McDonnell

Vestibular rehabilitation for unilateral peripheral vestibular dysfunction, Cochrane Database Syst Rev (2011), CD005397.

23.

Horak

F.B.

Postural orientation and equilibrium: What do we need to know about neural control of balance to prevent falls?

Age Ageing 35(Suppl 2) (2006), ii7–ii11.

24.

Horak

F.B.

, Jones-Rycewicz

, Black

F.O.

, Shumway-Cook

Effects of vestibular rehabilitation on dizziness and imbalance, Otolaryngol Head Neck Surg 106 (1992), 175–180.

25.

Hornyak

, VanSwearingen

J.M.

, Brach

J.S.

Measurement of gait speed, Topics in Geriatric Rehabilitation 28 (2012), 6.

26.

Huang

T.T.

, Wang

W.S.

Comparison of three established measures of fear of falling in community-dwelling older adults: Psychometric testing, Int J Nurs Stud 46 (2009), 1313–1319.

27.

Jacobson

G.P.

, Newman

C.W.

The development of the Dizziness Handicap Inventory, Arch Otolaryngol Head Neck Surg 116 (1990), 424–427.

28.

Klatt

B.N.

, Carender

W.J.

, Lin

C.C.

, Alsubaie

S.F.

, Kinnaird

C.R.

, Sienko

K.H.

, Whitney

S.L.

A conceptual framework for the progression of balance exercises in persons with balance and vestibular disorders, Phys Med Rehabil Int 2 (2015).

29.

Kristinsdottir

E.K.

, Jarnlo

G.B.

, Magnusson

Asymmetric vestibular function in the elderly might be a significant contributor to hip fractures, Scand J Rehabil Med 32 (2000), 56–60.

30.

Kristinsdottir

E.K.

, Nordell

, Jarnlo

G.B.

, Tjader

, Thorngren

K.G.

, Magnusson

Observation of vestibular asymmetry in a majority of patients over 50 years with fall-related wrist fractures, Acta Otolaryngol 121 (2001), 481–485.

31.

Lenhard

, Lenhard

Hypothesis Tests for Comparing Correlations, Psychometrica, Bibergau, Germany, 2014.

32.

Lord

S.R.

, Clark

R.D.

, Webster

I.W.

Postural stability and associated physiological factors in a population of aged persons, J Gerontol 46 (1991), M69–M76.

33.

Lusardi

M.M.

, Marjorie

G.L.

, Schulman

Functional performance in community living older adults, J Geriatr Phys Ther 26 (2003), 9.

34.

Marchetti

G.F.

, Whitney

S.L.

, Redfern

M.S.

, Furman

J.M.

Factors associated with balance confidence in older adults with health conditions affecting the balance and vestibular system, Arch Phys Med Rehabil 92 (2011), 1884–1891.

35.

Michelle

G.L.P.

, Lusardi

Marjorie schulman, functional performance in community living older adults, J Geriatr Phys Ther 26 (2003), 9.

36.

Myers

A.M.

, Fletcher

P.C.

, Myers

A.H.

, Sherk

Discriminative and evaluative properties of the activities-specific balance confidence (ABC) scale, J Gerontol A Biol Sci Med Sci 53 (1998), M287–M294.

37.

O’Sullivan

, Blake

, Cunningham

, Boyle

, Finucane

Correlation of accelerometry with clinical balance tests in older fallers and non-fallers, Age Ageing 38 (2009), 308–313.

38.

Overstall

P.W.

, Exton-Smith

A.N.

, Imms

F.J.

, Johnson

A.L.

Falls in the elderly related to postural imbalance, Br Med J 1 (1977), 261–264.

39.

L.S. Pescatello and American College of Sports Medicine, ACSM’s guidelines for exercise testing and prescription, Wolters Kluwer/Lippincott Williams & Wilkins Health, Philadelphia, 2014.

40.

Piirtola

, Era

Force platform measurements as predictors of falls among older people - a review, Gerontology 52 (2006), 1–16.

41.

Powell

L.E.

, Myers

A.M.

The activities-specific balance confidence (ABC) scale, M28–M, J Gerontol A Biol Sci Med Sci 50A (1995), 34.

42.

Rafal

, Janusz

, Wieslaw

, Robert

Test-retest reliability of measurements of the center of pressure displacement in quiet standing and during maximal voluntary body leaning among healthy elderly men, J Hum Kinet 28 (2011), 15–23.

43.

Rine

R.M.

, Schubert

M.C.

, Whitney

S.L.

, Roberts

, Redfern

M.S.

, Musolino

M.C.

, Roche

J.L.

, Steed

D.P.

, Corbin

, Lin

C.C.

, Marchetti

G.F.

, Beaumont

, Carey

J.P.

, Shepard

N.P.

, Jacobson

G.P.

, Wrisley

D.M.

, Hoffman

H.J.

, Furman

, Slotkin

Vestibular function assessment using the NIH Toolbox, Neurology 80 (2013), S25–S31..

44.

Steffen

T.M.

, Hacker

T.A.

, Mollinger

Age- and gender-related test performance in community-dwelling elderly people: Six-Minute Walk Test, Berg Balance Scale, Timed Up & Go Test, and gait speeds, Phys Ther 82 (2002), 128–137.

45.

Swanenburg

, de Bruin

E.D.

Favero

, Uebelhart

, Mulder

, The reliability of postural balance measures in single and dual tasking in elderly fallers and non-fallers, BMC Musculoskelet Disord 9 (2008), 162.

46.

Tinetti

M.E.

, Speechley

, Ginter

S.F.

Risk factors for falls among elderly persons living in the community, N Engl J Med 319 (1988), 1701–1707.

47.

Toupet

, Ferrary

, Grayeli

A.B.

Visual analog scale to assess vertigo and dizziness after repositioning maneuvers for benign paroxysmal positional vertigo, J Vestib Res 21 (2011), 235–241.

48.

Victoria Hornyak

J.M.V.

Brach

J.S.

Measurement of gait speed, Topics in Geriatric Rehabilitation 28 (2012), 6.

49.

Walker

M.L.

, Austin

A.G.

, Banke

G.M.

, Foxx

S.R.

, Gaetano

, Gardner

L.A.

, McElhiney

, Morris

, Penn

Reference group data for the functional gait assessment, Phys Ther 87 (2007), 1468–1477.

50.

Ward

B.K.

, Agrawal

, Hoffman

H.J.

, Carey

J.P.

, Della

C.C.

Santina, Prevalence and impact of bilateral vestibular hypofunction: Results from the US National Health Interview Survey, JAMA Otolaryngol Head Neck Surg 139 (2013), 803–810.

51.

Whitney

S.L.

, Roche

J.L.

, Marchetti

G.F.

, Lin

C.C.

, Steed

D.P.

, Furman

G.R.

, Musolino

M.C.

, Redfern

M.S.

A comparison of accelerometry and center of pressure measures during computerized dynamic posturography: A measure of balance, Gait & Posture 33 (2011), 594–599.

52.

Whitney

S.L.

, Wrisley

D.M.

, Brown

K.E.

, Furman

J.M.

Is perception of handicap related to functional performance in persons with vestibular dysfunction? , Otol Neurotol 25 (2004), 139–143.

53.

Wrisley

D.M.

, Kumar

N.A.

Functional gait assessment: Concurrent, discriminative, and predictive validity in community-dwelling older adults, Phys Ther 90 (2010), 761–773.

54.

Wrisley

D.M.

, Marchetti

G.F.

, Kuharsky

D.K.

, Whitney

S.L.

Reliability, internal consistency, and validity of data obtained with the functional gait assessment, Phys Ther 84 (2004), 906–918.