Postural control and risk of falling in people who are blind: The effect and durability of perturbation and vestibular exercises

Abstract

The aim of this study was to compare the effect and durability of perturbation and vestibular exercises on balance and the risk of falling in people with visual impairment (VI). Thirty-six men with VI were divided into three groups, including a control and two experimental (perturbation and vestibular) groups. The experimental groups performed perturbation and vestibular exercises for 4 weeks and three sessions per week. Biodex balance system was used to assess balance and falling risk before and after training interventions. To evaluate the effects within and between groups at three levels of measurement: pre-test, post-test, and durability effect between three groups, repeated measures analysis of variance (ANOVA) and one-way ANOVA were used. Repeated measures ANOVA test showed that both experimental groups showed significant improvements in static balance, dynamic balance, and falling risk. In comparison between the groups, the results showed that in the post-test and durability stages, there was a significant difference between the groups and the perturbation exercise group had a greater effect on the dependent variables. Due to the effectiveness of exercises, it is recommended that people with VI pay attention to balance-based perturbation exercises to strengthen the somatosensory system and vestibular exercises to strengthen the vestibular system.

Keywords

Balance falling perturbation exercises vestibular exercises visual impairment

Introduction

“Systems theory” has become the basis of researchers’ work to study balance in recent years. In recent years, however, information and findings related to this theory have been used and expanded by other researchers (Horak et al., 1988, 1990; Shumway-Cook & Woollacott, 2007). According to this theory, postural control requires the collection of sensory information to assess the body’s position and movement in space, the ability to produce the forces needed to control body posture, and the complex interaction of nervous and musculoskeletal systems. Role of nervous system in postural control is done through sensory/perceptual processes, which include the visual, vestibular, and somatosensory systems (Mohammadi, 2008).

Information about the position and movement of the head relative to objects around the body is obtained by the visual system (Berencsi et al., 2005), information about the position of the head and its movement relative to gravity is reported by the vestibular system (Shumway-Cook & Woollacott, 2007), and information about the direction of different parts of the body to each other and to the level of reliance is provided by somatosensory inputs (Shumway-Cook & Woollacott, 2007). Vision is of particular importance in motion and balance control and is more important than other sources of information (Paul et al., 2011). Past research has shown that vision plays a major role in maintaining postural stability (Blomqvist & Rehn, 2007) and that lack of vision causes impairment in posture control, limitation of daily activities, and increased risk of falls (Soares et al., 2011).

Blindness is one of the most common disabilities and causes of functional impairment among adults that affects mobility and daily activities (Salomão et al., 2009). A defect in one system is compensated by two other systems. In this situation, it is very important that the remaining senses provide accurate and sufficient information to maintain balance (Wiszomirska et al., 2015). Therefore, it is necessary to develop preventive programs and appropriate treatment and exercise measures to prevent the occurrence and development of problems caused by blindness through the use of the remaining senses (vestibular and somatosensory). There are several reports on the effect of the exercise program on the balance of a person with visual impairment (VI) and whether or not the balance deficit in these individuals improves through exercise (Di Cagno et al., 2018; Mavrovouniotis et al., 2013; Sravani & Metgud, 2014). However, no study has been conducted to compare the effect of two models of perturbation and vestibular exercises on postural control and the risk of falls in a person with VI. Despite the usefulness of other training programs to maintain the daily functional activity of people with VI, researchers in this study have tried to use special training protocols for the somatosensory system (perturbation exercise) and vestibular system (vestibular exercise) that can actively engage the remaining senses. In this regard, it can be assumed that perturbation exercise is a type of exercise in which participants often experience loss of balance to practice and improve the control of balance reactions (Mansfield et al., 2018). Vestibular exercises with the aim of involving the atrial system, make effective use of the sensory system, create a new movement pattern, and improve postural stability (Wiszomirska et al., 2015).

As the main research question, we decide to compare the effect of these two exercise models on the variables of balance and fall risk to find out which exercise model can be more effective and more durable for this group of people who are deprived of their visual system.

Materials and methods

Research design

This study is a quasi-experimental research due to intervening variables, that is, perturbation and vestibular exercise program and purposive sampling of subjects based on inclusion and exclusion criteria and homogeneity of individuals. Subjects were randomly divided into three control and two experimental groups to control the interfering and confounding variables of the effect of exercise programs. It was also an applied research in terms of application of research findings and cross-sectional in terms of implementation time. The statistical population of this study consisted of people in Tehran with VI in the age range of 20 to 30 years. In this study, according to previous researches, using the G-Power sample size estimation equation and considering the test power of 80% and the effect size of 0.78 and the confidence interval of 95%, 36 people were selected and samples were divided into three groups – perturbation exercise group (n = 12), vestibular exercise group (n = 12), and control group (n = 12). In this study, inclusion criteria were: (1) male students with VI in the age range of 20 to 30 years; (2) not participating in other research study; (3) completing informed consent form; and (4) voluntary participation in the research. Exclusion criteria were: (1) history of disease or drug use affecting the nervous system and balance function; (2) having other disability (multiple disabilities); (3) not meeting the requirements of the intervention process; (4) lack of regular attendance; and (5) feeling pain during training.

Experimental variables and assessment protocol

Balance and fall risk index: To evaluate static balance, dynamic balance, and fall risk in this study, a Biodex balance device made in the United States with 12 levels of stability from maximum to minimum stability (1 to 12) and static stability level were used. Static balance (static surface) and dynamic balance (level 8) was repeated for 20 s and three times, with a rest interval of 10 s. The fall risk test was performed in three 20 s tests with a 10 s break between tests and a perturbation range from 12 to 6 level. Validity and reliability of the Biodex device in people who are blind has been confirmed by Aydoğ et al. (2006).

Intervention

Perturbation exercise. In this study, one of the experimental groups participated in perturbation exercises for 4 weeks, three sessions per week, and each session for 60 min (Hurd et al., 2009), which are explained in Table 1. Perturbation exercise tools included the use of a rocker board, roller board, and roller board/platform (Hurd et al., 2009). During this time, the control group was allowed to perform their daily activities (Table 1). During the exercises, in addition to using sports trainers next to the participants to maintain their safety, a rope that was tied around the waist of the participants and hung on the ceiling wall was used to avoid any sudden falls and accidental lack of balance.

Table 1.

Perturbation exercise.

	Rocker board	Rollerboard/platform	Rollerboard
Sets/duration	2–3 sets/1 min each	2–3 sets/1 min each; performed bilaterally	2–3 sets/30 s–1 min each
Direction of board movement	A/P, M/L	Initial: A/P, M/L Progression: diagonal, rotation	Initial: A/P, M/L Progression: diagonal, rotation
Application	Begin in bilateral stance for first session. Perform in single leg stance for remaining sessions	Subject force is counter-resistance opposite of rollerboard, matching intensity and speed of application, so rollerboard movement is minimal. Leg muscles should not be contracted in anticipation of perturbation, nor should response be rigid co-contraction.	Begin in bilateral stance for first session. Perform in single-leg stance for remaining sessions. Perturbation distances are 1–2 inches

A/P: anterior/posterior; M/L: medial/lateral.

Vestibular stimulation exercise. The other experimental group participated in vestibular exercises for 4 weeks, three sessions per week, and each session for 50 min, which is explained in Table 2. At all stages of the exercises, the researcher with verbal feedback next to the samples, prevented any sudden event that would endanger the samples, and with physical feedback, tried to make the samples perform the exercises in a real way.

Table 2.

Vestibular-stimulating exercise.

Practice situation	Exercise	Repetition	Practice time
1– Standing static balance	Standing upright	2	30 s
	Single leg stance	4	30 s
	Weight shift	1	10 times
	Sit to stand	1	10 times
	Rotate 360 degrees and then sit	1	10 times
2– Forward ambulation	Feet apart, yaw head turns	1	20 head turns
	Feet apart, pitch head turns	1	20 head turns
	Tandem, head still	1	20 feet
3– Backward ambulation	Feet apart, head still	1	20 feet
	Feet apart, yaw head turns	1	20 head turns
	Tandem, head still	1	20 feet
	Ambulation with turns	1	20 times
4–Sitting	Shoulder shrugging and circling	1
	Bending forward and picking up objects from ground	1	20 times
	Bend side to side and pick up objects from ground	1
	Changing from sitting to standing	1
5– Head movements	Bending forward and backward to touch chin to chest.	1
	Moving head 45 degrees to left and right	1	20 times
	Moving head 90 degrees to left and right	1

Ethics approval. Before starting the research process, all participants completed and approved the individual and informed consent form to participate in the research. This study also has an ethics code with the number IR.UT. SPORT.REC.1398.035 on 2019/07/15 from the Research Ethics Committee of the Faculty of Physical Education, University of Tehran.

Statistical method

Descriptive statistics (such as mean and standard deviation) were used to describe and organize the research data. In the inferential statistics section, the normality of data distribution was evaluated by Shapiro–Wilk test and homogeneity of variance was evaluated by Leven test. Repeated measures ANOVA and one-way ANOVA was used to evaluate the intra-group and inter-group effects at three levels of pre-test, post-test, and the effect of durability between the three groups (control and experimental groups). All statistical analyses were performed by SPSS software version 24 at a significance level of .05.

Results

The results of the subjects’ demographic information are shown in Table 3. ANOVA test also showed that the p-value in the indices of age, weight, and height was equal to (.764), (.089), (.680), respectively, which indicates the homogeneity of descriptive information between the three groups (Table 3). Shapiro–Wilk test was used to determine the normality of data distribution due to the number of samples being smaller than 50. The results of this test showed that the distribution of all measured data was normal.

Table 3.

Demographic information of the subjects in three groups.

Variable	Group(N = 12)	Mean	SD	p
Age (years)	PerturbationVestibularControl	23.0823.4123.75	2.392.391.81	.764
Weight (kg)	PerturbationVestibularControl	67.5865.3367.16	2.393.281.80	.089
Height (cm)	PerturbationVestibularControl	169.75168.75170.08	3.253.334.77	.680

Static balance index: Both experimental (perturbation and vestibular training) groups have demonstrated significant improvements from the pre-test–post-test, from pre-test–follow-up in the static balance variable (p < .05).

Dynamic balance index: Both experimental (perturbation and vestibular training) groups have demonstrated significant improvements from the pre-test–post-test, from pre-test–follow-up, and post-test–follow-up in the dynamic balance variable (p < .05).

Fall risk test: Both experimental (perturbation and vestibular training) groups have demonstrated significant improvements from the pre-test–post-test, from pre-test–follow-up, and post-test–follow-up (just perturbation training) in the fall risk index (p < .05). But in the control group, no significant difference was observed between different measurement stages in all variables (Table 4).

Table 4.

Scores and results of repeated measures ANOVA and one-way analysis of variance.

Variables	Time	Pre-test	Post-test	Follow-up	Intragroup differences
Variables	group	Mean (SD)	Mean (SD)	Mean (SD)	p
OSI static	PerturbationVestibularControl	3.5 (1.5)3.55 (1.27)3.54 (1.55)	1.96 (1.17)* 1.83 (1.64)* 3.33 (1.46)	2.15 (1.17) 2.01 (1.49) 3.6 (1.4)	.003.004.864
Between-group differences		0.997	000.1^a	000.1^b
APSI static	PerturbationVestibularControl	3.79 (1.53)3.09 (1.55)3.49 (1.56)	1.7 (1.28)* 1.79 (1.2)* 3.61 (1.43)	1.72 (1.26) 1.94 (1.19) 3.65 (1.45)	.021.035.352
Between-group differences		0.669	000.1^a	000.1^b
MLSI static	PerturbationVestibularControl	1.72 (0.27)2.01 (0.33)1.76 (0.27)	1.38 (0.24)0.9 (0.2)1.7 (0.26)	1.47 (0.23)1.52 (0.17)1.85 (0.26)	.486.364.282
Between-group differences		0.758	0.073	0.461
OSI dynamic	PerturbationVestibularControl	6.15 (2.83)6.3 (2.75)6.19 (2.72)	2.85 (1.78)* 3.04 (1.94)* 5.47 (2.55)	3.45 (1.94), * 3.54 (2.25), * 6 (2.85)	.003.009.534
Between-group differences		0.990	000.1^a	000.1^b
APSI dynamic	PerturbationVestibularControl	4.68 (2.77)4.4 (2.78)4.82 (2.67)	1.6 (1.16)* 2.19 (1.19)* 4.63 (2.53)	2.02 (1.2), * 2.58 (1.22), * 4.6 (2.55)	.007.027.293
Between-group differences		0.923	000.1^a	000.1^b
MLSI dynamic	PerturbationVestibularControl	2.89 (1.4)2.55 (1.23)2.83 (0.3)	1.01 (0.94) * 1.55 (1.13) * 2.68 (1.37)	1.3 (0.85), * 2.03 (1.18), * 2.8 (1.27)	.011.050.731
Between-group differences		0.808	000.1^a	000.1^b
FRT	PerturbationVestibularControl	4.7 (0.54)4.75 (0.9)4.95 (0.82)	1.9 (0.24)* 1.78 (0.06)* 4.06 (0.39)	2.5 (0.21), * 3.05 (0.35)** 4.34 (0.44)	.025.041.249
Between-group differences		0.971	000.1^a	000.2^b

ANOVA: analysis of variance; OSI: overall stability index; APSI: anterior–posterior stability index; MLSI: medial–lateral stability index; FRT: fall risk test.

Shows the difference between groups in the post-test stage (p < .05).

Shows the difference between groups in the follow-up stage (p < .05).

p < .05: Bonferroni test results from pre– post-test.

p < .05: Bonferroni test results from pre–follow-up.

***

p < .05: Bonferroni test results from post-test–follow-up.

Considering Table 4, the results of one-way analysis of variance in post-test and follow-up test showed a significant difference between the groups in all variables of postural control and fall risk (p < .05) except Medial–Lateral Stability Index (MLSI) of static surface (p > .05). Tukey’s test was used to determine which groups differed. Tukey’s test showed that there was no significant difference between perturbation exercises and vestibular exercises in post-test and durability effect in terms of the score of static Overall Stability Index (OSI), static Anterior–Posterior Stability Index (APSI), all dynamic surface index including OSI, APSI, and MLSI (p > .05). Also, a significant difference was found between perturbation and control group (p < .05) and vestibular and control groups (p < .05) in the post-test and the durability effect of the mentioned tests in people with VI. Based on the effect size scale of perturbation exercise on the postural control variable in six areas, it was reported as 0.922, 0.736, 0.022, 0.496, 0.468, 0.479 and the fall risk variable was reported to be 0.394, respectively, which is regarded a large effect size. Also, based on the size effect scale of vestibular exercise on the postural control variable in six areas, it was reported as 0.698, 0.662, 0.038, 0.356, and 0.225 and fall risk variable of 0.274, respectively, which shows a size effect smaller than the perturbation group.

Discussion

This research aimed at evaluating the effectiveness and durability of perturbation and vestibular exercises on balance control and the risk of falls in a person with VI. The results of this study showed that both perturbation and vestibular experimental groups had better performance in static balance, dynamic balance, and falling risk variables, but the control group did not show any significant changes at different stages of measurement. Comparing the effect size and the mean scores obtained in the two exercise groups, it should be stated that perturbation exercises compared to vestibular exercises had a greater effect on balance control variable and fall risk index and were more effective than the vestibular and control groups.

The results of this study are consistent with the results of studies by Desai, Jovin Chien (Chien & Hsu, 2018), Krasilshchikov (Krasilshchikov et al., 2018) in terms of the effectiveness of perturbation exercises on reducing the risk of falls and improving balance and motor function of individuals in different groups. Parita Desai et al. (2018) evaluated the effect of balance-based perturbation exercises on the risk of falls and balance in the elderly in the age range of 65–80 years. The results showed that the perturbation exercise program had a positive effect on reducing the risk of falls and improving the performance of static and dynamic balance in the open and closed eyes. He stated that one of the reasons for effectiveness is improving the function of muscle recall and increasing the readiness of these individuals to deal with sudden perturbation (Desai et al., 2018). Restoration of balance after a perturbation in the body position (for example, compensatory walking, or taking objects) can be achieved by rotation of the body or compensatory movements. Exercise that specifically aims to improve balance may be more effective than general exercise (Mansfield et al., 2018). The ability to react quickly after losing balance is essential to prevent falling. It has previously shown that perturbation-based balance training can prevent falls in older adults and people with Parkinson’s (Pijnappels et al., 2005). Turbulence during perturbation exercises is intended to mimic the accidental and unexpected nature of falls in people’s daily lives, and this type of exercise ensures that the specific approach to work conforms to the “learning feature” hypothesis (Gerards et al., 2017). During unexpected balance perturbation, effective muscle momentum must be generated from many joints to control displacement of the center of gravity and prevent falls (Nakamura et al., 2001). This speed and effectiveness of muscle activation, especially of the lower limbs, is very important to avoid falling and maintaining balance during an unforeseen perturbation on slippery and unstable surfaces to maintain the body’s center of gravity in the target range (De Freitas et al., 2010). The use of external perturbation is thought to teach involuntary reactions, which is the key to reduce falling in people when the external balance in daily life is disturbed. Therefore, in confirmation of previous research, it can be said that due to the special approach to perturbation training, which is to mimic the random and unexpected nature of daily activities, it was able to have a positive significant impact on improving balance performance and reducing the risk of falling in perturbation training group compared to control group. In another section, the findings of this study were consistent with the results of studies (Chang et al., 2008; Samoudi et al., 2015; Sunderman, 2016; Wiszomirska et al., 2015) on the importance of vestibular exercises.

According to previous studies, vestibular rehabilitation is one of the most important treatments for balance disorders (Macias et al., 2005). Research has shown that people with VI have higher risks of falls and imbalance injuries than normal people. Studies show that a proper rehabilitation program compared to medication can play an important role in reducing peripheral dizziness and improving balance disorders (Ghasemi et al., 2010). One of these rehabilitation programs is vestibular exercises that can be useful in the treatment of unilateral, bilateral, balance disorders, and control or reduction of symptoms such as dizziness, nausea, vomiting, etc. (Farzin et al., 2018). In fact, it can be inferred that vestibular rehabilitation provides the necessary stimuli for central sensory reorganization and integration, thereby, improving control of the body’s proper posture through the three mechanisms of substitution, adaptation, and habit. Also it allows the brain to preserve the balance and reduce the risk of fall symptoms (Tavanai & Hajiabolhassan, 2013). Regarding the mechanisms of research results, it can be pointed out that since proper balance is created by the interaction of inputs from the visual systems, vestibular involvement, and subsequently appropriate motor responses are created that are sent to the eyes and spinal cord in the form of reflexive instructions. Performing vestibular exercises can lead to the proper functioning of these three systems and ultimately lead to improved postural control and balance in people with VI. Thus, in confirmation of previous research, it can be said that due to people with VI relying on other senses, by strengthening each of these senses, the balance and motor function of people with VI is improved.

For comparing intergroup effects, results of one-way analysis of variance in post-test and follow-up effect showed significant differences between groups in all variables of postural control and fall risk (p < .05) except medial–lateral static index (p > .05). Tukey’s test showed that there was no significant difference between perturbation exercises and vestibular exercises in post-test and follow-up effect in terms of the score of overall stability surface index, posterior–anterior stability index, overall dynamic surface index, dynamic posterior–anterior index, and dynamic medial–lateral index (p > .05). However, despite the insignificance of the difference between the two groups of perturbation and vestibular exercise, researchers used the effect size of exercise. Comparing the effect size of these exercises, it can be concluded that perturbation exercises have a greater effect on postural control and fall risk index than vestibular exercises.

One reason for the effectiveness of perturbation exercises may be that people with VI are able to compensate for their VI by activating their proprioceptive system. This sense may play a greater role in maintaining the vertical alignment of the body in situations similar to everyday life in people with VI and thus compensate for the lack of visual system. Because in situations similar to the daily life of people with VI, more fluctuations occur and the threshold of stimulation of the vestibular system is higher, and these people will use the somatosensory system. Thus, when people with VI are aroused by unexpected and challenging reactions in different directions during perturbation exercises, it engages the somatosensory system and often the results can show a significant and greater improvement over vestibular exercises. So people with VI in static and non-exercise situations use the vestibular system to meet their postural control needs. The main reason can be mentioned that a blind person uses the vestibular sensory system to meet his needs and this system is active automatically; however, practicing the ability to improve the somatosensory system relative to the vestibular system is more visible in less active people who are blind. It is believed that the perturbation-based balance training program mentioned in this research protocol has further improved the factors evaluated in this research because these exercises challenge balance control in different ways and perturbation are unpredictable; therefore, adaptations that rely on predictive control are avoided.

It should be noted that this study was designed for people who are blind and the results cannot be generalized to all people with VI. Lack of access to visually impaired and partially sighted people was one of the main limitations of this study. However, it seems that the use of perturbation and vestibular exercises can also be effective for people with VIs (low vision and partial vision). To ensure generalizations of results, it is suggested that this research design be reviewed for people who are partially sighted and with low vision and compared with the results of this study. By conducting such research and evaluating the effectiveness of exercise, it is possible to suggest the use of perturbation and vestibular exercises for people with different spectrums of VI in daily life.

Conclusion

The findings of this study showed a significant improvement in increasing balance and reducing the risk of falling in people who are blind and performed vestibular and perturbation exercises. People with VI, despite their VI, can improve other systems involved in balance control, including the vestibular and somatosensory system, through related exercises. According to the results of this study, it seems that people with VI can develop the function of their vestibular system through vestibular exercises, so it is recommended that people with VI pay attention to the vestibular system through vestibular exercises in the balance training program. Participating in perturbation-based balance training can increase somatosensory performance, so the researcher’s recommendation is that people with VI pay attention to perturbation-based balance exercises to strengthen their somatosensory system to improve their athletic performance, balance, and reduce falls.

Footnotes

Acknowledgements

The authors would like to express their sincere gratitude to the children and their parents who participated in this study.

Author contributions

Conceptualization and methodology by Mohammad Hani Mansori, Yousef Moghadas Tabrizi, and Mohammad Karimizadeh Ardekani; investigation done by all authors; writing the original draft by all authors; writing, review, and editing by all authors; software, data curation, and data analysis by all authors; article submission by Mohammad Hani Mansori.

Declaration of conflicting interests

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

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This article was extracted from the MSc thesis of the Department of Sports Medicine and Health, Faculty of Physical Education and Sport Sciences, University of Tehran.

Ethics approval

All ethical principles were considered in this article and this study was approved by the Ethics Committee of the Faculty of Physical Education of Tehran University (Code: IR.UT. SPORT.REC.1398.035).

Consent to participate

An individual and informed consent form was used to ensure the satisfaction of individuals and their parents to participate in the research.

ORCID iD

Mohammad Hani Mansori

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