A Conceptual Framework for the Progression of Balance Exercises in Persons with Balance and Vestibular Disorders

  

    
 
    
VOR x1
    
VOR x2
  
  

    
Firm, Feet Apart, 1meter, White Background
    
1
    
3
  
  

    
Firm, Feet Apart, 3meter, White Background
    
2
    
 
  
  

    
Firm, Feet Apart, 1 meter, Complex Background
    
4
    
6
  
  

    
Firm, Feet Apart, 3meter, Complex Background
    
5
    
 
  
  

    
Activities are ranked numerically in    order of increasing difficulty. 
      
VOR: Vestibulo-Ocular Reflex.
      
Repeat sequence with: Firm, Romberg (7 -    12); Firm, Semi-tandem Romberg    (13 - 18);
      
Firm, Tandem Romberg (19-24); Foam, Feet Apart (25 - 30); Foam, Romberg (31 - 36);
      
Foam, Semi-tandem Romberg (37 - 42); Foam, Tandem (43 - 48).
      
 
  

Table 5:  Vestibulo-Ocular Reflex Progression.

Foot Stance

We ranked the following five stances in order of increasing difficulty as the base of support becomes narrower: feet apart, feet together, semi-tandem Romberg, tandem Romberg, and single leg stance. Meulbauer et al. (2012) studied healthy young adults while maintaining stability in four stances including feet apart, staggered stance, tandem stance, and single leg stance. Participants stood on a firm computerized balance platform with eyes open and as the base of support was reduced, the center of pressure displacements significantly increased [23]. In this framework, each of the exercise categories applies the principle of increasing the challenge of an exercise by narrowing the base of support except for the weightshifting exercise category, where the feet apart stance was maintained throughout the progression.

Surface

Several studies have shown that balance is more challenged when standing on compliant compared to firm surfaces [24, 25]. Additionally, an increase in the surface slope adversely affects postural stability during standing [26] and when a person stands on a slope surface the risk of falling increases because of the high friction force between the feet and the surface [27]. Redfernet al. (1993) compared the effect of downhill and uphill walking on postural stability and found that people tend to slip more often while walking downhill due to the increased load of friction force at heel strike [28]. Persons with bilateral vestibular loss demonstrated very large and fast postural sway compared to individuals without vestibular deficits when standing on an inclined surface with eyes closed, which reflects difficulty interpreting surface orientation based on somatosensory inputs alone [29].

This information, along with the input from clinical experts, led us to hypothesize that the degree of difficulty and the amount of postural sway increases in the following order for surface progression: firm, firm with incline, firm with decline, and foam. This sequence was used for the modified center of gravity exercise category and the firm to foam progression was used in the VOR and weight shifting categories.

Visual Input

Vision affects postural control across all populations [30]. In a study of elite athletes, increased postural sway was observed with eyes closed activities compared to eyes open [25]. During visual sway referencing experiments it has been shown that older adults yield increased postural sway compared to younger adults, indicating that older adults have greater visual dependence [31]. For a person with vestibular loss, the effect of removing visual input results in decreased postural control, especially when standing on an unstable surface [29]. Because of the negative correlation between visual input and performance, we deemed activities completed with eyes closed to be more challenging than activities with eyes open in the proposed framework. This consideration can be applied to all categories except for the VOR category, as the exercises in this category necessitate that the eyes are open.

Static vs Dynamic Standing

Within the framework highlighted in Appendix 1, we consider the effects of dynamic weight-shifting and upper extremity movements that lead to changes in center of gravity. Available research and clinical experience was used to hypothesize that weight-shifting activities in the medial-lateral direction are easier than the anteriorposterior direction with feet apart. This was primarily based on the work of Winter et al. (1996), which concludes that during quiet stance with feet apart, the hip muscles primarily control postural stability in the medial-lateral direction, where as the ankle muscles control balance in the anterior-posterior direction [32]. Because the base of support during feet apart stance is greater in the medial-lateral direction, a larger COP displacement is required to disrupt postural stability in this direction. Theoretically this would make this activity less challenging than maintaining COP in a smaller base of support where a smaller displacement may cause imbalance due to movement beyond the base of support. Additionally Chou et al. (2009) have demonstrated that subjects show better directional control in the medial-lateral direction than in the anterior-posterior direction when tasked with reaching to targets displayed on a screen during weight shifting assessments using the Neuro com Smart Balance Master ^®system, [33]. Not surprising, it has been shown that ankle range ofmotion is an important factor related to balance and functional ability [34, 35] and increased risk of falling is related to poor medial-lateral control [32, 36]. Although postural stability has not been analyzed during weight shifting at different speeds and distances, we propose that postural sway will increase when the speed of the movements is decreased. Additionally, we propose that postural sway increases as the center of mass extends beyond the base of support [37].

In the development of the BES Test, Horak et al. (2009) investigated the type of balance control system that is associated with different balance diagnoses and results showed that individuals with somatosensory deficits had worse anticipatory postural adjustments [22]. One activity used to assess anticipatory postural control in the BES Testis lifting a weight to shoulder level. Inour framework, we chose to include bilateral shoulder flexion, with and without weight, to achieve exercises that modify center of gravity. We hypothesized that completing this task with heavier weights will elicit greater postural sway compared to completing the task with a lighter weight or no weight. Based on our clinical experience, we hypothesize that lifting the weight at slow speeds will cause more sway compared to faster speeds.

Head Movements

Head movements often provoke visual blurring, dizziness, imbalance and path veering in patients with peripheral vestibular hypofunction, resulting in limited head movements while walking [14]. Cohen et al. (2014) found that both healthy controls and individuals with vestibular hypofunction are able to maintain postural stability for increased durations with static head position compared to completion of yaw and pitch head movements [24]. In subjects with vestibulopathy, visual acuity degrades as a consequence of head movement, presumably because the vestibular-ocular reflex cannot stabilize the gaze [38]. Mamoto et al. (2002) found that patients with unilateral and bilateral vestibular involvement adopted head stabilization as a strategyto maintain gaze stability [39]. It has also been shown that patients with vestibular disorders had a higher percentage of lower (worse) scores on the Dynamic Gait Index in the yaw plane compared to the pitch plane during gait [40]. We therefore proposed that head movements in the yaw direction are more challenging than balance activities incorporating head movements in the pitch direction. No head movement was subsequently deemed the easiest condition of the three variations. In our framework, head movement considerations were used for progressing static standing, compliant surface, gait, and the VOR exercise categories.

Dual Tasks

Improved performance would be expected with focused attention toward the task when compared to an activity that is completed with a cognitive or manual dual task challenge [41]. Silsupadol et al. (2006) include examples of both cognitive and manual dual task challenges in their case report which investigated dual task training in older adults with balance impairments [42]. Examples of cognitive tasks include, but are not limited to, naming words within an identified category, counting backwards, arithmetic, memorization, and spelling tasks for cognitive tasks.Reaching, throwing/catching a ball, kicking a ball, and carrying an objectare some examples of manual tasks [42]. We included manual dual tasks within our framework in each of the buckets except for weight shifting.

Redfern et al. (2004) found that patients with well compensated vestibulopathies require increased attention compared with healthy controls when performing a balance task concurrently with a cognitive task. The effect of the cognitive task had a greater negative impact on performance as the difficulty of the postural task increased [43]. When choosing balance and gait related tasks, the clinician needs to consider whether the elements of the task demand voluntary movement, an autonomic postural response, or an anticipatory postural adjustment. Patients need to be challenged with a combination of all three conditions for optimal recovery [44]. During the development of this framework, the expected postural response elicited by each exercise was deliberated with the goal to encompass each type of response in the framework.

Environment

We acknowledge that many different environmental variables can alter performance and impact the degree of challenge for an exercise. Some of the considerations include whether the exercise is completed in settings that are: quiet or loud; empty or crowded; high or low contrast; and predictable or unpredictable [45, 46]. Additionally, the following factors can affect performance: the type of compliant surface (foam density, carpet type, outdoor grass or rocky surfaces,slope and variability of uneven surfaces, slippery surfaces); the lighting (fluorescent, iridescent, sunlight, dimlight); the presence or absence of physical assistance (from the support of a physical therapist, family member, assistive device, or even a wall or other stable object/surface for support); and the tone/inflection of the tester in providing instructions or commands [45]. Our framework includes progression of the surface the exercises are completed on. The adoption of this type of framework in the clinical setting should consider the additional variables that simulate the real world environment for the client.

Gait

The goal of gait training is to assist the patient in mastering walking on level surfaces and then challenge the patient with progressive variations in the task or environment, while working toward the same quality of independent controlled locomotion [47]. Patients with vestibular involvement typically ambulate with a wide base gait, decreased gait speed, and limited head movement [39,48,49]. All of the considerations discussed so far can be applied to gait exercises to alter the challenge. Additionally, we included the speed at which someone walks in our framework, where the research and clinical experience guided our decision to progress from self-selected speed to a fast speed, and to a slow speed in order of increasing difficulty [50,51]. We also propose based on clinical experience that walking backward is more difficult than walking forward. Although not included in our framework we recognize that additional gait variations can be included to challenge a patient such as: changing gait speeds, quick stops/starts, stepping over objects of different sizes, sidestepping, braiding, marching, completing 180 and 360 degree turns, walking on toes, or walking on heels [52].

Special Considerations for Eye/Head Exercises

The VOR, when functioning normally, acts to maintain stable vision during head motion and consists of two components: the angular and linear VOR [53]. The angular VOR is controlled by the semi-circular canals and is primarily responsible for gaze stabilization. The critical stimulus for recalibration of the dynamic VOR response following unilateral vestibular loss is the presence of motion of images on the retina during head movements. Adaptation of the VOR gain is a dynamic process that requires visual experience for its acquisition [54].

Gaze stabilization exercises are an example of adaptation exercises used to improve the gain of the VOR [55]. This exercise progression begins with the VOR X 1 viewing paradigm involving the use of a stationary target at a distance of 1 meter against a plain background while performing either pitch or yaw head movements. The patient is instructed to keep his/her eyes fixed on a target and move their head side to side as fast as they can as long as the target remains stationary and in clear focus. Patients are instructed to slow the speed of their head if the target is moving or blurring consistently. Examples of exercise variations include changing the stance position, the stance surface, the distance of the target, the background from plain to complex [55].

Additionally, VOR exercises can be completed via VOR X 2 viewing where the target and head both move, but in opposite directions. In this case, the target and head velocity are equal, but opposite in direction, thereby requiring an angular VOR eye velocity twice as large as head velocity, stimulating a large change in the angular VOR [55]. There is evidence that the VOR gain can increase with gaze stability exercise in individuals with vestibular hypofunction [55]. Herdman et al. (2003) found that significant improvements in dynamic visual acuity occurred in adults with unilateral vestibular hypofunction who completed vestibulo-ocular reflex exercises [55].

Substitution exercises are used to treat patients with bilateral peripheral vestibular hypofunction [56]. In this treatment approach, patients are taught to primarily rely on visual and somatosensory cues to maintain postural stability in place of absent vestibular inputs. When there is bilateral peripheral vestibular weakness, but not complete loss, both adaptation and substitution exercises are utilized to maximize function. In a study involving saccade and VOR motor learning, it was concluded that both saccade and vestibular ocular motor systems are adaptable and can work together to optimize gaze stability in persons with bilateral vestibular loss [57].

Therefore, we believe that corrective saccades are an important substitution exercise for patients with bilateral and unilateral vestibular loss. Exercises are used to promote the use of saccadic eye movements for gaze stability by teaching patients to move their eyes to a target while the head is stationary. General guidelines for vestibular exercises to improve gaze stability and balance exercises to improve postural stability following unilateral and bilateral peripheral vestibular hypofunction have been outlined by Herdman et al. (2001) but there are limited reports on how vestibular physical therapists translate the principles into practice [58]. Most exercise programs are customized to the deficits of the patient [12, 59]. Customized exercise appears to be superior to handing patients a standard written exercise handout [8].

Not described specifically in our progression, but sometimes utilized, are exercises for visual vertigo [60]. Vittae et al. [61], Szturm et al. [7], and Pavlou [59] have suggested that exposure to increasingly more complex visual scenes can promote changes in the VOR gain. Recently, optokinetic stimulation has been used with persons with mal de debarquement [62]. Any of the exercises already described can be augmented with these visually complex backgrounds, such as virtual reality [63, 64], head-fixed visual stimuli apparati [65], or optokinetic scenes [7, 59].

Discussion

Ultimately, the goal of balance rehabilitation is to improve patients’ daily lives. However, improvement is contingent on intense, challenging, and progressive task-specific training [66]. Furthermore, motor learning is necessary if betterment of functional performance is desired. Karni et al. (1998) have shown that motor learning is achieved following practice on the order of minutes [67]. If a few minutes of practice is required for skill acquisition, and 30 second training segments are used with the proposed framework, it would be logical to complete 4 - 6 repetitions of each exercise, however specific volume parameters have not been established [68]. Evidence indicates that balance training 2 - 3 times per week is recommended for healthy adults and older adults [68-70].

When adopting a balance progression framework into clinical practice, the timing of progressing to the next exercise is important. We believe that this should occur when the individual’s postural control is stable enough that they perceive the challenge of the task to be minimal and the postural sway is consistently within the limits of stability during multiple repetitions of the exercises. Mastery of static postural control involves maintaining balance in a position with minimal sway, no loss of balance and no external support [47]. Therefore, an exercise would not be considered to have been mastered if an individual steps out of stance position, touches the wall or other surface to maintain balance, or requires hands on assistance from the physical therapist for safety or to prevent falling. Additionally, we suggest that the patient’s perception of their performance should be considered in the determination of when to progress to a more difficult exercise.

For clinical application it is important to realize that people undergoing any type of exercise program may plateau. In efforts to avoid boredom with repeated attempts at a particular exercise, or frustration associated with failure of an exercise, we propose that an individual who is unable to pass a particular exercise should revisit the preceding exercise within the category. If they succeed, they should retry the initially failed exercise. If they again fail to master that task, they should move ahead to the next task to see if this difficulty is secondary to that specific individual, or may be due to an error in our proposed progression schema.

An additional clinical application consideration is related to the method by which the clinician ensures that their patient is achieving the appropriate speed. This could be related to cadence during ambulation, speed of head movement with dynamic head turning or VOR completion, weight shifting speed, or extremity movement speed for modified center of gravity exercise. Our team suggests the use of a metronome or verbal cues from the clinician to achieve the desired speed.

In 2011, the American College of Sports Medicine (ACSM) published guideline aimed to guide individualized exercise prescription. The ACSM guidelines used data from randomized controlled trials to support the optimal volumes, patterns, and progressions they proposed for performing aerobic and resistance exercises. However, these specific recommendations are stated as "not known" for neuro motor exercise prescription [68]. Examples of guidelines for aerobic exercise progression include increasing volume of metabolic equivalents or pedometer step counts at a pattern of certain minutes per day with progression of duration, frequency, and intensity increases [68]. Within the resistance exercise guidelines for progressing, percentages of the 1 repetition maximum is used, with increasing sets and repetitions, and progressions of greater resistance, increased repetitions, and increased frequencies [68].

The framework has some limitations that we have identified. We recognize that not every possible variable is depicted for each exercise category and, as discussed above, many environmental considerations may affect the complexity of a task. Additionally, personal characteristics may alter the challenge and/or tolerance for a task differently amongst individuals. Factors that may affect success of a vestibular physical therapy program include: age, distal sensation, medical co-morbidities, drug regime, visual deficits, magnitude of vestibular loss, cognition, psychiatric co-morbidities [71], and attitude about the exercise program. There is also the issue of consistency of performance within each subjects’ training program that is difficult to control for (i.e. effects of stress on their daily performance). These stressors may include both positive and negative outside life events, subjective perception of being in the state of a "good" or "bad" day. Subsequently, individual personality differences and the type of coping mechanism they utilize, may impact how the stressor impacts their performance. In addition to the magnitude of vestibular loss, we expect that the stage of recovery could also impact consistency (i.e. someone who is well compensated might not fluctuate in terms of balance as much as an individual who is uncompensated).

Another limitation is related to differences in baseline performance. It is necessary to complete some assessment exercises to determine where each individual should start within each category. The fact that some of the progressions have not been tested and validated presents added limitation to the framework. Finally, baseline strength differences may cause misunderstanding about how light and heavy weight affect balance challenge within the modified center of gravity category. By defining standard amounts for the light weight conditions (one pound) and heavy weight conditions (three pounds), we may see the light weight is actually very challenging, or perceived as heavy, for one person and the heavy weight could be no challenge, or perceived as light, to another person.

Future exploration in application of this framework with technologists has the potential to support the development of telerehabilitation balance exercises programs, including programs that leverage home-based technologies such as the Wii Fit [72] and sensory augmentation [73]. Using a structured balance exercise progression in a telemedicine based program may be an alternative way to provide additional rehabilitative services for patients with balance impairments who have limited access to physical therapy secondary to insurance or geographical restrictions.

Conclusion

A theoretical balance exercise framework has been presented. The rationale and structure of building increased complexity to an exercise program for a person with a balance and/or vestibular disorder was detailed. The understanding and utilization of a balance exercise hierarchy has the potential to improve patient care and the quality of clinical research trials. We suggest that clients should be provided exercises based on their presenting complaints and deficits and progressed throughout the sequence within the given exercise category to optimally challenge their balance. High level exercises are included in this framework to allow for adequate intensity which aims to avoid an under dosed exercise program. While much effort was spent hypothesizing the hierarchy of balance exercises in this framework, future research is needed to validate, or reorganize, the order in which we progress individuals with balance and vestibular disorders. Instead of performing a handful of the same exercises repetitively, the proposed balance sequence enables patients to be challenged by a multitude of exercise variations. The novel exercises may stimulate improved exercise motivation and compliance supporting the overall goal of skill acquisition.

Acknowledgement

Research reported in this publication was supported by the Exploratory/Developmental Research Grant of the National Institutes of Health under the award number: R21DC012410. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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