Background and framework

Falls are the leading cause of injury and premature death among community dwelling older adults, with about a third of community-living elderly above 65 years falling every year (1-3). In Denmark, more than 45,000 hospital contacts each year are related to falls and a third of these involves fractures (4). For elderly, the cost of falling includes distress, pain, injury, loss of confidence, and ultimately loss of independence and mortality (3). Prevention of falls is therefore an urgent public health challenge (5). 

Impaired balance alone is associated with a 40% increase in risk of falls but is at the same time modifiable through exercises (6, 7). International consensus states that balance exercise should be structured and individually tailored, but no consensus exist how to tailor an individualized exercise intervention (8). This lack of individualizing may explain why currently applied exercise programs aimed at improving balance only reduce falls by 17 - 20% (5, 7, 9, 10).

Horak and colleagues recently developed the Balance Evaluation System’s Test (BESTest), which groups balance items into six “systems” (11). By measuring each “system” as a separate property of postural control, the BESTest can be applied to guide how to focus the intervention when aiming at improving balance. No other current balance measure offers this applicability (12-14).

Because the execution time of the BESTest is rather extensive a shorter version of the test “the mini-BESTest” was developed applying a Rasch analyses (15, 16). This methodological approach ensures uni-dimensionality of the test, but because the inclusion of items in the Rasch analysis is based on item functioning in relation to the total score the original division in subsystems is jeopardized (15).

A brief version of the original BESTest was developed based on item with total correlation (17). The “Brief BESTest” retains the theoretical framework of the original test, including only a single item to measure each “system” but shows limited sensitivity to change and the item selection is disputable (18).

Consequently, no instruments have until now provided a clinical applicable approach for designing and prescribing individualized balance exercise interventions for individuals who are in risk of falls.

Specific Training According to BaLance Evaluation (STABLE) is developed to meet this demand. STABLE is built on the framework of the BESTest, but essential properties of the two approaches are different. In STABLE, six functional measures are applied to quantify the individuals’ balance ability within six specific domains of balance.

In the following, we briefly explain how these six measures relates to the “systems” of the BESTest and the domains in STABLE. For detailed description of the six tests please refer to the measure section. To learn how the measures are applied to guide exercise prescription please refer to introduction to stable.

Power

The “system” Biomechanical constraints comprises in the original BESTest of items which primarily measure strength of the lower extremities plus a rating of the individual’s alignment, deformities and pain based on the therapist visual assessment. The reliability of these ratings is not satisfactory (11) and it is questionable which exercises (if any) are effective to target these properties when impaired.

In STABLE, this domain is measured applying a sit-to-stand test. Sit to stand tests are generally accepted as a measure of lower extremity strength and basic biomechanical function (19, 20) and the test is an independent predictor of fall risk (21).

Because the sit-to-stand test measures strength by the force developed within a timespan this domain is named Power.

Stability limits

Stability limits/Verticality is evaluated in the BESTest in sitting by leaning bilaterally and in standing applying “the functional reach test” (22) forward and laterally. Limits of stability can be defined as to how far an individual is able to extend their center of mass relative to their base of support without stepping, slipping or falling (23, 24). In STABLE, this domain is measured applying a reach test wherein the individual chose the preferred strategy of exploring the stability limits reaching toward a wall. This approach is chosen to improve the reliability and validity of the original reach test (25-27).

Because of the narrowed focus, this domain is named Stability limits.

Anticipatory turning

Transitions-Anticipatory Postural Adjustments is the third “system” of the BESTest. This property of balance is necessary in almost every daily tasks and has been reported as one of the most frequent cause of falling if ineffective (28). In the BESTest, five subtests are covering this “system”. Our proposal is that, if a single task is to cover this domain meaningfully, this task should be essential for daily living and closely related with the risk of falls.

Turning is a fundamental component of mobility being associated with 35–45% of steps in common everyday tasks and therefore a very frequently performed task requiring effective anticipatory postural adjustments (29). Difficulties in turning and low turning speed has been identified as a predictor of falls (30-33). The risk of falls is proportional to the turning angle and is up to three times higher during turning compared to straight walking (34). Active head or whole-body turning is often included in protocols to evaluate balance and mobility in elderly individuals (35-37). Thus, a measure of turning ability is therefore included in STABLE as the core expression of an individual’s ability of executing anticipatory postural adjustments.

Because of the specified focus in this property of balance, this domain is named anticipatory turning.

Reactive stepping

Reactive balance, the ability to recover from instability through a rapid postural muscle corrective response, step, or grasp (38), is a critical components of balance for fall avoidance (39) and inefficient stepping response is highly correlated with falls (40).

In the BESTest, reactive postural response is evaluated by releasing isometric pressure against the patient in different directions. This “push and release” technique, originally developed for patient´s who has Parkinson´s disease (41), is a clinical version of the lean and release protocol, which has been applied to investigate reactive postural responses (42-44). Applying this approach, stepping strategy among elderly is very adaptable within the same testing session (45, 46) and manually providing pressure and releasing in a consistent manner is very difficult (47-49). Consequently, we propose a different clinical approach for evaluation reactive stepping strategy.

The Four Square Step Test evaluates rapid stepping in multiple directions (31). The original test does not measure reactive stepping per se, because the individual is instructed to repeat a stepping task in a beforehand practiced pattern, enabling the individual to use anticipatory balance strategies. Thus, in STABLE a modified version of the test is applied wherein the individual is stepping in unpredictable directions as commanded by the assessor. In contrary to the push and release technique, observed deficits in this modified test logically translate into exercises for improving reactive stepping strategy which can be performed by the patient without the need for assistance.

Because of the specified focus in this property of balance, this domain is named reactive stepping.

Sensory orientation

The vertical perception and body orientation depend on how spatial information is encoded and how spatial reference frames are selected and weighted. The ability to orient in space and keeping verticality therefore depends on the interaction between allocentric (primary visual), egocentric (primary proprioceptive) and geocentric (primary vestibular) reference frames (50).

In the BESTest sensory orientation is measured with the modified Clinical Test of Sensory Interaction in Balance (CTSIB-m) (51) and an “incline test”. The reliability of the latter is very low (11). The CTSIB-m was developed as a clinical low-cost alternative to the force plate-based gold standard (52-54), but further modifications are warranted to improve the validity of the test (55, 56). Therefore, in STABLE we apply an extended version of the original CTSIB-m, which measures balance in 12 combinations of foot positions, visual and proprioceptive conditions systematically challenging all three reference frames.

Cognitive-motor interaction

Stability in gait is the sixth “system” of the BESTest and is measured with the dynamic gait index and the timed “up and go” test performed with and without a secondary cognitive task (11).

Gait is an inevitable task of daily living and improving stability in gait is often a core goal of any balance exercise program rather than a property of balance. Indeed, some evidence exist that gait is a construct independent from balance (57). Thus, in STABLE we do not regard stability in gait as an isolated domain of balance.

Instead we propose focusing this domain on cognitive-motor interaction in balance. As in the BESTest, we apply the timed “up and go” test with a dual-task paradigm to measure this domain. Dual-task-related changes in gait is highly related with falls and is an accepted measure of cognitive-motor interaction in balance (58, 59). Further, we have modified the test to control how the individual prioritizes between tasks. This modification is essential because when individuals with balance impairment execute dual-task paradigms it is inconsistent whether the primary (i.e. the “up and go” task), the secondary (i.e. the cognitive task) or both tasks are affected. Differences between individuals and change over time can thus only be measured meaningfully when monitoring both tasks (60, 61).

Because of the distinct focus, this domain is named cognitive-motor interaction.

 

To learn more please refer to introduction to STABLE

 

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