James S. Frank

The Balance Evaluation Systems Test (BESTest) to Differentiate Balance Deficits

Background: Current clinical balance assessment tools do not aim to help therapists identify the underlying postural control systems responsible for poor functional balance. By identifying the disordered systems underlying balance control, therapists can direct specific types of intervention for different types of balance problems. Objective: The goal of this study was to develop a clinical balance assessment tool that aims to target 6 different balance control systems so that specific rehabilitation approaches can be designed for different balance deficits. This article presents the theoretical framework, interrater reliability, and preliminary concurrent validity for this new instrument, the Balance Evaluation Systems Test (BESTest). Design: The BESTest consists of 36 items, grouped into 6 systems: “Biomechanical Constraints,” “Stability Limits/Verticality,” “Anticipatory Postural Adjustments,” “Postural Responses,” “Sensory Orientation,” and “Stability in Gait.” Methods: In 2 interrater trials, 22 subjects with and without balance disorders, ranging in age from 50 to 88 years, were rated concurrently on the BESTest by 19 therapists, students, and balance researchers. Concurrent validity was measured by correlation between the BESTest and balance confidence, as assessed with the Activities-specific Balance Confidence (ABC) Scale. Results: Consistent with our theoretical framework, subjects with different diagnoses scored poorly on different sections of the BESTest. The intraclass correlation coefficient (ICC) for interrater reliability for the test as a whole was .91, with the 6 section ICCs ranging from .79 to .96. The Kendall coefficient of concordance among raters ranged from .46 to 1.00 for the 36 individual items. Concurrent validity of the correlation between the BESTest and the ABC Scale was r=.636, P<.01. Limitations: Further testing is needed to determine whether: (1) the sections of the BESTest actually detect independent balance deficits, (2) other systems important for balance control should be added, and (3) a shorter version of the test is possible by eliminating redundant or insensitive items. Conclusions: The BESTest is easy to learn to administer, with excellent reliability and very good validity. It is unique in allowing clinicians to determine the type of balance problems to direct specific treatments for their patients. By organizing clinical balance test items already in use, combined with new items not currently available, the BESTest is the most comprehensive clinical balance tool available and warrants further development.

Fear of falling and postural control in Parkinson's disease

This study investigated the relationship between fear of falling (FOF) and qualitative and quantitative postural control in Parkinsons disease (PD). Fifty‐eight nondemented PD patients were studied along with age‐matched healthy controls. The degree of FOF was estimated using the Activities‐specific Balance Confidence scale. Qualitative postural control was evaluated using a component of the Unified Parkinson Disease Rating Scale. Postural control was quantified, using centre of pressure measures obtained from a force plate, for eight standing balance tests of different challenges. The results showed that FOF was more evident for PD patients when compared with healthy individuals of similar age. Furthermore, FOF was significantly associated with a qualitative estimate of postural control in PD; individuals with PD who had a greater degree of posture impairment reported greater FOF. The results also showed that an estimate of FOF may help to explain quantitative postural instability in PD. FOF, when coupled with a qualitative estimate of postural control, was able to explain a greater amount of variation in quantitative balance performance for five of the eight balance tests. When considered independently, the qualitative measure of postural control, in general, could not well predict quantitative balance performance. The greater degree of FOF and its possible association with altered postural control suggests that FOF should be considered as an important, independent risk factor in the assessment and treatment of postural instability in patients with PD.

Kinematic and kinetic validity of the inverted pendulum model in quiet standing

Movements of the whole-body center of mass during quiet standing have been estimated from measurements of body segment movements. These whole-body center of mass movements have been compared with movements of the center of mass as predicted from a simple inverted-pendulum model of standing. However, the total body center of mass is a weighted average of the center of mass of all individual body segments. The question arises as to how well the total body center of mass represents the individual segments and lower limb joint angles. This study focuses on the validity of how well the individual segments and lower limb angles temporally and spatially synchronize with the total body center of mass. Eleven healthy university students volunteered to participate. Kinematic data were collected using a 3D optoelectronic camera system; kinetic data were collected using a 3D force plate. Participants stood quietly, with eyes open, for 120 s. Segment and whole body centers of mass were calculated from a 14 segment, 3D bilateral model. Segment and joint angles were calculated for the lower limbs, bilaterally, and the trunk. Segment center of mass root-mean-square displacements were strongly correlated with center of mass height relative to the ankle joint and were synchronized, or temporally locked, to the movement of the whole body center of mass. Sagittal plane ankle angular displacements were highly correlated to sagittal plane center of mass movement; stronger correlations between body center of mass and lower limb angular displacement were observed, the result of compensatory knee joint angular displacements. These data support and extend the use of an inverted pendulum model to represent quiet standing postural control.

Fear of falling modifies anticipatory postural control

This study investigated the influence of fear of falling or postural threat on the control of posture and movement during a voluntary rise to toes task for 12 healthy young adults. Postural threat was modified through alterations to the surface height at which individuals stood (low or high platform) and changes in step restriction (away from or at the edge of the platform) creating four levels of postural threat: LOW AWAY, LOW EDGE, HIGH AWAY and HIGH EDGE. To rise to the toes, an initial postural adjustment must destabilise the body so that it can be moved forward and elevated to a new position of support over the toes. Centre of pressure and centre of mass profiles, as well as tibialis anterior (TA), soleus (SO) and gastrocnemius (GA) muscle activity patterns were used to describe this behaviour. The results showed that the performance of the rise to toes task was significantly modified when positioned at the edge of the high platform. In this situation, the central nervous system reduced the magnitude and rate of the postural adjustments and subsequent voluntary movement. Although the duration of the movement was lengthened for this most threatening condition, the sequencing and relative timing of TA, SO and GA muscle activity was preserved. These changes in rise to toes behaviour were accompanied by evidence of increased physiological arousal and participant reports of decreased confidence, increased anxiety and decreased stability. Evidence of fear of falling effects on anticipatory postural control is clinically relevant as it may explain deficits in this control observed in individuals with balance disorders. For example, individuals with Parkinson’s disease or cerebellar dysfunction demonstrate impaired performance on the rise to toes task as reflected in alterations of both the timing and magnitude of their anticipatory postural adjustments. Our findings suggest alterations in the magnitude of postural adjustments may be magnified by fear of falling while changes in the timing of postural adjustments may reflect underlying pathology.

Balance in chronic low back pain patients compared to healthy people under various conditions in upright standing

OBJECTIVE To determine whether balance responses of chronic low back pain patients differed from healthy controls under various upright standing conditions which challenged the balance system. METHODS Eight chronic low back pain patients and eight controls performed seven postural tasks which involved manipulation of visual, vestibular, and proprioceptive input as well as body orientation. The unbiased root mean square, the mean power frequency and the mean position of the centre of pressure were calculated from force plate readings. A pain scale and two questionnaires were used to evaluate the severity of disability and the scores were correlated with the force plate measures. The reliability of the force plate measures was determined. RESULTS A significant increase in the root mean square in the medial-lateral direction for the chronic low back pain patients as a group was found during tasks which involved removal of vision, especially when combined with increased task complexity. The root mean square and mean power frequency in the medial-lateral plane were reliable for the majority of the tasks. CONCLUSION The root mean square in the medial-lateral direction was reliable and sensitive enough to measure an increase in postural sway of chronic low back pain patients as a group compared to healthy controls when the task involved increased complexity and removal of visual information. RELEVANCE A reliable measure of whole body performance obtained during simple postural tasks, such as the root mean square in the medial-lateral plane, may be used to distinguish chronic low back pain patients as a group from a healthy population. Further uses may include the development and guidance of chronic low back pain treatment and evaluation of recovery progress.

Sampling duration effects on centre of pressure summary measures.

The purpose of the present study was to examine the effect of sample duration on the magnitude and reliability of centre of pressure (COP) summary measures commonly used to characterize the control of upright stance. COP was recorded from 49 participants who stood quietly during three consecutive 120 s trials. Each record was subdivided into 15, 30, 60 and 120 s samples and root mean square (RMS), mean power frequency (MPF) and mean position of COP were calculated for each sample. RMS significantly increased and MPF values significantly decreased as sample duration increased. Substantial increases in the reliability of both RMS and MPF were observed with increased sample duration.

Influence of event anticipation on postural actions accompanying voluntary movement

SummaryThe central organization of anticipatory postural adjustments was investigated by examining the influence of preparatory set on the temporal relationship between postural and arm (focal) muscle activation. Surface EMG was recorded from the right tibialis anterior, lateral gastrocnemius, anterior deltoid and posterior deltoid muscles when pushing or pulling on a stiff handle. Preparatory set was manipulated by informing the subject of the upcoming direction of responding with a 80, 50 or 20% certainty. This created high, neutral and low levels of preparatory set, respectively. All six subjects showed activation of postural muscles in advance of focal muscles for both push and pull responses. However, only three subjects showed the expected effect of preparatory set on reaction time performance, i.e., an increase of reaction time with decreasing response probability. For these three subjects, the time between the activation of postural and focal muscles was the same for the high and neutral levels of preparatory set, but increased with a low level of preparatory set. The increased postural-focal latency for the low preparatory set condition was due to a longer delay for the activation of the focal muscles but not the postural muscles. This finding suggests that anticipatory postural adjustments and the activation of focal muscles are triggered by separate motor commands.

Influence of a visuo-spatial, verbal and central executive working memory task on postural control.

In this study, participants were required to perform different working memory (WM) tasks (a verbal task, a visuo-spatial task with two levels of difficulty and a central executive task) under different challenges to postural control (sitting, shoulder width stance and tandem stance). When a WM task was added, changes in postural sway were characterized by an increase in frequency and decrease in amplitude of sway indicating a tighter control. We found no changes in postural control between the different types of WM tasks, which might support a general capacity limitation hypothesis. However, no changes were found in performance of the WM when postural stance was modified and no changes were found in postural sway, when the difficulty level of the visuo-spatial task was modified. Consequently, the results seem to indicate that the addition of a WM task, regardless of task type or task difficulty, forces the central nervous system to choose a tighter control strategy.

Postural compensations to the potential consequences of instability: kinematics

Abstract Previous work has shown that central set can significantly affect postural control. Fear of falling, which is based on the perceived risk of injury as a result of instability, may act as a contributing source of central set. This study addressed an essential component of fear of falling by manipulating central set and altering postural threat. Eight healthy male subjects (23±5.67 years) were exposed to five repeated external perturbations under conditions which modified the consequences of a loss of balance: a non-threatening environment in which subjects stood at ground level (LO), and a threatening environment (HI) in which they stood at the edge of an elevated platform (0.76±0.05 m). Two questions were of interest: How is the centre of mass regulated when there is an increased threat to a loss of balance? Is the ability to habituate to repeated perturbations affected by an increased threat to a loss of balance? The results demonstrated that the strategy for postural control is influenced by environmental constraints that alter postural threat, and that habituation to repeated perturbations occurs independent of the potential consequences of instability. Two subjects stepped following the initial perturbations delivered in the LO condition. When the potential consequences of a loss of balance were more severe, seven of the eight subjects enforced tighter control over centre of mass (COM) kinematics. Specifically, the COM starting position was more posterior, the range of COM displacement was significantly reduced and the time to peak COM velocity occurred significantly earlier. Habituation of the postural response was demonstrated in both conditions as a progressive increase in COM displacement with repeated perturbations. These findings contribute to a better understanding of the effects of central set on postural control and provide insight into how postural control is managed by individuals who are concerned with the consequences of a loss of balance.

Dopaminergic modulation of timing control and variability in the gait of Parkinson's disease

The basal ganglia have been implicated in timing control, yet the nature of timing disturbances in Parkinsons disease (PD) is poorly understood. We evaluated the influence of timing cues on spatiotemporal aspects of gait control and its variability, and the impact of dopaminergic treatment on timing. Three separate groups: 19 PD (OFF state); 24 PD (ON state); and 30 control participants were tested. Participants walked on a computerized carpet at four randomized and metronome‐controlled rates: self‐paced, 60, 80, or 100 steps/min. To our knowledge, this is the first study to demonstrate that medicated PD patients had poorer timing control than patients withdrawn from medication and healthy participants when modulating timing to an external stimulus. Increased step‐to‐step timing variability and deficits in mean temporal gait characteristics revealed that the medicated PD group (in contrast to nonmedicated PD group) performed least like healthy participants. This was observable in externally‐cued conditions, but not during self‐paced gait. Similar to previous research, step length contributed to overall slowness in PD, while temporal characteristics of gait did not. Interestingly, healthy participants increased stride length with each increase in cue rate, whereas both PD groups locked their step length regardless of temporal demand. Step‐to‐step variability differences between PD and healthy (e.g. step and double‐support time measurements) may be indicative of specific basal ganglia involvement in temporal control of gait.