Brian E. Maki

Gait changes in older adults: predictors of falls or indicators of fear

OBJECTIVE: To determine, in a cohort of ambulatory older adults, whether spatial‐temporal measures of foot placement during gait can predict the likelihood of future falls or whether these measures are more likely to be indicative of adaptations associated with pre‐existing fear of falling.

Aging and postural control : A comparison of spontaneous- and induced-sway balance tests

Two different balance testing methods were compared: (1) measurement of spontaneous postural sway during quiet standing, and (2) measurement of induced postural sway in response to an applied postural perturbation. Eyes‐open tests were performed in 64 healthy young and elderly adults and in five elderly subjects with a history of falling. In both balance tests, the sway was defined in terms of the displacement of the center of pressure on the feet. Spontaneous sway was quantified using a number of different amplitude‐ and frequency‐based parameters. Induced sway was measured in response to anterior‐posterior acceleration of a platform on which the subject stood. The induced‐sway test was specially designed to be safe and nonthreatening for elderly subjects; thus, the platform perturbation was confined to small accelerations and a gentle pseudorandom motion was used. To derive a measure of postural stability, the data from this test were fitted with a model that was then used to predict the response to sudden (transient) perturbations, thereby simulating the response in actual falls. Although both induced‐ and spontaneous‐sway measures demonstrated significant aging‐related decreases in stability, the differences were more pronounced for the induced‐sway data. Conversely, some of the spontaneous‐sway measures were much more successful in distinguishing the fallers from the nonfallers. There was a significant correlation between induced‐sway and certain spontaneous‐sway measures in the normal young adults; however, in the elderly normals and fallers, the data from the two types of balance tests either showed no correlation or, for certain spontaneous‐sway measures, tended to show an inverse relationship.

Are Activity‐Based Assessments of Balance and Gait in the Elderly Predictive of Risk of Falling and/or Type of Fall?

To determine whether an activity‐based test of balance and gait is predictive of the risk of: (1) falling in situations that are related to specific tasks evaluated as part of the test, (2) experiencing falls precipitated by different classes of biomechanical events, or (3) falling in general; and to compare the predictive ability of the activity‐based test for the falls described in (2) and (3) to that of a posturography test that has been found previously to be predictive of falling risk.

Effect of a Perturbation-Based Balance Training Program on Compensatory Stepping and Grasping Reactions in Older Adults: A Randomized Controlled Trial

Background Compensatory stepping and grasping reactions are prevalent responses to sudden loss of balance and play a critical role in preventing falls. The ability to execute these reactions effectively is impaired in older adults. Objective The purpose of this study was to evaluate a perturbation-based balance training program designed to target specific age-related impairments in compensatory stepping and grasping balance recovery reactions. Design This was a double-blind randomized controlled trial. Setting The study was conducted at research laboratories in a large urban hospital. Participants Thirty community-dwelling older adults (aged 64–80 years) with a recent history of falls or self-reported instability participated in the study. Intervention Participants were randomly assigned to receive either a 6-week perturbation-based (motion platform) balance training program or a 6-week control program involving flexibility and relaxation training. Measurements Features of balance reactions targeted by the perturbation-based program were: (1) multi-step reactions, (2) extra lateral steps following anteroposterior perturbations, (3) foot collisions following lateral perturbations, and (4) time to complete grasping reactions. The reactions were evoked during testing by highly unpredictable surface translation and cable pull perturbations, both of which differed from the perturbations used during training. Results Compared with the control program, the perturbation-based training led to greater reductions in frequency of multi-step reactions and foot collisions that were statistically significant for surface translations but not cable pulls. The perturbation group also showed significantly greater reduction in handrail contact time compared with the control group for cable pulls and a possible trend in this direction for surface translations. Limitations Further work is needed to determine whether a maintenance program is needed to retain the training benefits and to assess whether these benefits reduce fall risk in daily life. Conclusion Perturbation-based training shows promise as an effective intervention to improve the ability of older adults to prevent themselves from falling when they lose their balance.

Early activation of arm muscles follows external perturbation of upright stance

Grasping, counterbalancing and protective arm movements are an important defence against external postural perturbation, but are commonly constrained in studies of postural control. We measured muscle activity at the shoulder, and the lower leg, during unconstrained responses to platform translation. Results revealed very early activation in shoulder muscles, similar in timing to the automatic ankle responses. The arm activation occurred even when the reaction provided no immediate defence against destabilization but would appear to be more than a startle response, since the activation was scaled to the perturbation magnitude and persisted even when perturbations were expected. The arm activation would appear to be driven from a remote sensory source, since there was negligible loading or stretch of the arm muscles.

Do anticipatory postural adjustments precede compensatory stepping reactions evoked by perturbation

Many recent studies have revealed the consistency of anticipatory postural adjustments preceding single leg movements, such as stepping, in standing humans. These adjustments appear to involve an active lateral transfer of weight to the stance leg. The present study demonstrates that these anticipatory adjustments often do not appear in compensatory stepping responses evoked by postural perturbation. Compensatory stepping without anticipatory active weight transfer seemed to be more likely to occur when stepping was not pre-planned or when the perturbation characteristics were novel. The substantial variability seen in the anticipatory weight transfer, when it did occur, contrasts the consistency of the anticipatory responses seen in gait initiation and other non-compensatory leg movements. The results suggest that there may be fundamental differences in the control of compensatory versus non-compensatory stepping, and may provide insight into the sequencing of anticipatory postural reactions and subsequent leg movements.

The 'deceleration response' to transient perturbation of upright stance

Characterizing the postural perturbation due to a transient support-surface displacement in terms of acceleration and deceleration events leads to a new framework for understanding the control of the stabilizing response. This study documents the existence of a deceleration response, which has not been reported previously, and explores the control of this response by varying the predictability of the timing and pattern of support-surface deceleration. Control features related to the capacity of the subject to predict deceleration were exposed, in part, by including novel tri-phasic perturbations, in which the normal deceleration phase was replaced by a re-acceleration. In all trials, subjects showed a marked response to the onset of deceleration. The capacity of predict the timing and pattern of deceleration had a significant influence on the deceleration response, as well as the tonic muscle activation that preceded the onset of deceleration.

Does frontal-plane asymmetry in compensatory postural responses represent preparation for stepping ?

The bilateral symmetry of feet-in-place responses to postural perturbations in the anterior-posterior direction has not been well studied. This paper presents evidence that right- and left-leg responses that appear to be approximately symmetrical in the sagittal plane may actually involve an asymmetry in the frontal plane, namely, a lateral weight shift. Comparison with trials where subjects stepped suggests that these lateral weight shifts represent early preparations for stepping responses that are aborted before the foot is actually lifted. Thus, it would seem that compensatory stepping involves a sequence of discrete modifiable stages, rather than a single immutable motor program. Moreover, postural responses that appear to be similar in the sagittal plane may actually be seen to involve quite different postural strategies, i.e. in terms of preparation for stepping, when viewed in the frontal plane.

Determining the Visual Angle of Objects in the Visual Field: An Extended Application of Eye Trackers

Many eye-tracker systems display the point of central gaze fixation on video images of the viewed environment. We describe here a method for determining the visual angles of objects located in the periphery. Such data are needed to study the potential contributions of peripheral vision during cognitive and motor tasks.

Influence of handrail height on the generation of stabilizing forces and moments

Although changes in handrail design parameters might affect the energy requirements and speed of stairway gait, there is little doubt that the primary consideration in handrail design lies in the prevention of falling accidents. The overall objective of this work is to evaluate the effects of changes in handrail design on stairway safety. Due to time constraints, the present study was limited to an investigation of handrail height, although there is no reason why the present experimental paradigm could not be used to study other handrail parameters.