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This section presents information on articles related to adapted physical activity. The articles include "Learning through outdoor adventure education," found in an issue of "Teaching Exceptional Children," "Hemispheric specialization and implications for the education of the hearing impaired," found in an issue of "American Annals of the Deaf," and "Modification of spastic gait through mechanical damping," found in an issue of the "Journal of Biomechanics."

Measures describing movement of the center of pressure (CoP) are frequently used to characterize postural control. Estimates of CoP often focus on forces that individuals exert in a single plane through the feet (standing on force plates). However, balance may also be supported by forces other than those developed at the feet, especially when walkers, handrails, and other aids are used. In these cases, it is common to neglect the contributions of handheld supports. Here, we derive and apply equations for an extended CoP that incorporates handhold forces. We then examine the influence of CoP definition (i.e., including or ignoring handhold forces) on common metrics (path length; RMS and maximum excursion; average and maximum velocity) for 12 younger adults with a handrail located lateral to the participants' dominant hand. Participants attempted balance recovery in response to a range of small, medium and large forward and backward platform translations. Significant interactions between perturbation magnitude and CoP definition were found for most metrics. Notably, the interaction of CoP definition and perturbation magnitude significantly affected path length (p-values < 0.001). Post-hoc analyses revealed larger CoP path length when handrail forces were incorporated in CoP estimates compared to ignoring handrail forces at medium (backward: 59.9 vs. 19.0% height; forward: 70.5 vs 22.4% height) and large perturbation magnitudes (backward: 69.9 vs 22.4% height; forward: 103.5 vs 24.6% height). Incorporation of hand forces in CoP calculations can present a different view of postural balance control than relying on a feet-only CoP. This measure could be useful in assessing balance control tasks that involve the use of handrails or hand-held mobility devices., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2020. Published by Elsevier Ltd. All rights reserved.)

The incidence of stairway falls and related injuries remains persistently high; however, the risk of stair injuries could be reduced through improved stairway design. The current study investigated dynamic balance control during stair descent and the effects of varying the step geometry. Data were collected from 20 healthy young and 20 older adults as they descended three staircases (riser heights of 7, 7.5 and 8 inches (178, 190 and 203 mm, respectively)). At each riser height, the tread run length was varied between 8 and 14 inches (203 mm and 356 mm) in one-inch (25 mm) increments. Kinematic data provided measures of segmental and whole-body dynamic control. Results demonstrated that older adults had greater lateral tilt of the upper body than young adults, but actually had larger margins of stability than the young in the antero-posterior direction as a result of their slower cadence. Nonetheless, for both age groups, the longer run lengths were found to provide the largest margins of stability. In addition, increase in run length and decrease in riser height tended to reduce forward upper body tilt. These results help to explain the underlying biomechanical factors associated with increased risk of falls and the relationship with step geometry. Considering the importance of stair ambulation in maintaining independence and activity in the community, this study highlights the definite need for safer stair design standards to minimize the risk of falls and increase stair safety across the lifespan., (Copyright © 2015 Elsevier Ltd and The Ergonomics Society. All rights reserved.)

A new dual-task paradigm was used to investigate age-related differences in attentional dynamics during rapid balancing reactions evoked by small, unpredictable antero-posterior platform movements. The perturbations were delivered while subjects performed a continuous visuo-motor pursuit-tracking task. Onset of significant deviation in tracking was inferred to indicate switching of attentional resources between tracking and balancing tasks. Although tracking deviation was equally likely to occur subsequent to postural perturbation in healthy young and older adults, deviation onset was delayed, on average, by 67% (123 ms) in the older subjects. Delay in onset of tracking deviation correlated with subsequent delay in generating the peak stabilizing postural response at the ankle. These results suggest that impaired attentional dynamics may exacerbate postural instability in older adults.

The need to initiate a step in order to recover balance could, in theory, be predicted by a static model based solely on displacement of the center of mass (COM) with respect to the base of support (BOS), or by a dynamic model based on the interaction between COM displacement and velocity. The purpose of this study was to determine whether the dynamic model provides better prediction than the static model regarding the need to step in response to moving-platform perturbation. The COM phase plane trajectories were determined for 10 healthy young adults for trials where the supporting platform was translated at three different acceleration levels in anterior and posterior directions. These trajectories were compared with the thresholds for step initiation predicted by the static and dynamic COM models. A single-link-plus-foot biomechanical model was employed to mathematically simulate termination of the COM movement, without stepping, using the measured platform acceleration as the input. An optimization routine was used to determine the stability boundaries in COM state space so as to establish the dynamic thresholds where a compensatory step must be initiated in order to recover balance. In the static model, the threshold for step initiation was reached if the COM was displaced beyond the BOS limits. The dynamic model showed substantially better accuracy than the static model in predicting the need to step in order to recover balance: 71% of all stepping responses predicted correctly by the dynamic model versus only 11% by the static model. These results support the proposition that the central nervous system must react to and control dynamic effects, i.e. COM velocity, as well as COM displacement in order to maintain stability with respect to the existing BOS without stepping.

The time course and extent of attentional shifts associated with compensatory balancing reactions were explored using a novel dual-task paradigm. Seated subjects performed a continuous visuomotor tracking task with the hand while the feet simultaneously balanced an inverted pendulum. The pendulum was randomly perturbed, evoking compensatory balance reactions. Changes in tracking performance were held to reflect attentional shifts. Discrete deviation in visuomotor tracking, typically a pause in tracking, began on average 235 ms after the onset of the balance reaction (TA EMG; average latency 90 ms). Such pauses lasted on average 600 ms, although additional errors in tracking lasted up to 9 s following the perturbation. The findings reveal evidence of dynamic shifts in attention associated with distinct phases of compensatory balance control. The initial phase appears to be triggered automatically, whereas later phases involve varying degrees of attentional resources.

Volitional step initiation invariably includes a medio-lateral anticipatory postural adjustment (ML APA), which causes the center of mass (COM) to be propelled toward the stance-limb side prior to the lifting of the swing foot. The present study examined whether this type of anticipatory control plays a functional role in maintaining lateral stability during the rapid compensatory stepping reactions that are evoked when whole-body stability is challenged by unpredictable perturbation. Forward and backward stepping reactions were evaluated in five healthy young adults (ages 22-28) under three task conditions: (1) unconstrained compensatory stepping evoked by platform translation (no specific instructions), (2) constrained compensatory stepping cued by platform translation (prior instruction to step rapidly), and (3) rapid voluntary stepping to a light cue. ML APAs occurred during 70% of perturbation reactions but were too small and brief to have a substantive influence on the lateral movement of the COM occurring during leg lift or swing phase. In contrast, during the light-cued stepping, the ML APA propelled the COM toward the stance-limb side prior to the lifting of the swing limb, and effectively reduced the tendency of the COM to fall toward the swing-limb side during the execution of the step. It is proposed that the presence of an ML APA during compensatory stepping may represent an attempt to preplan a stereotypical stepping response, but that the ability to fully express the anticipatory phase is disrupted by the need to react rapidly to the unpredictable antero-posterior instability imposed by the perturbation. The results suggest that anticipatory control is not the primary mechanism by which the central nervous system deals with the lateral instability arising during rapid compensatory stepping reactions evoked by large, unpredictable antero-posterior perturbation.

Self-initiated leg movement in standing humans is preceded by a medio-lateral preparatory balance adjustment (PBA); however, such preparatory balance control is often absent in reflex-like stepping responses evoked by whole-body instability. The presence or absence of the PBA may reflect a task-dependent modulation of the response serving to preserve lateral stability (PBA present) or avoid delay in the lifting of the foot (PBA absent). To examine whether such task-dependent modulation can occur during more stereotypical limb movements, we examined spinally-mediated withdrawal responses evoked by noxious stimulation of the foot. Results showed that rapid limb withdrawal was preceded by a large PBA when subjects were standing but not when they were supine. The PBA caused limb withdrawal to the noxious stimulation to be delayed. However, the onset of the PBA in the standing trials was equivalent in timing to the onset latency of the classic withdrawal responses recorded during the supine trials. Evidence of a preparatory balance adjustment evoked, in advance of a delayed withdrawal response, at very rapid latencies (underlying muscle activation at 70-120 ms) may raise new questions about the neural mechanisms underlying the co-ordination of balance and movement.

Rapid, reflex-like stepping movements are a prevalent and functional compensatory reaction to destabilization, however, little is known about the underlying control. In this paper, a model is developed to examine how speed and stability demands affect control of foot placement during forward and backward compensatory stepping reactions. The concept of the velocity stability margin (VSM) is introduced to characterize the degree to which the horizontal velocity of the falling body approaches biomechanical limits on the capacity to decelerate the center of mass; analogous limits on center-of-mass displacement are quantified in terms of the displacement stability margin (DSM). The model is used to predict, for any initial step characteristics, the variation in DSM and VSM that would occur as a function of changes in timing of foot placement. The VSM was found to prevail over the DSM in establishing limits of stability. Model simulations demonstrated that there typically exists a minimum swing duration that maximizes speed of response while meeting minimum requirements for stability (VSM > or = 0), as well as a slower speed of response (longer swing duration) at which stability (VSM) is maximized. Experimental data from platform-perturbation tests in 20 healthy young (22-28) and older (65-81) adults were used, in conjunction with the model, to investigate whether speed or stability takes precedence during natural behavior. Control of single-step reactions appeared to favor stability; although the model predicted that a minimally stable step (VSM = 0) could be attained by swing durations as short as 30 ms, the observed swing durations were, on average, 135 ms longer than this, and the average VSM was nearly as large (80%) as the optimally stable value predicted by the model. Control of the initial step of multiple-step reactions was distinctly different. The average swing duration was only 55 ms greater than the minimally stable value and the average VSM was 81% smaller than in the single-step reactions. This reduction in VSM is consistent with a need to execute additional steps and appears to support the validity of the model. This model may help to provide insight into the biomechanical factors that govern the neural control of compensatory stepping reactions.

Change-in-support strategies, involving stepping or grasping movements of the limbs, are prevalent reactions to instability and appear to play a more important functional role in maintaining upright stance than has generally been appreciated. Contrary to traditional views, change-in-support reactions are not just strategies of last resort, but are often initiated well before the center of mass is near the stability limits of the base of support. Furthermore, it appears that subjects, when given the option, will select these reactions in preference to the fixed-support "hip strategy" that has been purported to be of functional importance. The rapid speed of compensatory change-in-support reactions distinguishes them from "volitional" arm and leg movements. In addition, compensatory stepping reactions often lack the anticipatory control elements that are invariably present in non-compensatory stepping, such as gait initiation. Even when present, these anticipatory adjustments appear to have little functional value during rapid compensatory movements. Lateral destabilization complicates the control of compensatory stepping, a finding that may be particularly relevant to the problem of falls and hip fractures in elderly people. Older adults appear to have problems in controlling lateral stability when stepping to recover balance, even when responding to anteroposterior perturbation. Increased understanding and awareness of change-in-support reactions should lead to development of new diagnostic and therapeutic approaches for detecting and treating specific causes of imbalance and falling in elderly people and in patients with balance impairments.

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., Design: Prospective cohort study., Setting: Baseline gait measurements were performed in a gait and balance laboratory; subsequent history of falling was monitored prospectively for 1 year in two self-care facilities., Participants: Fourteen male and 61 female consecutive volunteers (mean age = 82, SD = 6) who were independent in activities of daily living and able to walk 10 m unaided., Measurements: Spatial gait parameters were derived from digitized "footprints"; temporal parameters were derived using footswitches. A clinical activity-based gait assessment was also performed. The dependent variables were pre-existing fear of falling (reported at baseline) and future falling (experiencing one or more falls during the 1-year follow-up)., Main Results: Reduced stride length, reduced speed, increased double-support time, and poorer clinical gait scores were associated with fear but showed little evidence of an independent association with falling. Conversely, increased stride-to-stride variability in stride length, speed, and double-support was associated independently with falling but showed little evidence of relationship to fear. Increased stride width showed some evidence of association with both falling and fear. Stride-to-stride variability in speed was the single best independent predictor of falling., Conclusions: Changes in gait cited previously as risk factors for falling, i.e., decreased stride length and speed and prolonged double support, may in fact be stabilizing adaptations related to fear of falling. Stride-to-stride variability in the control of gait is an independent predictor of falling and may be a useful measure for identifying high-risk individuals and evaluating preventive interventions. Stride width may also be a useful outcome measure. Contrary to common expectation, a wider stride does not necessarily increase stability but instead seems to predict an increased likelihood of experiencing falls.

Previous studies investigating postural control using platform perturbations demonstrated that forward leaning occurs under certain experimental conditions. This study examined a potential benefit of forward leaning, investigating the hypothesis that forward lean acts to increase the effective stiffness of the postural ankle dynamics. A systems modeling approach was used to evaluate the effect of forward lean (4 degrees ankle flexion beyond normal stance) on dynamic postural responses to continuous random antero-posterior platform acceleration in four healthy young adults. Motion was limited to the ankle joint using a restraint device and responses were characterized in terms of center-of-pressure displacement. Also, EMG and kinematic data were used to partition measured ankle torque into impedance and activation (postural "reflex") components. The results failed to show a consistent effect, due to lean, on the ankle dynamics. A significant increase in phasic ankle torque due to increased muscle impedance during forward lean was counterbalanced by a comparable decrease in net "reflex" ankle torque. The change in "reflex" torque was apparently due to decreased phasic dorsiflexor activity in forward lean, since phasic plantarflexor activity did not change significantly. Functionally, the results suggest that forward lean occurs for reasons other than stiffening of the overall postural ankle dynamics.

Age-related changes in the neural, sensory, and musculoskeletal systems can lead to balance impairments that have a tremendous impact on the ability to move about safely. The many complex substrates of the posture control system subserve a common functional goal: regulation of the relationship between the center of mass and the base of support. Traditional approaches, which have focused on the control of the center-of-mass displacement, have documented age-related changes in "feet-in-place" responses: during quiet standing, during volitional movement, or in response to applied perturbation. Recently, increasing attention has been directed toward the control of the base of support, that is, compensatory leg and arm movement, as an important element of the postural repertoire, and early results suggest profound age-related impairment in the control of compensatory stepping movements. For both feet-in-place and stepping responses, control of lateral stability appears to be a major problem associated with increased risk of falling. In view of age-related differences in ability to adapt postural responses under predictable task conditions, future work will likely benefit by mimicking, as much as possible, the varied and unpredictable nature of the events that often precipitate falls in daily life, in order to draw connections between the laboratory or clinic and "real-life" stability.

Previous work suggests that there may be fundamental differences between compensatory stepping responses evoked by postural perturbation and visually cued "volitional" stepping (e.g., gait initiation). In contrast to visual cueing, postural destabilization evokes an array of sensory inputs that are intrinsically linked to the mobilization of rapid compensatory responses. The hypothesis examined in this study was that this fundamental difference would lead to distinct changes in the temporal characteristics of the stepping response. Six healthy young adults were instructed to step quickly in response to either visual cueing or anterioposterior platform motion. Both forward and backward stepping responses were characterized, using measures of vertical ground reaction force. A stereotypical temporal patterning of the stepping response occurred in both stimulus conditions and both directions of stepping, and anticipatory postural adjustments were evident in all trials. However, postural destabilization led to a more rapid initiation and execution of the temporal pattern, in comparison with visually cued responses. The most pronounced effect was seen in the duration of the response, which was reduced by a factor of two, with approximately proportional foreshortening of both the preparatory and swing phases. The results suggest that sensory information conveying a state of instability has a distinct influence on the characteristics of a subsequent stepping reaction. The persistence of the anticipatory postural adjustments suggests that the failure to see this element of the response in previous studies may reflect fundamental differences between volitional and unplanned compensatory stepping.

Healthy young adults (n = 39) were asked to perform four different secondary cognitive tasks during quiet unperturbed stance, in order to investigate the influence of physiological arousal and attention distraction on the control of spontaneous postural sway. During each task, postural activity was quantified in terms of center-of-pressure displacement, leg-muscle activation, and ankle and hip rotation. Arousal was monitored via skin conductance, and questionnaires were used to assess state anxiety. Respiratory trunk movements were also recorded, to assess potential arousal-related destabilizing effects, but failed to show a strong association with the postural measures. The nature of the secondary task affected the postural responses in that subjects tended to lean slightly forward, and exhibited higher levels of activation in tibialis anterior, when performing a mental-arithmetic task. Although this task affected both attention and arousal, the leaning effect was limited to subjects who reported higher levels of anxiety-related autonomic or somatic symptoms during testing, and the degree of leaning was correlated with the level of physiological arousal. A secondary task that diverted attention but did not affect physiological arousal (listening to a spoken-word recording) failed to elicit changes in postural response. These findings suggest that the changes in leaning were associated with task-related changes in physiological arousal, and highlight the need to account for the potentially confounding influence of arousal when studying attentional effects. Given the potential influence on stability, the results also suggest that leaning should be monitored or controlled during balance assessment, particularly when dealing with individuals who may be anxious or afraid of falling.

Objective: To assess the risk of falls attributable to medication use and orthostatic hypotension., Design: Prospective cohort study., Setting: Two self-care, apartment-style residential facilities in the Toronto area., Participants: A total of 100 consecutive older volunteers (mean age = 83, range 62-96) who were independent in activities of daily living and able to stand unaided., Measurements: Prescription medications used by each subject were documented at baseline. Blood pressure measurements were performed supine, immediately after standing, and after 5 minutes. Subjects reported falls weekly, by postcard, for a period of 1 year; nonreporters were contacted by telephone., Results: Fifty-nine percent of subjects fell at least once during the 1-year follow-up. Antidepressant use was associated with an increase in the risk of experiencing one or more falls (RR = 1.6, P = .02). The use of other drug classes examined, including diuretics and sedative-hypnotics, was not associated with an increased risk of falling. Orthostatic hypotension was not predictive of falls. Surprisingly, there was an increase in the diastolic blood pressure of fallers, after 5 minutes, that was not seen in the nonfallers (3.3 vs -0.2 mm Hg, P = .05). Possible explanations for this previously unreported observation are explored., Conclusion: Patients using antidepressants should be followed closely because the risk of falls is increased. Previously reported relationships between benzodiazepines and diuretics and falls are not supported by the present findings. Clinical detection of orthostatic hypotension is unlikely to be useful in predicting future risk of falling.