Crossover Steps Research Articles

Enantioselective Synthesis of α‐Aryl Ketones by a Cobalt‐Catalyzed Semipinacol Rearrangement

AbstractA highly enantioselective cobalt‐catalyzed semipinacol rearrangement of symmetric α,α‐diarylallylic alcohols is disclosed. A chiral cobalt‐salen catalyst generates a highly electrophilic carbocation surrogate following hydrogen atom transfer and radical–polar crossover steps. This methodology provides access to enantioenriched α‐aryl ketones through invertive displacement of a cobalt(IV) complex during 1,2‐aryl migration. A combination of readily available reagents, silane and N‐fluoropyridinium oxidant, are used to confer this type of reactivity. An exploration into the effect of aryl substitution revealed the reaction tolerates para‐ and meta‐halogenated, mildly electron‐rich and electron‐poor aromatic rings with excellent enantioselectivities and yields. The yield of the rearrangement diminished with highly electron‐rich aryl rings whereas very electron‐deficient and ortho‐substituted arenes led to poor enantiocontrol. A Hammett analysis demonstrated the migratory preference for electron‐rich aromatic rings, which is consistent with the intermediacy of a phenonium cation.

Enantioselective Synthesis of α-Aryl Ketones by a Cobalt-Catalyzed Semipinacol Rearrangement.

A highly enantioselective cobalt-catalyzed semipinacol rearrangement of symmetric α,α-diarylallylic alcohols is disclosed. A chiral cobalt-salen catalyst generates a highly electrophilic carbocation surrogate following hydrogen atom transfer and radical-polar crossover steps. This methodology provides access to enantioenriched α-aryl ketones through invertive displacement of a cobalt(IV) complex during 1,2-aryl migration. A combination of readily available reagents, silane and N-fluoropyridinium oxidant, are used to confer this type of reactivity. An exploration into the effect of aryl substitution revealed the reaction tolerates para- and meta-halogenated, mildly electron-rich and electron-poor aromatic rings with excellent enantioselectivities and yields. The yield of the rearrangement diminished with highly electron-rich aryl rings whereas very electron-deficient and ortho-substituted arenes led to poor enantiocontrol. A Hammett analysis demonstrated the migratory preference for electron-rich aromatic rings, which is consistent with the intermediacy of a phenonium cation.

Influence of aging on the relation between head control and hip joint kinematics during crossover stepping.

Falls in older individuals are a serious health issue in super-aged societies. The stepping reaction is an important postural strategy for preventing falls. This study aimed to reveal the characteristics of lateral stepping in response to mechanical disturbance by means of an analysis of the hip joint kinematics in the stepping leg and head stability during crossover steps. The participants included 11 healthy older and 13 younger individuals. An electromagnet-controlled disturbance-loading device induced crossover steps due to lateral disturbance. Responses were measured using a motion capture system and force plates. The righting reaction of the head was quantified by lateral displacement (sway), neck joint kinematics (angle displacement, angular velocity), and neck joint moment during crossover stepping. Moreover, the relationship between the neck lateral bending moment and angular velocity of hip flexion/adduction of the stepping leg was examined. The lateral head sway was significantly larger in the older participants (1.13±0.7 m/s2) than in the younger individuals (0.54±0.3 m/s2); whereas, the angle displacement (older -14.1±7.1 degree, young -8.3±4.5 degree) and angular velocity (older 9.9±6.6 degree/s, 41.2±27.7 degree/s) of the head were significantly lower in the older than in the younger participants. In both groups, the moment of neck lateral bending exhibited a significant negative correlation with the hip flexion angular velocity of the stepping leg. Correlation analysis also showed a significant negative correlation between the neck lateral bending moment and hip adduction angular velocity only in the older group (r = 0.71, p<0.01). In conclusion, older individuals increased instability in the lateral direction of the head and decreased righting angle displacement and angular velocity of the head during crossover steps. The correlation between neck moment and hip flexion/adduction angular velocity suggested a decrease in step speed due to increased neck muscle tone, which could be influenced by vestibulospinal reflexes.

A Lightweight Island Model for the Genetic Algorithm over GPGU

This paper presents a parallel approach of the genetic algorithm (GA) over the Graphical Processing Unit (GPU) to solve the Traveling Salesman Problem (TSP). Since the earlier studies did not focus on implementing the island model in a persistent way, this paper introduces an approach, named Lightweight Island Model (LIM), that aims to implement the concept of persistent threads in the island model of the genetic algorithm. For that, we present the implementation details to convert the traditional island model, which is separated into multiple kernels, into a computing paradigm based on a persistent kernel. Many synchronization techniques, including cooperative groups and implicit synchronization, are discussed to reduce the CPU-GPU interaction that existed in the traditional island model. A new parallelization strategy is presented for distributing the work among live threads during the selection and crossover steps. The GPU configurations that lead to the best possible performance are also determined. The introduced approach will be compared, in terms of speedup and solution quality, with the traditional island model (TIM) as well as with related works that concentrated on suggesting a lighter version of the master-slave model, including switching among kernels (SAK) and scheduled light kernel (SLK) approaches. The results show that the new approach can increase the speed-up to 27x over serial CPU, 4.5x over the traditional island model, and up to 1.5–2x over SAK and SLK approaches.

Stepping strategies of young adults undergoing sudden external perturbation from different directions

Stepping strategies following external perturbations from different directions is investigated in this work. We analysed the effect of the perturbation angle as well as the level of awareness of individuals and characterised steps out of the sagittal plane between Loaded Side Steps (LSS), Unloaded Medial Steps (UMS) and Unloaded Crossover Steps (UCS). A novel experimental paradigm involving perturbations in different directions was performed on a group of 21 young adults (10 females, 11 males, 20–38 years). Participants underwent 30 randomised perturbations along 5 different angles with different levels of awareness of the upcoming perturbations (with and without wearing a sensory impairment device) for a total of 1260 recorded trials. Results showed that logistic models based on the minimal values of the Margin of Stability (MoS) or on the minimal values of the Time to boundary (Ttb) performed the best in the sagittal plane. However, their accuracy stayed above 79% regardless of the perturbation angle or level of awareness. Regarding the effect of the experimental condition, evidences of different balance recovery behaviours due to the variation of perturbation angles were exposed, but no significant effect of the level of awareness was observed. Finally, we proposed the Distance to Foot boundary (DtFb) as a relevant quantity to characterise the stepping strategies in response to perturbations out of the sagittal plane.

Differential Evolution Based Simulated Annealing Method for Vaccination Optimization Problem

Infectious diseases pose a severe threat to human health, especially the outbreak of COVID-19. After the infectious disease enters the stage of large-scale epidemics, vaccination is an effective way to control infectious diseases. However, when formulating a vaccination strategy, some restrictions still exist, such as insufficient vaccines or insufficient government funding to afford everyone's vaccination. Therefore, in this paper, we propose a vaccination optimization problem with the lowest total cost based on the susceptible-infected-recovered (SIR) model, which is called the Lowest Cost Of Vaccination Strategy (LCOVS) problem. We first establish a mathematical model of the LCOVS problem. Then we propose a practical Differential Evolution based Simulated Annealing (DESA) method to solve the mathematical optimization problem. We use the simulated annealing algorithm (SA) as a local optimizer for the results obtained by the differential evolution algorithm (DE) and optimized the mutation and crossover steps of DE. Finally, the experimental results on the six data sets demonstrate that our proposed DESA can achieve a more low-cost vaccination strategy than the baseline algorithms.

An Improved Grey Wolf Optimizer Based on Differential Evolution and OTSU Algorithm

Aimed at solving the problems of poor stability and easily falling into the local optimal solution in the grey wolf optimizer (GWO) algorithm, an improved GWO algorithm based on the differential evolution (DE) algorithm and the OTSU algorithm is proposed (DE-OTSU-GWO). The multithreshold OTSU, Tsallis entropy, and DE algorithm are combined with the GWO algorithm. The multithreshold OTSU algorithm is used to calculate the fitness of the initial population. The population is updated using the GWO algorithm and the DE algorithm through the Tsallis entropy algorithm for crossover steps. Multithreshold OTSU calculates the fitness in the initial population and makes the initial stage basically stable. Tsallis entropy calculates the fitness quickly. The DE algorithm can solve the local optimal solution of GWO. The performance of the DE-OTSU-GWO algorithm was tested using a CEC2005 benchmark function (23 test functions). Compared with existing particle swarm optimizer (PSO) and GWO algorithms, the experimental results showed that the DE-OTSU-GWO algorithm is more stable and accurate in solving functions. In addition, compared with other algorithms, a convergence behavior analysis proved the high quality of the DE-OTSU-GWO algorithm. In the results of classical agricultural image recognition problems, compared with GWO, PSO, DE-GWO, and 2D-OTSU-FA, the DE-OTSU-GWO algorithm had accuracy in straw image recognition and is applicable to practical problems. The OTSU algorithm improves the accuracy of the overall algorithm while increasing the running time. After adding the DE algorithm, the time complexity will increase, but the solution time can be shortened. Compared with GWO, DE-GWO, PSO, and 2D-OTSU-FA, the DE-OTSU-GWO algorithm has better results in segmentation assessment.

Effect of body configuration at step contact on balance recovery from sideways perturbations

Compensatory stepping is an important protective mechanism to prevent falling. To recover from sideways perturbations side steps are generally more advantageous than cross-over steps. However, there is lack of understanding of the characteristics of compensatory side steps following sideways perturbations that separate successful recoveries (i.e., no falls) from falls, the most clinically relevant outcome following a balance perturbation. We aimed to identify the critical determinants for successful side stepping after large sideways balance perturbations. Twelve healthy young adults were subjected to large leftward perturbations at varying intensities on a translating sheet. For recovery attempts started with a side step, we determined body configuration variables (frontal-plane leg and trunk angle) at first step contact, as well as spatiotemporal step variables (onset, length, duration, velocity). A logistic regression analysis was conducted to determine the predictive ability of body configuration and spatiotemporal variables on the probability of success (no fall vs. fall); perturbation intensity (peak jerk of translating sheet) and a random effect for individual were also included in the model. In the final model, leg angle and peak jerk were retained as predictors of successful balance recovery and these variables correctly classified the recovery outcome in 86% of the trials. This final ‘body configuration’ model yielded a −2 log likelihood of −36.3, whereas the best fitting model with only spatiotemporal variables yielded a −2 log likelihood of −45.8 (indicating a poorer fit). The leg angle at a given perturbation intensity appears to be a valid measure of reactive side step quality. The relative ease of measuring this leg angle at step contact makes it a candidate outcome for reactive stepping assessments in clinical practice.

Perturbation-evoked lateral steps in older adults: Why take two steps when one will do?

BackgroundHip fractures in older adults often result from a fall in the lateral direction. While younger adults tend to recover balance from a lateral perturbation with a single lateral sidestep, older adults are prone to multistep responses which are associated with an increased fall risk. This study compared the stepping characteristics and stability of single and multistep responses to lateral perturbation in healthy older adults. MethodsEighty-four older adults received lateral waist-pull perturbations to either side. Spatio-temporal stepping characteristics and balance stability were quantified. FindingsFewer steps were taken to recover balance when the first step was a lateral sidestep. The stability margin of single lateral sidesteps was greater than medial sidesteps and cross-over steps to the back but not significantly different from single cross-over steps to the front at step termination. Single step responses were more stable than multistep responses at step termination and at step initiation for lateral sidesteps and cross-over steps to the front. The decreased stability of multistep responses was attributed to an increased center of mass velocity and a smaller distance between the center of mass and base-of-support at step termination. InterpretationAlthough lateral sidesteps result in fewer steps than cross-over steps to the front, the stability margin was not significantly different at step termination. These results suggest difficulty terminating center of mass motion and/or inefficient center of mass control differentiates single and multistep responses. Future studies should investigate perturbation training and/or hip abductor muscle conditioning as a means of improving compensatory stepping reactions.

Turning Stability in Individuals With Parkinson Disease.

Although instability during turning is a disabling feature of Parkinson disease (PD), little is known about the associated postural characteristics. Our goals were to compare turning stability between individuals with PD and healthy individuals and to investigate whether dopaminergic medication improves turning stability. Nineteen older adults with mild to moderate PD and 19 healthy individuals walked straight or walked and turned 180° to the right or left. The turning direction was visually cued before (preplanned) or during (unplanned) straight walking. Participants with PD were assessed off and on medication. As a proxy for mediolateral stability, we calculated the difference between pelvis lateral displacement and the lateral edge of the support base. While healthy individuals regulated mediolateral stability in a steady-state manner during turning, mediolateral stability in PD was reduced for crossover steps (narrow steps by the foot contralateral to the turning direction) and increased for side steps (widening steps by the foot ipsilateral to the turning direction) (P ≤ 0.008). Individuals with PD turned with narrower step width (P ≤ 0.024) and smaller pelvis displacement than healthy individuals (P ≤ 0.002). Dopaminergic medication only improved mediolateral stability while using side steps to initiate unplanned turns (P < 0.001). Turning stability was compromised in PD, but only for crossover steps with a narrow support base. As dopaminergic medication showed limited effect on turning stability, rehabilitation plays an important role to promote safe turning strategies with a specific emphasis on sustainment of a wide support base.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A236).

Characterization of Reactions to Laterally Directed Perturbations in People With Chronic Stroke.

Reactive balance control is often impaired poststroke. Studies addressing responses to laterally directed perturbations in this population are currently lacking. Given that stroke-related motor impairments are unilateral, a better understanding of reactive balance responses to these types of perturbations is critical. This study aimed to quantify differences in reactive balance control in response to laterally directed perturbations in people with chronic stroke, based on perturbation direction and ability to step with either limb. This study used a cross-sectional design. Participants with chronic stroke (N=19) were divided into groups representing their ability to step with either limb, based on performance on a reactive balance task in a baseline assessment. The preferred stepping limb was also identified during this assessment. Each participant then underwent a series of laterally directed perturbations on a motion platform. Behavioral measures were compared between platform direction and group. Trials with extra steps, step initiation with the preferred limb, and crossover steps were more common with platform motion toward the preferred limb compared to the nonpreferred limb; the latter effect was only observed for participants with an impaired ability to step with either limb. Side-step sequences were more common in those able to step with either limb when the platform moved toward the preferred limb. The participant sample was likely higher functioning than the general population of stroke survivors due to equipment constraints. Additionally, participants may have developed strategies to use the platform's motion characteristics to aid with balance recovery. These findings provide an indication of responses to laterally directed perturbations in people with chronic stroke and may help inform strategies for improving reactive balance control during stroke rehabilitation.

EGA-FMC: enhanced genetic algorithm-based fuzzy k-modes clustering for categorical data

Categorical data clustering is the unsupervised technique of grouping similar objects which have categorical attributes. We propose a genetic algorithm-based fuzzy k-modes categorical data clustering algorithm using multi-objective rank-based selection with enhanced elitism operation. Compactness of the clusters and inter-cluster separation were chosen as objectives to be optimised. During elitism, in every iteration, the best parent chromosomes were identified. The entire population was passed through the selection, crossover and mutation steps. The worst children were then replaced by the best parents. Our method was evaluated on three real-world datasets and resulted in clusters of better quality as compared to current methods with a significant reduction in computation time. Additionally, statistical significance tests were conducted to show the superiority of our approach over other clustering solutions.

The Next Step in Understanding Impaired Reactive Balance Control in People With Stroke: The Role of Defective Early Automatic Postural Responses

Background and objective. Postural muscle responses are often impaired after stroke. We aimed to identify the contribution of deficits in very early postural responses to poorer reactive balance capacity, with a particular focus on reactive stepping as a key strategy for avoiding falls. Methods. A total of 34 chronic stroke survivors and 17 controls were subjected to translational balance perturbations in 4 directions. We identified the highest perturbation intensity that could be recovered without stepping (single stepping threshold [SST]) and with maximally 1 step (multiple stepping threshold [MST]). We determined onset latencies and response amplitudes of 7 leg muscles bilaterally and identified associations with balance capacity. Results. People with stroke had a lower MST than controls in all directions. Side steps resulted in a higher lateral MST than crossover steps but were less common toward the paretic side. Postural responses were delayed and smaller in amplitude on the paretic side only. We observed the strongest associations between gluteus medius (GLUT) onset and amplitude and MST toward the paretic side (R2 = 0.33). Electromyographic variables were rather weakly associated with forward and backward MSTs (R2 = 0.10-0.22) and with SSTs (R2 = 0.08-0.15). Conclusions. Delayed and reduced paretic postural responses are associated with impaired reactive stepping after stroke. Particularly, fast and vigorous activity of the GLUT is imperative for overcoming large sideways perturbations, presumably because it facilitates the effective use of side steps. Because people with stroke often fall toward the paretic side, this finding indicates an important target for training.

유전 알고리즘을 이용한 플레이어 적응형 몬스터 생성 기법

게임 산업이 발전하면서 콘텐츠의 생성 속도보다 훨씬 빠른 속도로 콘텐츠가 소비되고 있고, 플레이어의 게임 숙련도에 적합한 레벨의 게임 콘텐츠들이 지속적으로 제공될 것을 필요로 하고 있다. 이러한 문제를 효과적으로 해결하기 위해 활용되는 방법이 인공지능(Artificial Intelligence, AI)을 이용한 절차적 콘텐츠 생성(Procedural Content Generation, PCG)이다. 본 논문에서는 유전 알고리즘을 이용하여 플레이어에게 적합한 난이도를 가지고 있는 다양한 종류의 몬스터를 자동 생성하는 절차적 방법을 제안한다. 몬스터들의 주요 속성을 유전자로 구성하고 다양한 종류의 몬스터 유전자들로 염색체를 만들어 이용한다. 생성된 몬스터와 플레이어의 전투 시뮬레이션으로 유전자를 평가하여 선택 후 교배한다. 본 논문의 제안 방법을 이용해 플레이어 적응형 몬스터들을 유전 알고리즘에 기반을 두어 절차적으로 생성하고, 염색체 개수에 따라 생성된 몬스터의 다양성을 비교해본다. As the game industry is blooming, the generation of contents is far behind the consumption of contents. With this reason, it is necessary to afford the game contents considering level of game player's skill. In order to effectively solve this problem, Procedural Content Generation(PCG) using Artificial Intelligence(AI) is one of the plausible options. This paper proposes the procedural method to generate various monsters considering level of player's skill using genetic algorithm. One gene consists of the properties of a monster and one genome consists of genes for various monsters. A generated monster is evaluated by battle simulation with a player and then goes through selection and crossover steps. Using our proposed scheme, players adaptive monsters are generated procedurally based on genetic algorithm and the variety of monsters which are generated with different number of genome is compared.

Pre- and unplanned walking turns in Parkinson’s disease – Effects of dopaminergic medication

Although dopaminergic medication improves functional mobility in individuals with Parkinson’s disease (PD), its effects on walking turns are uncertain. Our goals was to determine whether dopaminergic medication improves preplanned and unplanned walking turns in individuals with PD, compared to healthy controls. Nineteen older adults with mild-to-moderate PD and 17 healthy controls performed one of the following three tasks, presented randomly: walking straight, or walking and turning 180° to the right or left. The walking direction was visually cued before starting to walk (preplanned) or after (unplanned, i.e., 0.6m before reaching the turning point). Subjects with PD were assessed off dopaminergic medication (OFF) and on dopaminergic medication (ON) medication. Turning strategy (step and spin turns), turning performance (turning distance and body rotation) and walking pattern were analyzed for three turning steps. Irrespective of medication state and turning condition, step and spin turns followed a nearly 50:50 distribution. After intake of dopaminergic medication, subjects with PD increased their turning distance but not the amount of body rotation or their walking pattern. Compared to controls, turning impairments in subjects with PD remained while ON medication and problems regulating step width were the most prominent features of their walking pattern. Specifically, subjects with PD turned with narrower cross-over steps, i.e. when the external foot crossed over the line of progression of the internal leg. We conclude that turning impairments remained even after dopaminergic medication and problems modulating step width appears to be a critical feature for turning in PD.

An improved Genetic Algorithm for spatial optimization of multi-objective and multi-site land use allocation

As a result of multiple land use types, spatial heterogeneity, and conflicts of interest among multiple participants, multi-site land use allocation becomes a complex and significant optimization issue. We propose an improved Genetic Algorithm (GA) to deal with multi-site land use allocation, in which maximum economic benefit, maximum ecological benefit, maximum suitability, and maximum compactness were formulated as optimal objectives; and residential space demand and some regulatory knowledge were set as constraints. A Goal Programming model with a reference point form was used to manage trade-offs among multiple objectives. In order to improve the efficiency of the common GA applied to multi-site land use allocation, two crossover steps and two mutation operations were designed. This paper presents an application of the improved GA to the Regional District of Central Okanagan in Canada. Results showed that the proposed GA exhibited good robustness and could generate any optimal land use scenario according to stakeholders' preferred objectives, thus having the potential to provide interactive technical support for land use planning.

Using gait parameters to detect fatigue and responses to ice slurry during prolonged load carriage

This study examined (1) if changes in gait characteristics could indicate the exertional heat stress experienced during prolonged load carriage, and (2) if gait characteristics were responsive to a heat mitigation strategy. In an environmental chamber replicating tropical climatic conditions (ambient temperature 32°C, 70% relative humidity), 16 males aged 21.8 (1.2) years performed two trials of a work-rest cycle protocol consisting two bouts of 4-km treadmill walks with 30-kg load at 5.3km/h separated by a 15-min rest period. Ice slurry (ICE) or room temperature water (29°C) as a control (CON) was provided in 200-ml aliquots. The fluids were given 10min before the start, at the 15th and 30th min of each work cycle, and during each rest period. Spatio-temporal gait characteristics were obtained at the start and end of each work-rest cycle using a floor-based photocell system (OptoGait) and a high-speed video camera at 120Hz. Repeated-measure analysis of variance (trial×time) showed that with time, step width decreased (p=.024) while percent crossover steps increased (p=.008) from the 40th min onwards. Reduced stance time variability (−11.1%, p=.029) step width variability (−8.2%, p=.001), and percent crossover step (−18.5%, p=.010) were observed in ICE compared with CON. No differences in step length and most temporal variables were found. In conclusion, changes in frontal plane gait characteristics may indicate exertional heat stress during prolonged load carriage, and some of these changes may be mitigated with ice slurry ingestion.

Correlation between midline gait function performance and verbal fluency in patients with Parkinson's disease.

Verbal fluency impairments are among the earliest and most common cognitive deficits in Parkinson's disease (PD), yet more than one study has shown that as a group, verbal fluency performance is not always different between patients with PD and age-matched controls. Here we examined whether PD-related deficits in speech and language capabilities are detectable in patients who exhibit poor midline motor function, such as control of gait. We postulated that if phonemic verbal fluency (PVF) performance in PD is dissociable from other factors such as age in this patient subgroup, a low PVF will likely reflect a general cognitive-motor deficit attributable to Parkinsonian pathology. Thirty-one PD and thirteen controls were evaluated on PVF and the Metronome-Paced Square Step Test (MPSST), a complex sensorimotor task that challenges axial and midline function. The MPSST requires a patient to initiate and maintain a consecutive series of diagonal and midline cross-over steps during the test. We found that despite similar PVF performance between groups, the vast majority of controls but not patients completed the MPSST without any errors, and the odds of completing the MPSST without any errors was 15 times greater among control. More importantly, a significant amount of PVF variability was explained by MPSST performance in PD but not controls even after controlling for age and disease duration. Together, these results provide evidence that PVF performance in PD likely reflects a PD-specific process and suggests that the MPSST may be a more sensitive test of PD-specific pathology than PVF.

Center of pressure control for balance maintenance during lateral waist-pull perturbations in older adults

When balance is disturbed, location of the center of pressure (COP) contributes to a person’s ability to recover from a perturbation. This study investigated COP control prior to first step lift-off (FSLO) during lateral perturbations in older non-fallers and fallers. 38 non-fallers and 16 fallers received lateral waist-pulls at 5 different intensities. Crossover stepping responses at the intensity level where the largest number of subjects responded with crossover steps were analyzed. Whole-body center of mass (COM) and COP positions in the medio-lateral (ML) direction with respect to the base of support (BOS), and COP velocity were calculated. An inverted pendulum model was used to define the BOS stability boundary at FSLO, which was also adjusted using the COP position at FSLO (functional boundary). No significant differences were found in the COP velocities between fallers and non-fallers (p>.093). However, the COP positions for fallers were located significantly more medial at FSLO (p≤.01), resulting in a significantly reduced functional boundary. Although the stability margins, measures of stability based on the BOS, were significantly larger than zero for fallers (p≤.004), they were not significantly different from zero for the functional boundary, i.e., reaching the functional stability limit. Fallers had reduced functional limits of stability in the ML direction, which would predispose them to more precarious stability conditions than non-fallers. This could be a cause for taking more steps than non-fallers for balance recovery as we observed. The functional boundary estimation may be a more sensitive marker of balance instability than the BOS boundary.

Leg preference associated with protective stepping responses in older adults

BackgroundAsymmetries in dynamic balance stability have been previously observed. The goal of this study was to determine whether leg preference influenced the stepping response to a waist-pull perturbation in older adult fallers and non-fallers. Methods39 healthy, community-dwelling, older adult (>65years) volunteers participated. Participants were grouped into non-faller and faller cohorts based on fall history in the 12months prior to the study. Participants received 60 lateral waist-pull perturbations of varying magnitude towards their preferred and non-preferred sides during quiet standing. Outcome measures included balance tolerance limit, number of recovery steps taken and type of recovery step taken for perturbations to each side. FindingsNo significant differences in balance tolerance limit (P≥0.102) or number of recovery steps taken (η2partial≤0.027; P≥0.442) were observed between perturbations towards the preferred and non-preferred legs. However, non-faller participants more frequently responded with a medial step when pulled towards their non-preferred side and cross-over steps when pulled towards their preferred side (P=0.015). InterpretationLeg preference may influence the protective stepping response to standing balance perturbations in older adults at risk for falls, particularly with the type of recovery responses used. Such asymmetries in balance stability recovery may represent a contributing factor for falls among older individuals and should be considered for rehabilitation interventions aimed at improving balance stability and reducing fall risk.