Stance Tasks Research Articles

Temporal more than spatial regulation of sway is important for posture in response to an ultra-compliant surface

Background and aim: Many people use balance training as a rehabilitation or habilitation modality. Although the time course of changes to temporal and spatial aspects of postural sway over the initial weeks of such training is as yet unclear. Particularly, we sought to explore the effects of training on sway during a dynamic task of stance on an ultra-compliant surface. Such a task provides different mechanical, and thus sensorimotor, constraints compared to stance on a solid surface.Methods: Center of pressure (COP) was measured on an ultra-compliant surface atop a force plate at the start of each of 18 days of a 6-week balance training program. Range and standard deviation quantified amount of sway while velocity and Lyapunov exponent (LyE) quantify speed and rhythmicity of sway, respectively.Results: Trend analysis indicated quadratic changes in COP range and standard deviation, with initial reductions followed by returns to initial values by the end of training. Linear reduction of movement velocity and LyE continued through the duration of the program. Reduced LyE indicates regular (self-similar) structure of the COP path.Conclusions: These results provide insight to the developing postural strategy necessary for maintaining upright stance within the dynamics created by interactions with an ultra-compliant surface. Participants showed sensitivity to surface properties, moving both more slowly and with a more regular movement pattern; suggesting that they were able to develop a more feed-forward approach to the maintenance of balance by exploiting task constraints.

Use of a Dynamic Balance System to Quantify Postural Steadiness and Stability of Individuals with Lower-Limb Amputation: A Pilot Study

ABSTRACT Introduction Despite rehabilitation and gait training, the gait of individuals with lower-limb amputation is often asymmetric and falls and/or fear of falling are common. Clinical assessments of balance and stability include the Berg Balance Scale and the Dynamic Gait Index. Biomechanical assessments, conducted largely in research laboratories, are more objective, quantitative, and may provide greater resolution. These biomechanical measures include postural sway during both unilateral and bilateral standing tasks and the dynamic postural response to applied or volitional perturbations. The objective of this study was to investigate the utility of a dynamic balance system, a relatively new clinical tool incorporating dual force plates similar to that used in research laboratories, to assess the postural steadiness and stability of a small, diverse population of persons with lower-limb amputation. The specific aim was to investigate whether differences in balance of persons with amputation due to changes in prosthetic componentry were reflected in the resultant data. Materials and Methods Dynamic balance testing was conducted using the Bertec Balance Advantage–Dynamic CDP system on five adult subjects with varying levels of lower-limb amputation. Trials were conducted in both the subjects' current prosthesis and alternative prosthetic componentry after a 1-week acclimation period. Specific tasks included limits of stability, weight-bearing squats, and unilateral stance. Results Subjects had difficulty shifting their weight during the limits of stability task; both the maximum excursion and anteroposterior directional control varied with prosthetic componentry. Load sharing also varied with prosthetic componentry. Load sharing became more asymmetric as knee flexion increased during the weight-bearing bilateral squat tasks, with less weight supported on the prosthetic limb. Finally, the metrics for the unilateral stance task varied with prosthetic componentry. Conclusions The dynamic balance system tasks and related metrics demonstrated the potential to discern differences in balance in persons with amputation due to changes in prosthetic componentry. Further study is needed to investigate these parameters, their correlation with clinical measures of balance, and the effects of both prosthetic componentry and alignment.

Destabilization of the Upright Posture Through Elevation of the Center of Mass.

The inverted pendulum model predicts that the major challenge for neural control of the upright posture is the inherent instability of the body due to the center of mass (COM) being above the base of support (BOS). If so, even slight elevation of the COM may substantially destabilize posture. The destabilizing effect of heavy load positioned above the COM has been demonstrated. We examined sensitivity of posture to light (1-5% of body weight) load by placing weights on the shoulders and assessing functional reach distance in the forward, right, and left directions and postural sway during quiet stance. At each load level, the quiet stance task was tested with and without vision. The 1% of body weight load significantly shortened reach distance in the forward direction. It also increased postural sway. Interestingly, additional weight did not result in further deficits. The results support high sensitivity of postural stability to COM elevation that increases the challenge for neural control of posture and that can potentially be used for early detection of declines in postural stability.

3-Hz postural tremor in multiple system atrophy cerebellar type (MSA-C)-a static posturography study.

The objective of the study is to evaluate postural dysfunction of multiple system atrophy-parkinsonian type (MSA-P) and cerebellar type (MSA-C) by static posturography exam. A total of 29 MSA-P patients, 40 MSA-C patients, and 23 healthy controls (HC) were recruited and engaged in a sensory organization test (SOT). The amplitude of the postural sway was measured and transformed into energy value by Fourier analyzer. SOT scores, frequency of fallsand typical 3-Hz postural tremors during the four stance tasks, and energy value in three different frequency bands were recorded and compared. Compared with HC, SOT scores were significantly lower in MSA groups (P<0.01). Compared with MSA-P, the vestibular scores were further reduced in MSA-C patients (P<0.05). Falls were more frequent in MSA groups, especially in SOT4 task (foam surface with eyes closed) or in MSA-C group (P<0.05). Typical 3-Hz postural tremor was observed in 97.5% MSA-C patients, in 24.1% MSA-P patients but in none of the HC (P<0.05). Compared with HC, much more energy was consumed in every task, every direction, and nearly every frequency band in MSA groups. Energy value of MSA-C group was significantly higher than that of MSA-P, especially in higher frequency band (2~20Hz) or in more difficult stance tasks (SOT 3~4, foam surface with eyes open or closed) (P<0.05). Both MSA-P and MSA-C were characterized by severe static postural dysfunction. However, typical 3-Hz postural tremor was predominant in MSA-C and was very useful in the differential diagnosis between MSA-P and MSA-C.

Sport Skill–Specific Expertise Biases Sensory Integration for Spatial Referencing and Postural Control

ABSTRACTThe authors asked how sport expertise modulates visual field dependence and sensory reweighting for controlling posture. Experienced soccer athletes, ballet dancers, and nonathletes performed (a) a Rod and Frame test and (b) a 100-s bipedal stance task during which vision and proprioception were successively or concurrently disrupted in 20-s blocks. Postural adaptation was assessed in the mean center of pressure displacement, root mean square of center of pressure velocity and ankle muscles integrated electromyography activity. Soccer athletes were more field dependent than were nonathletes. During standing, dancers were more destabilized by vibration and required more time to reweigh sensory information compared with the other 2 groups. These findings reveal a sport skill–specific bias in the reweighing of sensory inputs for spatial orientation and postural control.

Multi-level Analysis of Distracted Drivers’ Glances: Enhancing the Robustness of the NHTSA Acceptance Criteria

The visual-manual distraction guidelines by National Highway Traffic Safety Administration (NHTSA) provide a method to assess potential distraction of secondary tasks. According to the method, one instance of “testable task” is performed once by 24 participants, and three glance measures (i.e., mean duration of off-road glances, total eyes off road time, and proportion of long glances) are used to decide whether the task imposes acceptable demand on the driver. The current study investigates variability from both participants and task instances (e.g., different telephone numbers used for dialing telephone number task) reflected in these glance measures, with repeated sampling of participants and repeated sampling of task instances. While NHTSA test method is vulnerable to both sources of variability, multi-level statistical modeling and sampling task instances offers a promising approach to overcome this limitation.

Reliability-aware low energy scheduling in real time systems with shared resources

Dynamic voltage scaling (DVS) is a technique which is widely used to save energy in a real time system. Recent research shows that it has a negative impact on the system reliability. In this paper, we consider the problem of the system reliability and focus on a periodic task set that the task instance shares resources. Firstly, we present a static low power scheduling algorithm for periodic tasks with shared resources called SLPSR which ignores the system reliability. Secondly, we prove that the problem of the reliability-aware low power scheduling for periodic tasks with shared resources is NP-hard and present two heuristic algorithms called SPF and LPF respectively. Finally, we present a dynamic low power scheduling algorithm for periodic tasks with shared resources called DLPSR to reclaim the dynamic slack time to save energy while preserving the system reliability. Experimental results show that the presented algorithm can reduce the energy consumption while improving the system reliability.

The influence of vibratory stimulus using stochastic resonance on static posture control ability of senior adults

Purpose The purpose of the study was to investigate the effect of vibratory stimulus on the static postural control of 8 healty senior adults. Methods To achieve this goal, all subjects participated in two different kinds of static postural control tasks. Task 1 was a static postural control task, where both-legs stand on the ground. Second task was an unstable static postural control task using only single leg stance. As they maintain their balance, 6 different vibratory stimulus were provided on the sole of their feet(personal threshold 0%, 80%, 90%, 100%, 110%, 120%). Results The results of the study were as follows: First, there was no significant differences in postural control ability according to different types of vibrator intensity. Second, there was a significant difference in single-leg postural control ability according to vibrator intensity. Third, there was a significant difference in anterio-posterior stability according to the different types of vibrator intensity. Conclusion Stochastic resonance using vibratory stimulus was more effective in the single leg stance task, rather than the double leg stance task. Moreover, sub-threshold vibratory stimulus(80%, 90%) intensity were more effective than higher vibratory stimulus(100%, 110%, 120%).

On the Heterogeneity Bias of Cost Matrices for Assessing Scheduling Algorithms

Assessing the performance of scheduling heuristics through simulation requires one to generate synthetic instances of tasks and machines with well-identified properties. Carefully controlling these properties is mandatory to avoid any bias. We consider the scheduling problem consisting of allocating independent sequential tasks on unrelated machines while minimizing the maximum execution time. In this problem, the instance is a cost matrix that specifies the execution cost of any task on any machine. This article proposes two measures for quantifying the heterogeneity properties of a cost matrix. An analysis of two classical methods used in the literature reveals a bias in previous studies. We propose new methods to generate instances with given heterogeneity properties and we show that heterogeneity has a significant impact on twelve heuristics.

Schedule construction under precedence constraints in flexray in-vehicle networks

As embedded time-triggered applications have widely replaced mechanical systems in modern automobiles, holistic scheduling of tasks and messages of such applications on in-vehicle networks has become a critical issue. For offering QoS (Quality of Service) guarantees, the holistic schedule must satisfy numerous constraints such as protocol specifications, delay constraints and precedence constraints between tasks schedules and messages transmissions. Existing approaches to this problem search through a vast design space of all possible joint task and message schedules. This leads to a high complexity and limits the scalability of such approaches for scheduling the large scale systems. To cope with this problem, we propose an approach that divides the holistic scheduling problem to two sub-problems: the sub-problem of message scheduling and the sub-problem of task scheduling, while precedence relations and end-to-end information passing between task instances and messages are preserved and the end-to-end deadlines are guaranteed. This helps to reduce the workload on the problem solvers and improves efficiency and scalability. In the first sub-problem, our approach optimizes scheduling the set of messages and allocates time windows for scheduling each task with respect to precedence constraints, end-to-end deadlines and FlexRay protocol specifications. The length of each time window helps to preserve the respective tasks schedulability and to provide flexibility for both task and message scheduling. The objective is defined with respect to extensibility issues. In the second sub-problem, our approach optimizes schedule of the set of tasks with respect to their allocated time windows and timing constraints. The objective is defined with respect to latency issues. We optimize the solution to each sub-problem using Mixed Integer Linear Programming optimization framework. Performance evaluations show that, compared with existing holistic scheduling approaches, our approach is more scalable and obtains better solutions in a reasonable amount of time.

Selection of trajectory parameters for dynamic pouring tasks based on exploitation-driven updates of local metamodels

SUMMARYWe present an approach that allows a robot to generate trajectories to perform a set of instances of a task using few physical trials. Specifically, we address manipulation tasks which are highly challenging to simulate due to complex dynamics. Our approach allows a robot to create a model from initial exploratory experiments and subsequently improve it to find trajectory parameters to successfully perform a given task instance. First, in a model generation phase, local models are constructed in the vicinity of previously conducted experiments that explain both task function behavior and estimated divergence of the generated model from the true model when moving within the neighborhood of each experiment. Second, in an exploitation-driven updating phase, these generated models are used to guide parameter selection given a desired task outcome and the models are updated based on the actual outcome of the task execution. The local models are built within adaptively chosen neighborhoods, thereby allowing the algorithm to capture arbitrarily complex function landscapes. We first validate our approach by testing it on a synthetic non-linear function approximation problem, where we also analyze the benefit of the core approach features. We then show results with a physical robot performing a dynamic fluid pouring task. Real robot results reveal that the correct pouring parameters for a new pour volume can be learned quite rapidly, with a limited number of exploratory experiments.

The role of sensory augmentation for people with vestibular deficits: Real-time balance aid and/or rehabilitation device?

This narrative review highlights findings from the sensory augmentation field for people with vestibular deficits and addresses the outstanding questions that are critical to the translation of this technology into clinical and/or personal use. Prior research has demonstrated that the real-time use of visual, vibrotactile, auditory, and multimodal sensory augmentation technologies can improve balance during static and dynamic stance tasks within a laboratory setting. However, its application in improving gait requires additional investigation, as does its efficacy as a rehabilitation device for people with vestibular deficits. In some locomotor studies involving sensory augmentation, gait velocity decreased and secondary task performance worsened, and subjects negatively altered their segmental control strategies when cues were provided following short training sessions. A further question is whether the retention and/or carry-over effects of training with a sensory augmentation technology exceed the retention and/or carry-over effects of training alone, thereby supporting its use as a rehabilitation device. Preliminary results suggest that there are short-term improvements in balance performance following a small number of training sessions with a sensory augmentation device. Long-term clinical and home-based controlled training studies are needed. It is hypothesized that sensory augmentation provides people with vestibular deficits with additional sensory input to promote central compensation during a specific exercise/activity; however, research is needed to substantiate this theory. Major obstacles standing in the way of its use for these critical applications include determining exercise/activity specific feedback parameters and dosage strategies. This paper summarizes the reported findings that support sensory augmentation as a balance aid and rehabilitation device, but does not critically examine efficacy or the quality of the research methods used in the reviewed studies.

People with chronic low back pain have poorer balance than controls in challenging tasks

Purpose: To compare the balance of individuals with and without chronic low back pain during five tasks.Method: The participants were 20 volunteers, 10 with and 10 without nonspecific chronic low back pain, mean age 34 years, 50% females. The participants completed the following balance tasks on a force platform in random order: (1) two-legged stance with eyes open, (2) two-legged stance with eyes closed, (3) semi-tandem with eyes open, (4) semi-tandem with eyes closed and (5) one-legged stance with eyes open. The participants completed three 60-s trials of tasks 1–4, and three 30-s trials of task 5 with 30-s rests between trials. The center of pressure area, velocity and frequency in the antero-posterior and medio-lateral directions were computed during each task, and compared between groups and tasks.Results: Participants with chronic low back pain presented significantly larger center of pressure area and higher velocity than the healthy controls (p < 0.001). There were significant differences among tasks for all center of pressure variables (p < 0.001). Semi-tandem (tasks 3 and 4) and one-leg stance (task 5) were more sensitive to identify balance impairments in the chronic low back pain group than two-legged stance tasks 1 and 2 (effect size >1.37 vs. effect size <0.64). There were no significant interactions between groups and tasks.Conclusions: Individuals with chronic low back pain presented poorer postural control using center of pressure measurements than the healthy controls, mainly during more challenging balance tasks such as semi-tandem and one-legged stance conditions.Implications for RehabilitationPeople with chronic low back had poorer balance than those without it.Balance tasks need to be sensitive to capture impairments.Balance assessments during semi-tandem and one-legged stance were the most sensitive tasks to determine postural control deficit in people with chronic low back.Balance assessment should be included during rehabilitation programs for individuals with chronic low back pain for better clinical decision making related to balance re-training as necessary.

Worst-Case Response Time Analysis of a Synchronous Dataflow Graph in a Multiprocessor System with Real-Time Tasks

In this article, we propose a novel technique that estimates a tight upper bound of the worst-case response time (WCRT) of a synchronous dataflow (SDF) graph when the SDF graph shares processors with other real-time tasks. When an SDF graph is executed at runtime under a self-timed or static assignment scheduling policy on a multi-processor system, static scheduling of the SDF graph does not guarantee the satisfaction of latency constraints since changes to the schedule may result in timing anomalies. To estimate the WCRT of an SDF graph with a given mapping and scheduling result, we first construct a task instance dependency graph that depicts the dependency between node executions in a static schedule. The proposed technique combines two techniques in a novel way: schedule time bound analysis and response time analysis. The former is used to consider the interference between task instances in the same SDF graph, and the latter is used to consider the interference from other real-time tasks. Through extensive experiments with synthetic examples and benchmarks, we verify the superior performance of the proposed technique compared to other existent techniques.

The Coherence between Fear of Falling and Dynamic Postural Capability

Objectives: In the context of fear of falling (FoF) and fall-related self-efficacy have a significant impact on the functional performance in gait mobility, postural function and activities of daily living. In this study, we analysed the relation between FoF with the 7-item version Fall Efficacy Scale-International (short FES-I) and biomechanical measurements of balance. Methods: 25 geriatric patients with increased short FES-I Score (18.5 CI 14.0-24.1; Cut-off ≥ 10/28 points) carried out fourteen different stance and gait tasks to objective the complex postural capability (Sway StarTM System Specific Body Control Index (BCI) compared trunk sway (°, °/s) and time to go with an age and sex matched control group. Correlation between short FES-I and biomechanical parameters were calculated Results: Increased short FES-I score do not correlate with BCI and major single tasks trunk sway parameters (° and °/s), but correlate significantly positive with time to go tasks. Discussion: FoF and lower fall self-efficacy does not necessarily lead to a higher postural instability. However, gait was reduced in speed but not necessarily instable (i.e. increased trunk sway amplitudes). Increasing data in diagnostic procedures will cause more complex recommendations in therapeutic strategies.

A Domain Specific Approach to High Performance Heterogeneous Computing

Users of heterogeneous computing systems face two problems: first, in understanding the trade-off relationships between the observable characteristics of their applications, such as latency and quality of the result, and second, how to exploit knowledge of these characteristics to allocate work to distributed computing platforms efficiently. A domain specific approach addresses both of these problems. By considering a subset of operations or functions, models of the observable characteristics or domain metrics may be formulated in advance, and populated at run-time for task instances. These metric models can then be used to express the allocation of work as a constrained integer program. These claims are illustrated using the domain of derivatives pricing in computational finance, with the domain metrics of workload latency and pricing accuracy. For a large, varied workload of 128 Black-Scholes and Heston model-based option pricing tasks, running upon a diverse array of 16 Multicore CPUs, GPUs and FPGAs platforms, predictions made by models of both the makespan and accuracy are generally within 10 percent of the run-time performance. When these models are used as inputs to machine learning and MILP-based workload allocation approaches, a latency improvement of up to 24 and 270 times over the heuristic approach is seen.

The Stationary-Gaze Task Should Not Be Systematically Used as the Control Task in Studies of Postural Control

ABSTRACTIn studies of postural control, a control task is often used to understand significant effects obtained with experimental manipulations. This task should be the easiest task and (therefore) engage the lowest behavioral variability and cognitive workload. Since 1983, the stationary-gaze task is considered as the most relevant control task. Instead, the authors expected that free looking at small targets (white paper or images; visual angle: 12°) could be an easier task. To verify this assumption, 16 young individuals performed stationary-gaze, white-panel, and free-viewing 12° tasks in steady and relaxed stances. The stationary-gaze task led to significantly higher cognitive workload (mean score in the National Aeronotics and Space Administration Task Load Index questionnaire), higher interindividual body (head, neck, and lower back) linear variability, and higher interindividual body angular variability—not systematically yet—than both other tasks. There was more cognitive workload in steady than relaxed stances. The authors also tested if a free-viewing 24° task could lead to greater angular displacement, and hence greater body sway, than could the other tasks in relaxed stance. Unexpectedly, the participants mostly moved their eyes and not their body in this task. In the discussion, the authors explain why the stationary-gaze task may not be an ideal control task and how to choose this neutral task.

Noisy galvanic vestibular stimulation induces a sustained improvement in body balance in elderly adults.

Vestibular dysfunction causes postural instability, which is prevalent in the elderly. We previously showed that an imperceptible level of noisy galvanic vestibular stimulation (nGVS) can improve postural stability in patients with bilateral vestibulopathy during the stimulus, presumably by enhancing vestibular information processing. In this study, we investigated the after-effects of an imperceptible long-duration nGVS on body balance in elderly adults. Thirty elderly participants underwent two nGVS sessions in a randomised order. In Session 1, participants received nGVS for 30 min twice with a 4-h interval. In Session 2, participants received nGVS for 3 h. Two-legged stance tasks were performed with eyes closed while participants stood on a foam rubber surface, with and without nGVS, and parameters related to postural stability were measured using posturography. In both sessions, the postural stability was markedly improved for more than 2 h after the cessation of the stimulus and tended to decrease thereafter. The second stimulation in Session 1 caused a moderate additional improvement in body balance and promoted the sustainability of the improvement. These results suggest that nGVS can lead to a postural stability improvement in elderly adults that lasts for several hours after the cessation of the stimulus, probably via vestibular neuroplasticity.

Concurrent Task Scheduling and Dynamic Voltage and Frequency Scaling in a Real-Time Embedded System With Energy Harvesting

Energy harvesting is a promising technique to overcome the limit on energy availability and increase the lifespan of battery-powered embedded systems. In this paper, the question of how one can achieve the prolonged lifespan 1 of a real-time embedded system with energy harvesting capability (RTES-EH) is investigated. The RTES-EH comprises a photovoltaic (PV) panel for energy harvesting, a supercapacitor for energy storage, and a real-time sensor node as the embedded load device. A global controller performs simultaneous optimal operating point tracking for the PV panel, state-of-charge (SoC) management for the supercapacitor, and energy-harvesting-aware real-time task scheduling with dynamic voltage and frequency scaling (DVFS) for the sensor node, while employing a precise solar irradiance prediction method. The controller employs a cascaded feedback control structure, where an outer supervisory control loop performs real-time task scheduling with DVFS in the sensor node while maintaining the optimal supercapacitor SoC for improved system availability, and an inner control loop tracks the optimal operating point of the PV panel on the fly. Experimental results show that the proposed global controller lowers the task instance drop rate by up to 63% compared with the baseline controller within the same service time (i.e., from sunrise to sunset). 1 The lifetime of a battery is usually less than five years, and in this paper we propose to use supercapacitor instead of battery for embedded systems to prolong the lifespan of the whole system to more than 20 years.

What Could Posturography Tell Us About Balance Problems in Parkinson's Disease?

Impaired balance in patients with Parkinson's disease (PD) leads to loss of balance and frequent falls. Computerized dynamic posturography allows the assessment of stance tasks whereas mobile posturography analyzes the balance in free-field conditions, where falls among PD patients commonly occur (e.g. sitting down or standing up). The aim of the present study is to assess postural stability in PD patients with both techniques. Prospective study. University Hospitals, ambulatory care (outpatient clinic). Thirty-three patients diagnosed with idiopathic PD. Balance assessment. Dizziness handicap inventory (DHI), activities-specific balance confidence scale (ABC), composite score of sensory organization test (SOT), results of free-field body sway analysis (standard balance deficit test (SBDT)), or geriatric SBDT. PD patients showed a significantly higher sway in the roll direction in almost all of the SBDT conditions. Also, pathological sway compared with normative values was more prominent in complex tasks. There is a significant correlation between the different objective variables of the postural study (SOT and SBDT) and the ABC, but not with the DHI. Finally, the percentage of PD patients with a pathological score in SOT-composite score was 54.5% whereas in SBDT-composite score it was significantly higher (93.9%). Mobile posturography is more accurate in depicting the reality of balance impairment in PD patients than platform posturography. Also, ABC relates better than DHI to the significant psychological consequences of balance impairments. An increased lateral trunk sway seems to be a key factor of postural instability in PD patients.