Sharif Digital Repository

Background and Aim: Aging often results in a decline in somatosensory function, and such changes are associated with diminished motor performance. Input noise can enhance sensory and motor function through a mechanism known as stochastic resonance (SR). This paper describes the development and testing of a new vibrating shoe to possibly assist the elderly patients in controlling their balance and decreasing their falling risks. Technique: The new vibrating shoe was evaluated to ascertain its ability to generate appropriate random and nonlinear vibrations. The vibratory shoe performance in two young subjects with decreased foot sensation and two elderly subjects in different static and... 

Background: Lumbosacral orthosis (LSO) is commonly used for the treatment of back pain. The clinical and mechanical effectiveness of this device has been repeatedly investigated in several studies; however, its sensorimotor effectiveness has been rarely considered. Regarding this, the aim of the current study was to investigate the effect of a non-extensible LSO on postural stability (as a construct of sensorimotor function) in patients with nonspecific chronic low back pain (LBP). Methods: This preliminary study was conducted on 17 patients with nonspecific chronic LBP using a single-group quasi-experimental design. Postural stability was measured while the participants were placed in a... 

Using an iterative kinematics-driven nonlinear finite element model, relative efficiency of individual abdominal muscles in spinal stability in upright standing posture was investigated. Effect of load height on stability and muscle activities was also computed under different coactivity levels in abdominal muscles. The internal oblique was the most efficient muscle (compared with the external oblique and rectus abdominus) in providing stability while generating smaller spinal loads with lower fatigue rate of muscles. As the weight was held higher, stability deteriorated requiring additional flexor-extensor activities. The stabilising efficacy of abdominal muscles diminished at higher... 

Accurate estimation of muscle forces in various occupational tasks is critical for a reliable evaluation of spinal loads and subsequent assessment of risk of injury and management of back disorders. The majority of biomechanical models of multi-segmental spine estimate muscle forces and spinal loads based on the balance of net moments at a single level with no consideration for the equilibrium at remaining levels. This work aimed to quantify the extent of equilibrium violation and alterations in estimations when such models are performed at different levels. Results are compared with those of kinematics-driven model that satisfies equilibrium at all levels and EMG data. Regardless of the... 

Background: Many studies have been conducted on the changes in the balance capabilities of stroke patients. However, results regarding the effects of dual-task activities on postural control in these patients have been variable. Objective: To evaluate the effects of a short-term memory task on the sway characteristics of stroke patients. Method: Center of pressure (COP) fluctuations were measured in three levels of postural difficulty (rigid surface with closed and open eyes and foamsurface with closed eyes), aswell as two levels of cognitive difficulty (easy and difficult). COP parameters included mean velocity, standard deviation of velocity in both medial-lateral (M.L) and... 

An appropriate combination of the thin-layer Navier-Stokes (TLNS) and parabolized Navier-Stokes (PNS) solvers is used to accurately and efficiently compute hypersonic transitional/turbulent flowfields of perfect gas and equilibrium air around blunt-body configurations. The TLNS equations are solved in the nose region to provide the initial data plane needed for the solution of the PNS equations. Then the PNS equations are employed to efficiently compute the flowfield for the afterbody region by using a space marching technique. Both the TLNS and the PNS equations are numerically solved by using the implicit non-iterative finite-difference algorithm of Beam and Warming. A shock fitting... 

Although several studies have applied traditional linear measures to evaluate postural control of patients with multiple sclerosis (MS), little is known about the nonlinear dynamics of this patient group. In this study, recurrence quantification analysis (RQA), a well documented nonlinear method, was used to compare the nonlinear dynamical structure of postural sway in two groups consisting of MS patients (. n=. 23) and healthy matched controls (. n=. 23). The study focuses on three levels of postural difficulty consisting of (1) standing on a rigid surface (force platform) with eyes open, (2) standing on a rigid surface with eyes closed, and (3) standing on a foam surface with eyes closed.... 

A previous review concluded that postural sway is increased in patients with low back pain (LBP). However, more detailed analysis of the literature shows that postural deficit may be dependent on experimental conditions in which patients with LBP have been assessed. The research question to be answered in this review was: " Is there any difference in postural sway between subjects with and without LBP across several sensory manipulation conditions?" A literature search in Pubmed, Scopus, Embase and PsychInfo was performed followed by hand search and contact with authors. Studies investigating postural sway during bipedal stance without applying external forces in patients with specific and... 

Knowledge about the non-linear dynamical pattern of postural sway may provide important insights into the adaptability (flexibility) of human postural control in response to everyday stresses imposed on the body. A commonly used non-linear tool, i.e. recurrence quantification analysis, was chosen to investigate the effect of prior anterior cruciate ligament injury on the deterministic pattern of postural sway under different conditions of postural and cognitive difficulty. In double leg stance, as postural difficulty increased from open-eyes to closed-eyes and rigid-surface to foam-surface, the centre of pressure regularity (%determinism) increased as well. In comparison to healthy... 

Recurrence quantification analysis (RQA), a nonlinear method of postural analysis, was used to explore the effects of dual-tasking on postural performance in people with nonspecific low back pain (LBP) compared with healthy participants. Postural performance was quantified by RQA % recurrence, % determinism, entropy and trend. People with nonspecific LBP (n = 22) and unimpaired individuals (n = 22) randomly performed quiet standing tasks with three levels of difficulty (rigid-surface eyes open, rigid-surface eyes closed and foam-surface eyes closed). These tasks were performed in isolation or concurrently with an easy or difficult cognitive task. Increasing postural difficulty was associated... 

Background: Foot orthoses are used to optimize lower extremity function and can improve postural stability by enhancing the afferent somatosensory feedback available to the central nervous system. Objective: The aim of this review was to evaluate the effect of foot orthoses on balance control in older subjects. Study design: Systematic review. Methods: The search strategy was based on the Population Intervention Comparison Outcome method. A search was performed in PubMed, Science Direct, Google Scholar, and ISI Web of Knowledge databases by using selected keywords. A total of 22 articles were selected for final evaluation. Results: The results demonstrated that older people should be advised... 

Individuals with spinal cord injury (SCI) at lower thoracic levels might walk independently with the aid of mechanical orthoses and walker by using their unimpaired trunk and upper extremity muscles (TUEM). The required motor skills and the associated subtasks of the paraplegic locomotion, however, have not been well understood yet. The purpose of this study was to investigate the coordination of the TUEM activities throughout the paraplegic gait cycle using synergy analysis. For eight paraplegic individuals (30.6 ± 11.6 years; SCI level: T12), the kinematics data and the surface electromyography (EMG) signals of TUEM were recorded during 15 gait cycles. Non-negative matrix factorization... 

This study aimed to investigate the variability in postural sway patterns during quiet standing in stroke survivors. The postural sway was measured in 19 stroke survivors, as well as 19 healthy demographically matched participants, at 3 levels of postural difficulty (rigid surface with closed and open eyes, and foam surface with closed eyes), and 3 levels of cognitive difficulty (without a cognitive task, easy and difficult cognitive tasks). Both linear analyses (the amount of postural sway variability, including the standard deviation of the COP velocity in both the anteroposterior (AP) and mediolateral (ML) directions), as well as non-linear analyses [the temporal structure of the COP... 

Background Although anxiety is a common non-motor outcome of Parkinson's disease (PD) affecting 40% of patients, little attention has been paid so far to its effects on balance impairment and postural control. Improvement of postural control through focusing on the environment (i.e. external focus) has been reported, but the role of anxiety, as a confounding variable, remains unclear. Objectives This study aimed to investigate the influence of anxiety and attentional focus instruction on the standing postural control of PD patients. Methods Thirty-four patients with PD (17 with high anxiety (HA-PD) and 17 with low anxiety (LA-PD)), as well as 17 gender- and age-matched healthy control... 

Several studies have investigated postural control in anterior cruciate ligament (ACL) deficient patients; yet the contribution of cognitive processing (attention) in the postural control of these patients is still unclear. A dual-task design was used to determine the effects of a concurrent digit span memory task on standing balance in a group of ACL patients (n = 27) compared with a group of matched, healthy participants (n = 27). In double limb stance, three levels of postural difficulty were studies on a force platform (rigid surface with eyes open, rigid surface with eyes closed, and foam surface with eyes closed). There were three cognitive conditions (no cognitive task, easy cognitive... 

Background: Impaired postural control in Parkinson's disease (PD) seriously compromises life quality. Although balance training improves mobility and postural stability, lack of quantitative studies on the neurophysiological mechanisms of balance training in PD impedes the development of patient-specific therapies. We evaluated the effects of a balance-training program using functional balance and mobility tests, posturography, and a postural control model. Methods: Center-of-pressure (COP) data of 40 PD patients before and after a 12-session balance-training program, and 20 healthy control subjects were recorded in four conditions with two tasks on a rigid surface (R-tasks) and two on foam.... 

Although anxiety is one of the most prevalent psychological disorders in stroke survivors, its effect on sensory reweighting has not yet been fully studied. The aim of this work was to investigate how anticipation of collision avoidance events affects sensory reweighting in chronic stroke survivors with low and high levels of anxiety (LA-stroke and HA-stroke, respectively), as compared with healthy controls (HC), under the condition of perturbed proprioception. Eighteen LA-stroke and 18 HA-stroke survivors, as well as 18 gender- and age-matched HC, participated in this study. Postural sway variability (i.e. Root Mean Square (RMS) of the COP velocity) was measured for a duration of 180 s... 

Background: It is important to improve verbal Working Memory (WM) in reading disability, as it is a key factor in learning. There are commercial verbal WM training programs, which have some short-term effects only on the verbal WM capacity, not reading. However, because of some weaknesses in current verbal WM training programs, researchers suggested designing and developing newly structured programs that particularly target educational functions such as reading skills. In the current double-blind randomized clinical trial study, we designed a new Verbal Working Memory-Balance (VWM-B) program which was carried out using a portable robotic device. The short-term effects of the VWM-B program,... 

Although the application of nonlinear tools including recurrence quantification analysis (RQA) has increasingly grown in the recent years especially in balance-disordered populations, there have been few studies which determine their measurement properties. Therefore, a methodological study was performed to estimate the intersession and intrasession reliability of some dynamic features provided by RQA for nonlinear analysis of center of pressure (COP) signals recorded during quiet standing in a sample of patients with musculoskeletal disorders (MSDs) including low back pain (LBP), anterior cruciate ligament (ACL) injury and functional ankle instability (FAI). The subjects completed postural... 

A hallmark of more advanced models is their higher details of trunk muscles represented by a larger number of muscles. The question is if in reality we control these muscles individually as independent agents or we control groups of them called "synergy". To address this, we employed a 3-D biomechanical model of the spine with 18 trunk muscles that satisfied equilibrium conditions at L4/5, with different cost functions. The solutions of several 2-D and 3-D tasks were arranged in a data matrix and the synergies were computed by using non-negative matrix factorization (NMF) algorithms. Variance accounted for (VAF) was used to evaluate the number of synergies that emerged by the analysis, which...