Sina Mehdizadeh

Sina Mehdizadeh
Simon Fraser University · Department of Biomedical Physiology and Kinesiology

PhD

About

50
Publications
19,413
Reads
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291
Citations
Introduction
My research interests are the application of dynamical systems theory (DST) and nonlinear dynamics to study stability and coordination in human movement and sports activities.
Additional affiliations
June 2015 - present
Iran University of Medical Sciences
Position
  • Researcher
June 2015 - present
Tehran University of Medical Sciences
Position
  • Researcher

Publications

Publications (50)
Article
Drug-induced parkinsonism affects many older adults with dementia, often causing gait disturbances. New advances in vision-based human pose-estimation have opened possibilities for frequent and unobtrusive analysis of gait in long-term care settings. This work leverages spatial-temporal graph convolutional network (ST-GCN) architectures and trainin...
Article
Full-text available
People with dementia are at risk of mobility decline. In this study, we measured changes in quantitative gait measures over a maximum 10-week period during the course of a psychogeriatric admission in older adults with dementia, with the aims to describe mobility changes over the duration of the admission, and to determine which factors were associ...
Preprint
Data consists of baseline clinical assessments of gait, mobility, and fall risk at the time of admission of 54 adults with dementia. Furthermore, it includes the participants' daily medication intake in three medication categories, and frequent assessments of gait performed via a computer vision-based ambient monitoring system.
Preprint
Data consists of baseline clinical assessments of gait, mobility, and fall risk at the time of admission of 54 adults with dementia. Furthermore, it includes the participants' daily medication intake in three medication categories, and frequent assessments of gait performed via a computer vision-based ambient monitoring system.
Conference Paper
Older adults with dementia have a high risk of developing drug-induced parkinsonism; however, formal clinical gait assessments are too infrequent to capture fluctuations in their gait. Camera-based human pose estimation and tracking provides a means to frequently monitor gait in nonclinical settings. In this study, 2160 walking bouts from 49 partic...
Article
Full-text available
Background Many of the available gait monitoring technologies are expensive, require specialized expertise, are time consuming to use, and are not widely available for clinical use. The advent of video-based pose tracking provides an opportunity for inexpensive automated analysis of human walking in older adults using video cameras. However, there...
Preprint
Full-text available
Drug-induced parkinsonism affects many older adults with dementia, often causing gait disturbances. New advances in vision-based human pose-estimation have opened possibilities for frequent and unobtrusive analysis of gait in residential settings. This work proposes novel spatial-temporal graph convolutional network (ST-GCN) architectures and train...
Article
Full-text available
Whether higher variability in older adults’ walking is an indication of increased instability has been challenged recently. We performed a computer simulation to investigate the effect of sensorimotor noise on the kinematic variability and stability in a biped walking model. Stochastic differential equations of the system with additive Gaussian whi...
Article
Measures of gait center of pressure (COP) can be recorded using simple available technologies in clinical settings and thus can be used to characterize gait quality in older adults and its relationship to falls. The aim of this systematic review was to investigate the association between measures of gait COP and aging and falls. A comprehensive sea...
Article
Objectives: To develop a prognostic model to predict the probability of a short-term fall (within the next 7 to 30 days) in older adults with dementia. Design: Prospective observational study. Setting and participants: Fifty-one individuals with dementia at high risk of falls from a specialized dementia inpatient unit. Methods: Clinical and...
Article
Full-text available
Background: Parkinsonism is common in people with dementia, and is associated with neurodegenerative and vascular changes in the brain, or with exposure to antipsychotic or other dopamine antagonist medications. The detection of parkinsonian changes to gait may provide an opportunity to intervene and address reversible causes. In this study, we in...
Article
Full-text available
Fall risk is high for older adults with dementia. Gait impairment contributes to increased fall risk, and gait changes are common in people with dementia, although the reliable assessment of gait is challenging in this population. This study aimed to develop an automated approach to performing gait assessments based on gait data that is collected f...
Article
Introduction People living with dementia are at higher risk of falling than cognitively healthy older adults, and the consequences of falls are severe. Psychotropic medication is an important risk factor for falls, but their effect on gait stability in people with dementia is not well-understood. In this study, we use vision-based gait assessment t...
Article
Full-text available
Background: Return to sport (RTS) criteria are widely being used to identify anterior cruciate ligament reconstructed (ACLR) athletes ready to return to sportive activity and reduce risk of ACL re-injury. However, studies show a high rate of ACL re-injury in athletes who passed RTS criteria. This indicates that the current RTS criteria might not b...
Preprint
The development of methods that can identify athlete-specific optimum sports techniques—arguably the holy grail of sports biomechanics—is one of the greatest challenges for researchers in the field. This ‘perspectives article’ critically examines, from a dynamical systems theoretical standpoint, the claim that athlete-specific optimum sports techni...
Article
Background Gait impairments contribute to falls in people with dementia. In this study, we use a vision-based system to record episodes of walking over a two week period as participants moved naturally around their environment, and from these calculated spatiotemporal, stability, symmetry, and acceleration gait features. The aim of this study was t...
Article
Background: Rigid-rocker shoes may induce gait instability in diabetics, however, this is not clearly investigated. The present study investigates if rigid-rocker shoes influence diabetic gait stability. Methods: Fourteen non-neuropathic and nine neuropathic diabetics, plus eleven healthy young-adults were recruited. Full-body kinematic data was...
Article
Full-text available
This paper evaluates the effectiveness of, and highlights issues with, conventional paradigms in applied sports biomechanics research and comments on their capacity to optimise techniques of individual athletes. In empirical studies, group-based analyses often mask variability between athletes and only permit probabilistic ‘in general’ or ‘on avera...
Preprint
This paper evaluates the effectiveness of, and highlights issues with, conventional paradigms in applied sports biomechanics research and comments on their capacity to optimise techniques of individual athletes. In empirical studies, group-based analyses often mask variability between athletes and only permit probabilistic ‘in general’ or ‘on avera...
Preprint
Full-text available
Low stability and asymmetrical gait are two important challenges in gait of individuals with trans-tibial amputation. The aim of this case report was to determine the feasibility and effectiveness of a real-time video feedback of foot placement on stability (i.e. foot placement regularity) and symmetry of trans-tibial amputees. Furthermore, we aime...
Preprint
Full-text available
Aim This study proposed a revision to the Rosenstein’s method of numerical calculation of largest Lyapunov exponent (LyE) to make it more robust to noise. Methods To this aim, the effect of increasing number of initial neighboring points on the LyE value was investigated and compared to the values obtained by filtering the time series. Both simula...
Preprint
The aims of this study were to demonstrate “order error” in the calculation of continuous relative phase (CRP) and to suggest two alternative methods—(i) constructing phase-plane portraits by plotting position over velocity; and (ii), the Hilbert transform—to rectify it. Order error is the change of CRP order between two degrees of freedom (e.g., b...
Article
The aims of this study were to demonstrate “order error” in the calculation of continuous relative phase (CRP) and to suggest two alternative methods—(i) constructing phase-plane portraits by plotting position over velocity; and (ii), the Hilbert transform—to rectify it. Order error is the change of CRP order between two degrees of freedom (e.g., b...
Article
The largest Lyapunov exponent (LyE) is an accepted method to quantify gait stability in young and old adults. However, a range of LyE values have been reported in the literature for healthy young and elderly adults in normal walking. Therefore, it has been impractical to use the LyE as a clinical measure of gait stability. The aims of this systemat...
Article
This study aimed to determine the effect of added noise, filtering and time series length on the largest Lyapunov exponent (LyE) value calculated for time series obtained from a passive dynamic walker. The simplest passive dynamic walker model comprising of two massless legs connected by a frictionless hinge joint at the hip was adopted to generate...
Article
Full-text available
Anterior cruciate ligament injury is a debilitating pathology which may alter lower limb coordination pattern in both intact and affected lower extremities during activities of daily living. Emerging evidence supports the notion that kinematic variables may not be a good indicator to differentiate patients with anterior cruciate ligament deficiency...
Data
Mean ensemble coordination pattern and coordination variability. (XLSX)
Data
Ankle, knee and hip joint angles. (XLSX)
Data
Foot, shank and thigh segment angles. (XLSX)
Data
Laboratory set-up, marker setting and initial position. (TIF)
Article
Full-text available
Abstract The aim of this study was to investigate effects of speed and plane of motion on stability during locomotion in skilled football players. Ten male national-level football players participated in this study to run forward, backward and in lateral directions on a treadmill at 80%, 100% and 120% of their preferred running speeds. The coordina...
Article
Abstract Agility is an essential part of many athletic activities. Currently, agility drill duration is the sole criterion used for evaluation of agility performance. The relationship between drill duration and factors such as acceleration, deceleration and change of direction, however, has not been fully explored. This paper provides a mathematica...
Article
This study implemented linear and nonlinear methods of measuring variability to determine differences in stability of two groups of skilled (n = 10) and unskilled (n = 10) participants performing 3m forward/backward shuttle agility drill. We also determined whether stability measures differed between the forward and backward segments of the drill....
Article
Full-text available
Abstract A number of studies have investigated effects of speed on local dynamic stability of walking, although this relationship has been rarely investigated under changing task constraints, such as during forward and backward running. To rectify this gap in the literature, the aim of this study was to investigate the effect of running speed on lo...
Conference Paper
Agility is the ability to change the body direction while maintaining dynamic balance, coordination, speed. This is achieved by acceleration, deceleration and change of direction. When viewed from the stand point of the Dynamical System Theory (DST), Agility could be described as a series of complex movements where coordinated body segments perform...
Conference Paper
Most of CP patients, especially those with severe CP, spend much of their time sitting to perform vital tasks of daily life. In this single subject specific study, the objective is to identify cerebral palsy trunk muscles activity in sitting position. Three dimensional single and double inverted pendulum models are used to study upper body movement...
Article
Full-text available
Characterizing the differences between the mechanical properties of brain tissue gray and white matters is of importance in biomechanics of brain tissue and may find a variety of different applications in medicine. In this study, a comparison has been made between mechanical behavior of bovine brain tissue white and gray matters. Through a linear e...

Questions

Questions (8)
Question
What are the initial conditions (x0, x0dot) for the simplest passive dynamic walker (introduced by Garcia et al.) to get period 2, 4, etc (not period 1) gait?
Question
Hi Dr Van Dieen,
I'd like to know if this project focuses on standing balance only or you are considering balance training for walking as well?
Question
In modeling biologic rhythmic actions as limit-cycles, it has been reported that a negative Duffing term (i.e. -x^3) represents decreasing of variability near reversal points (or softening spring). The question is what type of "variability" we mean here? Spatial? Temporal? Any other type?
How could it be proved or visualized based on Duffing equations or any other method that variability decreases near reversal points?
Question
I am trying to propose a limit cycle model for a movement using "W" method. In this regard, I am going to find the coefficients of the proposed model (i.e. diff. equation) using multiple regression method. Then, I solve the diff. equation using previously found coefficient and plot the results. However, the result is not a limit cycle. Alternatively, when I manipulate the signs of the coefficients to what it should be, the results will be a limit cycle. Why the signs of coefficients are not correct when using regression method? Does it mean the proposed model is not the model that fits the data?
Question
According to Floquet theory, for a system to be orbitally stable, the magnitude of all FMs should be less than 1. However, as I know, it is not mentioned in the literature that if a system with smaller value of maxFM (say for example maxFM=0.5) is orbitally more stable than another system with greater maxFM (e.g maxFM=0.9).
Question
Many studies have quantified orbital dynamic stability (measured using Floquet Multipliers) in walking. The question is should running also be orbitally stable?
Question
Consider we are performing a repeated measure in ANOVA over three conditions. In addition, there are for example 10 measurements at each condition. The result of a linear contrast as part of a repeated measure output in SPSS is different to the results of a linear regression conducted using mean values of each condition. Why does this occur and which one should be reported?
Question
Since three points are not sufficient to perform a quadratic regression, are there other methods for fitting a quadratic model which is capable of testing statistical significance?

Projects