1,720,968 research outputs found
Down Syndrome: gait pattern alterations in posture space kinematics
No full textGait characteristics in Down Syndrome are documented in terms of discrete kinematic variables. However, such features are strictly interrelated and reflect neurological and developmental delays. A phenotypical, quantitative assessment of how multi-joint walking patterns are activated and controlled during gait would enhance the understanding of locomotor mechanisms in such patients. We adopted an analysis framework based on Principal Component Analysis: the gait kinematics of 221 patients aged 6-45 were expressed in terms of a reduced set of one-dimensional movement components. Their time course during the gait cycle was described by score vectors, here called principal positions; its second time derivative, called principal acceleration, characterized the activity of the neuromuscular controller on each component. Outcomes were compared to an age-matched group of 49 healthy individuals. After controlling for the effect of walking speed, we observed that the main alterations in gait patterns emerged in the fourth component which is mostly devoted to stability management (group differences, p<0.001). Rather, the main sagittal-plane locomotor patterns showed only subtle differences from the control group. Using statistical parametrical mapping, we found when (step-to-step transitions) and how (interrelated joints motion) the fourth movement deviated from normal: in particular, an excessive hip adduction and trunk inclination during the transition between single and double support phases. These findings match the neurological and sensorimotor trait of Down Syndrome and suggest the promotion of targeted rehabilitative interventions. Further, this study opens to the adoption of principal positions and principal accelerations to investigate the neuromuscular control of movement patterns during locomotion
Tibial Acceleration-Based Prediction of Maximal Vertical Loading Rate During Overground Running: A Machine Learning Approach
Full text linkGround reaction forces are often used by sport scientists and clinicians to analyze the mechanical risk-factors of running related injuries or athletic performance during a running analysis. An interesting ground reaction force-derived variable to track is the maximal vertical instantaneous loading rate (VILR). This impact characteristic is traditionally derived from a fixed force platform, but wearable inertial sensors nowadays might approximate its magnitude while running outside the lab. The time-discrete axial peak tibial acceleration (APTA) has been proposed as a good surrogate that can be measured using wearable accelerometers in the field. This paper explores the hypothesis that applying machine learning to time continuous data (generated from bilateral tri-axial shin mounted accelerometers) would result in a more accurate estimation of the VILR. Therefore, the purpose of this study was to evaluate the performance of accelerometer-based predictions of the VILR with various machine learning models trained on data of 93 rearfoot runners. A subject-dependent gradient boosted regression trees (XGB) model provided the most accurate estimates (mean absolute error: 5.39 ± 2.04 BW⋅s–1, mean absolute percentage error: 6.08%). A similar subject-independent model had a mean absolute error of 12.41 ± 7.90 BW⋅s–1 (mean absolute percentage error: 11.09%). All of our models had a stronger correlation with the VILR than the APTA (p < 0.01), indicating that multiple 3D acceleration features in a learning setting showed the highest accuracy in predicting the lab-based impact loading compared to APTA.sponsorship: H2020 Interreg EU|Nano4Sports, Research Foundation (Flanders)|FWO.3F0.2015.0048.01, International Society of Biomechanics|dissertation grant program 2019, KU Leuven Research Fund|C32/17/036status: Published onlin
The effect of footwear on postural control in bipedal quiet stance
No full textAssessments of the occurrence of falls in elderly populations reported an increased risk when barefoot as compared to shod conditions, suggesting that footwear has an effect on the postural control system. However, the results of studies analysing static stability in laboratory tests by evaluating the centre of pressure (COP) excursion are inconsistent. The purpose of this study was therefore to investigate the effects of footwear on the postural control system by quantitatively assessing the postural movements executed during quiet stance. The postural movements of 29 subjects were recorded using a standard marker-based motion analysis system. Three footwear conditions were tested: barefoot, a casual athletic shoe and so-called unstable shoes. One-dimensional (1D) principal movement (PM) components were determined by performing a principal component analysis (PCA) on the posture vectors consisting of the 3D coordinates of all markers. The relative contribution of the first five PMs to the entire postural movement, their range of motion and their persistence (detrended fluctuation analysis, DFA) were determined. Repeated-measures analyses of variance (ANOVAs) revealed significant differences between all three shoe conditions. Specifically, when standing in unstable as compared to the normal shoes it was found that higher-order principal components contributed less to the entire movement, that the range of motion in all five PMs was substantially increased, and that the persistence was higher in the first two PMs. When comparing barefoot to normal shoes, it was found that in barefoot standing higher-order principal components contributed less to the entire movement and the persistence was increased in the first and decreased in the third principal component. These results demonstrate that a direct analysis of postural movements reveals additional information about the effect of footwear that is not available from COP measurements
Analisi dei pattern coordinativi del cammino in pazienti con sindrome di Down
No full textLAUREA MAGISTRALELa sindrome di Down (Down Syndrome, DS) è una patologia causata da un’anomalia cromosomica, caratterizzata dalla presenza di una terza copia del cromosoma 21. Se in un soggetto sano il corredo genetico vede la presenza di 46 cromosomi per cellula, 23 di origine materna e 23 di origine paterna, in un soggetto con sindrome di Down il cromosoma 21 è invece presente in triplice copia, da qui il secondo nome con cui è conosciuta questa sindrome, “Trisomia 21”.
Oltre a presentare delle comuni caratteristiche fisiche quali gli occhi a mandorla, il viso rotondo, i piedi piatti e un’altezza contenuta, questa patologia si manifesta con un variabile ritardo nello sviluppo mentale, fisico e motorio. Si ritiene che buona parte dell’alterazione motoria sia legata ad aspetti di natura biomeccanica quali la lassità legamentosa, l’ipotonia muscolare e il piede piatto; tali fattori portano i soggetti con sindrome di Down ad attuare delle strategie compensatorie nella deambulazione.
Tramite l’analisi del cammino (Gait Analysis, GA), sono stati ampiamente indagati in letteratura i principali pattern motori coinvolti in tale movimento, ed è stato dimostrato che determinati parametri spazio-temporali ed alcune grandezze cinematiche come la velocità del cammino, la lunghezza e la larghezza del passo, l’ampiezza e l’andamento nel tempo dei movimenti articolari, sono significativamente alterati nei pazienti con la sindrome di Down. In particolare, nei pazienti con trisomia 21 sono stati confermati una riduzione della velocità di deambulazione, una minore lunghezza e una maggiore larghezza del passo e un ridotto Range of Motion (ROM) delle principali articolazioni degli arti inferiori. Pertanto, pur tenendo conto dell’eterogeneità del cammino dei singoli soggetti, si può affermare che esistono delle caratteristiche del cammino specifiche della sindrome di Down.
L’analisi classica permette quindi di individuare le principali compromissioni funzionali dei soggetti in esame, tuttavia non fornisce informazioni immediate su come vengono coordinati tra loro i vari segmenti corporei. In letteratura non sono ancora presenti ad oggi degli studi sulle strategie cinematiche messe in atto dai soggetti con la sindrome di Down, ovvero mancano degli studi sulle sinergie alle diverse articolazioni.
A tal proposito il presente studio, svolto in collaborazione con il Laboratorio di Analisi del Movimento (Motion Analysis Laboratory, MAL) dell’IRCCS San Raffaele Pisana di Roma, ha lo scopo di indagare i pattern coordinativi del cammino nei pazienti con DS.
È stato analizzato il cammino di 221 pazienti con sindrome di Down di età compresa tra i 6 e i 46 anni (età media: 20.18±9.66 anni), ed è stato confrontato con quello di 49 soggetti sani (Control Group, CG) di età compresa tra i 5 e i 42 anni (età media: 14.76±9.45 anni).
Dopo aver misurato le grandezze antropometriche di interesse per ogni soggetto, è stata effettuata l’acquisizione della cinematica del movimento tramite un sistema optoelettronico (Sistemi ELITE 2002 e SMART-D, BTS SpA, Milano, Italia). Sono state rilevate le coordinate tridimensionali di 22 marker passivi posizionati sul corpo dei soggetti secondo il protocollo Davis. Per ogni partecipante è stato estrapolato un ciclo del passo (definito da due heel-strike) tramite un software dedicato (SMART Analyzer, BTS Spa, Milano, Italia).
Dalle grandezze antropometriche e dagli acquisiti dati cinematici dei marker, sono state ottenute le traiettorie di 14 punti di riferimento, detti landmark: 6 centri articolari e 8 punti di repere anatomici. Questi dati sono stati successivamente elaborati in ambiente Matlab (Mathworks Inc., Natwick, USA).
Nella fase di pre-elaborazione, le traiettorie dei landmark sono state filtrate con un filtro Butterworth passa-basso (frequenza di taglio pari a 15 Hz), quindi i dati sono stati ricampionati su 100 frames. È stato creato un nuovo sistema di riferimento solidale con il soggetto, ed è stata effettuata la sottrazione della postura media per poter studiare le variazioni posturali rispetto alla posizione neutra. Infine le coordinate sono state normalizzate al fine di minimizzare le differenze antropometriche tra i soggetti.
È stata definita come “postura” la configurazione dei landmark in ogni istante di tempo; per ogni prova è stata definita una matrice Pk contenente tutte le posture del k-esimo soggetto durante un ciclo del passo. Una volta assemblate le matrici Pk di tutti i soggetti in un’unica Matrice Globale P, questa è stata analizzata attraverso l’Analisi delle Componenti Principali (Principal Component Analysis, PCA), ottenendo in output tre variabili: gli autovettori della matrice di covarianza di P, detti anche Componenti Principali (Principal Components, PCs); gli autovalori della matrice di covarianza di P, che quantificano la varianza di ogni componente; un insieme di serie temporali (Scores), dette anche Posizioni Principali (Principal Positions, PPs), che descrivono il corso temporale di ogni componente.
Tramite le suddette variabili sono stati ricostruiti i Movimenti Principali (Principal Movements, PMs) come proiezioni delle PCs sulle posizioni principali. Infine, sono state calcolate le derivate seconde delle PPs, dette Accelerazioni Principali (Principal Accelerations, PAs), come espressione del controllo del movimento.
Nella post-elaborazione, per valutare il contributo di ciascuna componente sul movimento globale è stata calcolata l’Ampiezza Relativa (Relative Amplitude, RA) e, per quantificare il controllo dedicato ad ogni pattern, è stato calcolato il Valore Quadratico Medio (Root-Mean-Square, RMS) delle accelerazioni principali.
Per analizzare le differenze nelle serie temporali delle PPs e delle PAs tra i due gruppi (DS e CG), è stata effettuata una Mappatura Statistica Parametrica (Statistical Parametrical Mapping, SPM). Il livello di significatività è stato posto all’1% (α=0.01). Nell’analisi post-hoc è stata applicata al p-value la correzione di Sidak: dopo adeguati confronti aggiuntivi, la soglia critica è stata fissata a p=0.00503.
Poiché, come documentato in letteratura, la velocità del cammino dei pazienti con la sindrome di Down è significativamente inferiore rispetto a quella dei soggetti sani, e questa caratteristica influenza notevolmente l’ampiezza di RA e RMS, è stato necessario minimizzare tale dipendenza tramite l’utilizzo di un modello con legge di potenza.
L’Analisi della Covarianza (ANCOVA) è stata eseguita per confrontare le tendenze dei gruppi in relazione all’età e per valutare la velocità del cammino tra i gruppi, sempre con l’età come covariata.
Dai risultati dello studio, la velocità media del cammino dei pazienti con DS (0.76±0.18 m/s) è significativamente inferiore rispetto a quella del gruppo di controllo (1.08±0.20 m/s, p<0.001), e tende ad aumentare con l’età solo per quest’ultimo gruppo (età × interazione tra gruppi, p=0.002).
I primi quattro PMs spiegano più del 95% della varianza dei dati originali, e in particolare i primi due descrivono i principali pattern che avvengono nel piano sagittale, come la flesso-estensione asincrona delle anche e delle ginocchia; il terzo esprime il movimento sincrono della rotazione esterna dell’anca e la flessione del ginocchio durante l’assorbimento del carico; il quarto descrive il movimento sincrono di adduzione dell’anca e di estensione del ginocchio e l’inclinazione laterale del tronco durante la fase appena successiva al doppio appoggio. Pertanto, quest’ultimo movimento principale viene associato al controllo della stabilità durante la transizione tra un passo e l’altro, e in particolare alle strategie compensatorie messe in atto dal soggetto patologico.
La novità principale di questo studio è l’identificazione dei pattern coordinativi del cammino dei pazienti con sindrome di Down. Il vantaggio primario consiste nell’ottenere un quadro immediato e quantitativo del fenotipo motorio. Infatti, nonostante il riconoscimento dell’importanza della valutazione tradizionale della cinematica articolare, occorre osservare che questa tipologia di analisi non rende direttamente possibile lo studio delle sinergie delle diverse articolazioni. Invece, con i Movimenti Principali è possibile ottenere un metodo diretto per quantificare la cinematica multi-articolare, e in particolare la sinergia messa in atto dalle diverse articolazioni in un pattern specifico. Dai risultati ottenuti è stato possibile identificare le differenze tra il pattern motorio patologico e quello sano, si è evidenziato come viene organizzato il cammino e quali sono le strategie compensatorie messe in atto dai soggetti con DS.
Un’ulteriore innovazione apportata dal presente lavoro è che viene analizzata la natura delle accelerazioni principali durante il cammino come sistema di controllo di questo specifico pattern motorio. In particolare, le PAs rappresentano le accelerazioni tra i vari segmenti corporei e sono associate alle forze attivate dal sistema muscolare, pertanto rispecchiano il controllo che viene profuso in un determinato pattern.
Questi risultati possono essere utili ai fini della pianificazione di interventi terapeutici e riabilitativi specifici per il recupero e il potenziamento delle abilità motorie.Down Syndrome (DS) is a pathology caused by a chromosomal alteration, characterized by the presence of a third copy of chromosome 21. If in a healthy subject the genetic make-up sees the presence of 46 chromosomes per cell, 23 of maternal origin and 23 of paternal origin, in a person with Down syndrome chromosome 21 is instead present in triplicate, hence the second name with which this syndrome is known, "Trisomy 21".
Besides presenting the common physical characteristics such as almond eyes, round face, flat feet and a contained height, this syndrome manifests itself with a variable delay in cognitive, physical and motor development. It is believed that most of the motor alteration is linked to biomechanical aspects such as ligamentous laxity, muscular hypotonia and flatfoot; all these factors lead the subjects with Down syndrome to actuate gait compensatory strategies.
Using Gait Analysis (GA), walking principal motor patterns had been largely investigated, and it was demonstrated that spatio-temporal and kinematic parameters such as walking velocity, step length, step width and amplitude and temporal course of joint movements are significantly altered in DS patients. In particular, it was confirmed a reduction in velocity and stride length, an increased step width and a limited Range of Motion (ROM) in patients with Trisomy 21. Therefore, while considering the heterogeneity of the single subject way of walking, it can be said that there are specific characteristics of the gait of Down syndrome patients.
GA makes it possible to identify the main functional impairments of the subjects under examination, however it does not provide immediate information on how the various body segments are coordinated. In literature, studies on kinematic strategies implemented by subjects with Down syndrome are not yet present, i.e. studies on joint synergies are lacking.
In this regard, the present study, carried out in collaboration with the Motion Analysis Laboratory (MAL) of IRCCS San Raffaele Pisana in Rome, aims to investigate the motor patterns of walking function in patients with Down syndrome.
The gait of 221 patients with Down syndrome aged between 6 and 46 years (mean age: 20.18±9.66 years) was analyzed and compared with that of 49 healthy subjects (Control Group, CG) aged between 5 and 42 years (mean age: 14.76±9.45 years).
After collecting the anthropometric measures for each subject, the acquisition of the kinematics was carried out through an optoelectronic system (ELITE Systems 2002 and SMART-D, BTS SpA, Milan, Italy) that recorded the 3D coordinates of 22 passive markers positioned on the body of the subjects, according to the Davis protocol.
For each subject, a gait cycle (defined by two heel-strikes) was extrapolated through a dedicated software (SMART Analyzer, BTS SpA, Milan, Italy).
From the anthropometric measures and from the acquired kinematic data of markers, the trajectories of 14 landmarks were obtained: 6 joint centres and 8 anatomical landmarks. These data were subsequently processed in Matlab environment (Mathworks Inc., Natwick, USA).
In a pre-processing phase, landmarks trajectories were filtered through a low-pass Butterworth filter (cut-off frequency=15 Hz), then they were re-sampled over 100 frames. A new reference system fixed on the subject was defined and the subtraction of the average posture was carried out in order to study postural changes with respect to the neutral position. Finally, landmarks coordinates have been normalized in order to minimize the anthropometric differences between the subjects.
For each temporal frame, the landmark configuration was defined as "posture", so for each test a Pk matrix was defined containing all the postures of the k-th subject during a gait cycle. Once the Pk matrices of all subjects were assembled into a single Global Matrix P, this was analyzed through the Principal Component Analysis (PCA), obtaining three variables in output: the eigenvectors of the covariance matrix of P, also called Principal Components (PCs); the eigenvalues of the covariance matrix of P, which quantify the variance of each component; a set of time series (Scores), also called Principal Positions (PPs), which describe the time course of each component.
Through the aforementioned variables, the Principal Movements (PMs) were reconstructed as PCs projections onto the principal positions. Finally, the second derivatives of the PPs have been calculated as an expression of movement control, and they were called Principal Accelerations (PAs).
In a post-processing phase, in order to assess the contribution of each component on the global movement, the Relative Amplitude (RA) was calculated and, to quantify the amount of control dedicated to each pattern, the Root Mean Square (RMS) of the principal accelerations was determined.
To analyze the differences in the time series of PPs and PAs between the two groups (DS and CG), a Statistical Parametrical Mapping (SPM) was performed. The significance threshold was set at 1% (α=0.01). In the post-hoc analysis the Sidak correction was applied to the p-value: after adequate additional comparisons, the significance level was set at p=0.00503.
As documented in the literature, the walking speed of patients with Down syndrome is significantly lower than that of healthy subjects, and this feature greatly influences the amplitude of RA and RMS, so it was necessary to minimize this dependence through the use of a model with power law.
The Covariance Analysis (ANCOVA) was performed to compare the groups’ tendency with respect to the age and to assess the walking speed between groups, always with age as covariate.
From the results of the study, the average gait velocity of patients with DS (0.76±0.18 m/s) is significantly lower than that of the control group (1.08±0.20 m/s, p<0.001), and it tends to increase with age only for the latter group (age × group interaction, p=0.002).
The first four PMs explain more than 95% of the variance of the original data, and in particular the first two describe the main patterns that occur in the sagittal plane, such as the asynchronous flex-extension of hips and knees; the third one expresses the synchronous movement of the external rotation of the hip and the flexion of the knee during load absorption; the fourth one describes the synchronous movement of hip adduction and knee extension and the lateral inclination of the trunk just after the double support. Therefore, this last principal movement is associated with the stability control during the step-to step transition, and in particular with the compensatory strategies implemented by the pathological subject.
The main novelty of this study is the identification of the multi-joint walking patterns of patients with Down syndrome. The primary advantage consists in obtaining an immediate and quantitative picture of the motor phenotype. In fact, despite the recognition of the importance of the traditional evaluation of joint kinematics, it should be noted that this type of analysis does not make it directly possible to study the synergies of the various joints. Instead, with the Principal Movements it is possible to obtain a direct method to quantify the multi-joint kinematics, and in particular the synergy implemented by the different joints in a specific motor pattern. From the results obtained it was possible to identify the differences between the pathological motor pattern and the healthy one, it was highlighted how the gait is organized and what are the compensatory strategies implemented by the subjects with DS.
A further innovation introduced by the present work is that the nature of the principal accelerations during walk is analyzed as the control system of this specific motor pattern. In particular, the PAs represent the accelerations between the various body segments and are related to the activated forces, therefore they reflect the control that is lavished on a given pattern.
These results can be useful for planning specific therapeutic and rehabilitative interventions for recovery and enhancement of motor skills
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
