What COP and Kinematic Parameters Better Characterize Postural Control in Standing Balance Tasks?

The authors’ aim was to determine which variables allow for the characterization of motor balance behavior. Traditional measures and nonlinear measures of center of pressure (COP; n D 30) and kinematics (n D 10) were tested in their absolute and relative consistency in a 30-s standing balance task protocol under stable and unstable conditions. Regarding COP variables, mean velocity (mVel), permutation entropy (PE) and detrended fluctuation analysis (DFA) exhibited high consistency between trials and ranked individuals more accurately compare with other metrics. In the kinematic signal mVel, PE and DFA had good intrasession reliability values in unstable conditions. Overall, the intrasession reliability values were better in the unstable condition than in the stable condition and the measures calculated using derived data had better intrasession reliability values. In conclusion, mVel, PE, and DFA allow for the good characterization of motor balance behavior in a simplified protocol where velocity time series are analyzed

Modelos de simulación para el estudio del sistema de catenaria rígida: comportamiento de la estructura e interacción dinámica pantógrafo-catenaria

El presente Trabajo Fin de Grado forma parte de un proyecto real más amplio acerca de simulación del sistema de catenaria rígida desarrollado en el departamento de Ingeniería Gráfica de la ETSII. El sistema ferroviario de captación de corriente más antiguo y más extendido corresponde al sistema de catenaria flexible o convencional, existiendo numerosos estudios acerca de su comportamiento y de la interacción pantógrafo – catenaria (flexible) La catenaria rígida constituye el otro sistema de captación de corriente más empleado. La estructura de este sistema está compuesta por cuatro elementos principales: carril conductor de aluminio, hilo de contacto, bridas de unión y soportes. Este sistema presenta ciertas ventajas con respecto a la catenaria convencional y además se trata de una tecnología emergente, por lo que resulta muy interesante estudiarla más en profundidad. El objetivo de este proyecto consiste en crear un modelo válido de catenaria rígida, que permita simular su comportamiento tanto estático como dinámico y estudiar la interacción dinámica pantógrafo – catenaria (rígida)

Role of vision in sighted and blind soccer players in adapting to an unstable balance task

This study tested whether a compensatory hypothesis exists on postural control during standing unstable balance tasks comparing blind soccer players (n = 7) to sighted soccer players (n = 15) and sighted sedentary individuals (n = 6). All subjects performed a pre-test, a training of ten practice trials on a single day, and a post-test balance test. All tests were performed on an unstable surface placed on a force platform and under closed-eyes conditions, and a final test was performed with open eyes. Balance performance was assessed by resultant distance (RD) and the magnitude of mean velocity (MV) of the centre of pressure (CoP) displacement, and EMG signals from the gastrocnemius lateralis, tibialis anterior, rectus femoris, and peroneus longus were measured with surface electromyography. Principal component analysis (PCA) on EMG muscular activation was used to assess EMG pattern differences during the balance tasks. All groups improved their performance, obtaining low scores for the closed-eyes condition balance task after the training period in RD, VM, and aids received to keep balance in the novel task, and no differences were found between groups or in interaction effects. Sighted individuals and the control group showed significantly lower RD and VM scores under open-eyes conditions than blind participants. As regards neuromuscular behaviour, three principal patterns explained 84.15% of the variability in the measured data. The theoretical improvement of the other senses caused by visual deprivation does not allow blind individuals to obtain better balance than sighted individuals under closed-eyes conditions, thereby reinforcing the prominent role of vision in integrating and processing the other sensory inputs. In addition, blind individuals seem to increase their muscular co-activation as a safety strategy, but this behaviour is not different to that shown by sighted people under closed-eyes conditions

Test de camp per valorar la resistència dels músculs del tronc

El test Biering-Sorensen (BST), el test Side Bridge (SBT) i el test Ito (IT) són tres dels tests de camp més utilitzats per mesurar la resistència dels músculs del tronc. L’objectiu d’aquest estudi va ser analitzar la fiabilitat absoluta i relativa dels tests referits, així com valorar-ne l’efecte en el rendiment de l’antropometria dels participants en les proves. En l’estudi van participar 27 joves homes (23,5 ± 4,0 anys) i físicament actius. Els participants van fer dues sessions de registre en què van executar els tres tests (recuperació de 8 min entre proves) i on es van mesurar diverses variables antropomètriques. La fiabilitat relativa va ser bona, amb ICC majors de 0,80 en tots els tests, però la fiabilitat absoluta no, amb SEM que van oscil·lar entre 13,36 % en el BST i 19,89 % en l’IT. L’IT va mostrar una correlació negativa amb la massa (r = – ,475; p = ,014) i el diàmetre bileocrestal (r = – ,404; p = ,040), i el SBT una correlació negativa amb la massa (r = – ,610; p = ,001), el diàmetre bileocrestal (r = – ,546; p = ,004), el diàmetre biacromial (r = – ,456; p = ,019) i l’índex acromioilíac (r = – ,413; p = ,036). Les dades de fiabilitat absoluta qüestionen la utilitat d’aquestes proves en programes d’entrenament on els participants tenen poc marge de millora. A més a més, si es fan comparacions entre subjectes és important tenir en compte les seves diferències antropomètriques, ja que durant l’execució dels tests el cos s’utilitza com a instrument de mesura

Tests to measure core stability in laboratory and field settings: reliability and correlation analyses

Although core stability (CS) has been assessed through many different tests, the relationships among them are currently unknown. The main objective was to analyse the relationship between five representative tests used to assess CS in: i) laboratory settings: Sudden Loading Test (SLT) and Stable and Unstable Sitting Test (SUST); ii) field settings: Biering-Sorensen Test (BST), Three-Plane Core Strength Test (TPCT) and Double-leg Lowering Test (DLLT). The reliability of these tests was also examined. Thirty-three recreationally active males performed the tests twice. The relationship between all variables was examined using Pearson-correlation coefficient in those variables with a good reliability. Only stiffness and angular displacement in the SLT, dynamic unstable tasks in the SUST and the holding-time in the BST showed good reliability (ICC: 0.63-0.91; typical error: 9.8%-21.0%). Few and low correlations were observed between the SLT, SUST and BST. Despite finding several significant correlations among the dynamic unstable tasks of the SUST (r≥0.807; p<0.01), no correlations were found between the loading directions of the SLT. The absence of correlations between these tests suggests that CS measurements are not generalisable, as they probably assess different dimensions of CS, or in the case of the BST, a different capacity (i.e. trunk extensor endurance)

Can the structure of motor variability predict learning rate?

Recent studies show that motor variability is actively regulated as an exploration tool to promote learning in reward-based tasks. However, its role in learning processes during error-based tasks, when a reduction of the motor variability is required to achieve good performance, is still unclear. In this study, we hypothesized that error-based learning not only depends on exploration but also on the individuals’ ability to measure and predict the motor error. Previous studies identified a less auto-correlated motor variability as a higher ability to perform motion adjustments. Two experiments investigated the relationship between motor learning and variability, analyzing the long-range autocorrelation of the center of pressure fluctuations through the score of a Detrended Fluctuation Analysis in balance tasks. In Experiment 1, we assessed the relationship between variability and learning rate using a standing balance task. Based on the results of this experiment, and to maximize learning, we performed a second experiment with a more difficult sitting balance task and increased practice. The learning rate of the 2 groups with similar balance performances but different scores was compared. Individuals with a lower score showed a higher learning rate. Because the scores reveal how the motor output changes over time, instead of the magnitude of those changes, the higher learning rate is mainly linked to the higher error sensitivity rather than the exploration strategies. The results of this study highlight the relevance of the structure of output motor variability as a predictor of learning rate in error-based tasks

Test de campo para valorar la resistencia de los músculos del tronco

El Biering-Sorensen test (BST), el Side Bridge test (SBT) y el Ito test (IT) son tres de los test de campo más utilizados para medir la resistencia de los músculos del tronco. El objetivo de este estudio fue analizar la fiabilidad absoluta y relativa de los test referidos, así como valorar el efecto de la antropometría de los participantes en el rendimiento en las pruebas. En el estudio participaron 27 jóvenes varones (23,5 ± 4,0 años) y físicamente activos. Los participantes realizaron dos sesiones de registro en las que ejecutaron los tres test (recuperación de 8 min entre pruebas) y donde se midieron diversas variables antropométricas. La fiabilidad relativa fue buena, con ICC mayores de 0.80 en todos los test, pero no así la fiabilidad absoluta, con SEM que oscilaron entre el 13,36 % en el BST y el 19,89 % en el IT. El IT mostró una correlación negativa con la masa (r= – ,475; p= ,014) y el diámetro bileocrestal (r = – ,404; p = ,040) y el SBT una correlación negativa con la masa (r = –,610; p = ,001), el diámetro bileocrestal (r = –,546; p = ,004), el diámetro biacromial (r= - ,456; p = ,019) y el índice acromioiliaco (r= –,413; p = ,036). Los datos de fiabilidad absoluta cuestionan la utilidad de estas pruebas en programas de entrenamiento donde los participantes tienen poco margen de mejora. Además, si se realizan comparaciones entre sujetos es importante tener en cuenta sus diferencias antropométricas, ya que durante la ejecución de los test el cuerpo se utiliza como instrumento de medida

EFFECT OF PERFORMANCE SPEED ON THE KINEMATICS AND KINETICS OF TWO TRUNK AND HIP STRENGTHENING EXERCISES

The aim of this work was to study the effect of speed on the sit-up (SU) and leg raising-lowering (LRL) exercise technique. Seventeen subjects volunteered to participate, performing at 3 cadences. Video 3D analysis was conducted and ground reaction forces were record. The anterior-posterior displacement of the centre of pressure (COP) and mean range of motion (ROM) for 6 angles were calculated. Results indicate that when SU speed increases, hip and knee ROM increase, while there is a decrease in the upper trunk flexion. In the LRL there is a decrease in the pelvic tilt and hip angle, and an increase in the knee angle. It seems that in higher speed exercises, subjects modified their technique to keep up with the cadence. Coaches and trainers should control the subjects’ technique during the execution of these high speed exercises

The role of motor variability in motor control and learning depends on the nature of the task and the individual’s capabilities

Recent studies have found that motor variability is actively regulated as an exploration tool to promote learning in reward and error-based tasks. Based on this functional role of variability, several researches have manipulated motor variability by practicing in order to maximize learning processes. However, the effectiveness of such variable practice as a tool to improve motor performance has shown several controversial results. The present work reviews how the interaction between the features of individuals with different motor capabilities (i.e. experience and brain disorders) and task constraints modulates the relation between motor variability and motor control and learning. Examining how the process of skill learning can be improved by the variability modulation according to individuals’ is not only of theoretical interest, but may also have several practical implications in motor learning and neuro-rehabilitation.Estudios recientes han demostrado que la variabilidad motora es activamente regulada como herramienta de exploración con objeto de incrementar el rendimiento motor tanto en tareas de aprendizaje basadas en la aplicación de recompensas como en la percepción del error. Basándose en este rol funcional de la variabilidad, varios investigadores han manipulado la variabilidad motora al practicar para maximizar los procesos de aprendizaje motor. Sin embargo, la efectividad de la práctica variable como herramienta para la mejora de la ejecución motora, ha mostrado resultados contradictorios en la literatura científica. El presente trabajo revisa cómo la interacción entre las características de individuos con diferentes capacidades motrices (i.e. experiencia y alteraciones neurológicas) y las características de las tareas modulan la relación entre la variabilidad motora, el control y el aprendizaje motor. El estudio de cómo los procesos de aprendizaje motor pueden ser mejorados mediante la manipulación de la carga de variabilidad al practicar no tiene sólo un interés teórico, sino que puede tener implicaciones prácticas en relación al aprendizaje motor o la neuro-rehabilitación