Parkinson's disease (PD) is a neurological condition that can lead to changes to gait and postural stability of people with this condition. Tai Chi (TC) has been recommended for the management of PD by improving muscle strength, balance, and coordination. However, biomechanics research in TC for PD is lacking. This thesis investigated the effects of a biomechanical-based TC intervention program for people in the early-stage of PD by realizing three specific research objectives: 1) to develop a biomechanical-based TC intervention program for PD; 2) to examine the effects of a 12-week TC intervention on gait and postural stability in people with PD, by pre-test and post-test biomechanical analysis of obstacle crossing; 3) to explore the neuromuscular effects of TC intervention on gait and postural stability by analyzing the electromyography (EMG) activity of the lower limb muscles during obstacle crossing. Seven typical TC movements were selected, including Starting Form, Hero Touch Sky, Push Hand Back, Brush Knee and Twist Step, Repulse Monkey, Wave-hand in Cloud, and Lateral Forward Step to develop the TC intervention program. The joint angles, joint moment, and EMG signals of lower limbs muscles were analyzed during performance of the selected TC movements by an experienced TC master aged 38 years. Results showed that the selected TC movements are characterized by multidirectional movements, greater joint movement angles of the lower limb, and more active muscle activity than walking. The TC intervention program was formed based on the biomechanics analysis of the seven TC movements. The program consisted of 5-10 min warm up, 40 minutes of core activities, and 5 min cool down. To examine the effects of a biomechanical-based TC intervention program on gait and postural stability and to explore the neuromuscular effects of TC intervention on the lower limb muscles in people with PD, fifteen individuals in the early stage of PD (n = 15, Hoehn and Yahr stages 1 to 2; age 72.0 ± 6.9) participated in a 12-week online TC intervention, and 15 age- and sex-matched healthy participants (n = 15) served as control. The 3D motion data of the lower limb and EMG signals from the rectus femoris, adductor longus, tibialis anterior, semitendinosus, gluteus medius, tensor fasciae latae, and medial and lateral gastrocnemius muscles were collected during obstacle crossing from both groups using Vicon motion analysis system before intervention in both groups and after TC intervention in the TC group. Obstacle crossing was used to challenge the participants' gait and postural stability. Gait was assessed by measuring the temporospatial parameters such as crossing stride length, crossing step length, and crossing speed. Postural stability was assessed by measuring toe and clearance distance, pre- and post-horizontal distance, displacement and velocity of center of mass (COM), and COM-center of pressure (COP) separation. To examine the neuromuscular activity of the lower limbs following TC training, the ratio of the peak EMG, the integrated EMG (iEMG), and the ratio of the peak EMG and iEMG antagonistic pairs of the leading and trailing limb were examined during obstacle crossing and walking. In addition, the timed up-and-go test (TUG) and single-leg stance with eyes open and closed were tested. VICON Nexus, custom MATLAB scripts, and SPSS software (version 20) were used to analyze the data. Analysis of the PD participants' obstacle crossing performance revealed that they had significantly slower gait speed, smaller hip flexion angles, and larger knee adduction angles of the trailing limb, significantly larger mediolateral (ML) COM displacement and COM-COP separation distance, and significantly higher peak EMG ratios of the adductor longus, gluteus medius, and tensor fasciae latae (p < 0.05) than the healthy participants. Following the 12-week TC intervention, the PD participants had significantly increased crossing stride length, significantly decreased ML COM-COP separation (p < 0.05) and significantly increased AP COM displacement (p < 0.05), and increased EMG activity of the tibialis anterior in the leading and trailing limbs during obstacle crossing, whereas the activity of the gluteus medius and adductor longus in the leading limb decreased (p < 0.05). Moreover, the significant differences in the EMG of the gluteus medius and tensor fasciae latae muscles between PD and healthy participants found in pre-test were no longer present. After the TC intervention, the PD participants significantly improved their performance on the TUG test (p = 0.002). Therefore, people with early-stage PD presented changed gait and postural stability as well as changed neuromuscular activity of the lower limb. The 12-week online biomechanical-based TC intervention improved their gait and postural stability, particularly dynamic postural stability as measured by the COM-COP separation in people with early-stage PD. Compared to walking, performing the TC movements involved larger changes in the lower limb angles, range of motion, and higher muscle activity, particularly in the hip abductors and adductors. These characteristics of the TC movements could provide training to strengthen the muscles and improve the range of motion of the lower limbs. The gait and postural stability improvements following TC intervention are consistent with the neuromuscular activity changes in gluteus medius, tensor fasciae latae, and adductor longus muscles, indicating the mechanisms of TC training. The 12-week online biomechanical-based TC intervention program helped to decrease the ML COM-COP separation distance and could be used for the management of PD in the early stages of this condition.

La recherche d’une locomotion performante sur des terrains accidentés constitue encore à l’heure actuelle un défi pour les systèmes robotisés de toutes sortes s’y attelant. Les robots hybrides de type “roues-pattes”, qui tentent d’allier l’efficacité énergétique des roues à l’agilité des pattes, en sont un exemple aux capacités potentiellement très prometteuses. Malheureusement, le contrôle de telles structures s’avère rapidement problématique du fait des redondances cinématiques, mais aussi et surtout de la difficulté que pose la connaissance exacte de la géométrie du sol à mesure que le robot avance. Cette thèse propose alors une réponse à la complexité des systèmes roulants reconfigurables par une approche synergique entre compliance et actionnement. Pour cela, nous proposons d’exploiter une décomposition idéalement orthogonale entre les différentes formes de compliances qui réalisent la suspension du robot. Ainsi, l’actionnement au sein de la structure est ici dédié à un contrôle des efforts verticaux s’exerçant sur les roues, tandis que les déplacements horizontaux de ces dernières sont le fait d’une raideur passive combinée à une modulation locale des vitesses d’entraînement. La posture du robot est maîtrisée via l’asservissement des forces verticales fournies par un actionnement de type série-élastique. Ceci permet de garantir une adaptation spontanée de la hauteur des roues tout en conservant l’ascendant sur la distribution de la charge. La faisabilité d’un tel système de locomotion est validée à travers un prototype reposant sur quatre “roues-pattes” compliantes. Celui-ci, entièrement conçu dans le cadre de cette étude, approche la décomposition fonctionnelle proposée tout en répondant aux contraintes de réalisation et de robustesse. Tirant parti de la décomposition fonctionnelle proposée pour la structure, deux procédés de commande sont présentés afin de réaliser le franchissement des obstacles : le premier vise à exploiter l’inertie du châssis pour réaliser une modification locale des forces verticales appliquées aux roues, tandis que le second est basé sur la sélection d’un mode de répartition des efforts adaptés à la poursuite d’une évolution quasi-statique en toutes circonstances. Pour cette dernière commande, deux méthodes de synthèse sont abordées : l’une via un algorithme d’apprentissage de type “Q-learning” et l’autre par détermination de règles expertes paramétrées. Ces commandes, validées par des simulations dynamiques dans des situations variées, se basent exclusivement sur des données proprioceptives accessibles immédiatement par la mesure des variables articulaires de la structure. De cette manière, le robot réagit directement au contact des obstacles, sans avoir besoin de connaître à l’avance la géométrie du sol. / Performing an efficient locomotion on rough terrains is still a challenge for robotic systems of all kinds. “Wheel-on-leg” robots that try to combine energy efficiency of wheels with leg agility are an example with potentially very promising capabilities. Unfortunately, control of such structures turns out to be problematic because of the kinematic redundanciesand, above all, the difficulty of precisely evaluating the ground geometry as the robot advances. This thesis proposes a solution to the complexity of reconfigurable rolling systems by a synergic approach between compliance and actuation.To this purpose, we propose to exploit an ideally orthogonal decomposition between the different movements enabled by the robot suspension due to compliant elements. Then, the structure actuation is here dedicated to controlling the vertical forces applied on wheels, while the horizontal wheel displacements are due to a passive stiffness combined with a local modulation of wheel speed. The robot posture is controlled through the vertical forces servoing provided by a series elastic actuation. This ensures a spontaneous adaptation of wheel heights while keeping the control on load distribution. The feasibility of such a locomotion system is validated through a prototype based on four compliant “wheel-legs”. Entirely conceived as part of this study, this one approximates the proposed functional decomposition while meeting the realization and robustness constraints. We also present two control methods that take advantage of the functional decompositionproposed for the structure in order to cross obstacles. The first one aims to exploit the chassis inertia in order to perform a local modification of the vertical forces applied on wheels, while the second one is based on the selection of proper ways of distributing forces in order to be able to pursue a quasi-static advance in all circumstances. Two approaches are given for the production of the last control : either with a “Q-learning” algorithm or by determining parameterized expert rules. Validated by dynamic simulations in various situations, these controls rely only on proprioceptive data immediately provided by the measurement of articular variables. This way, the robot directly reacts when it touches obstacles, without having to know the ground geometry in advance.

Visual cues have previously been classified as visual exproprioceptive, when defining the relative position of the body within the environment and are continuously updated while moving (online), and visual exteroceptive when describing static features of the environment which are typically elaborated offline (feedforward). However peripheral visual cues involved in the control of movement have not previously been clearly defined using this classification. Hence the role played by peripheral visual cues in the planning and/or online control of movement remains unclear. The aim of this thesis was to provide a systematic understanding of the importance of peripheral visual cues in several types of movement, namely overground locomotion, adaptive gait, postural stability and reaching and grasping. 3D motion capture techniques were used to collect limb and whole body kinematics during such movements. Visual peripheral cues were manipulated by visual field occlusion conditions or by the employment of point-lights in a dark room. Results showed that the visual cues provided by different parts of the peripheral visual field are mainly used for online fine tuning of limb trajectory towards a target (either a floor-based obstacle or an object to grasp). The absence of peripheral visual cues while moving disrupted the spatio-temporal dynamic relationship between subject and target and resulted in increased margins of safety between body and target and increased time and variability of several dependent measures. These findings argue in favour of the classification of peripheral visual cues as visual exproprioceptive.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Aging is associated with several changes in human body functions and structures. Neuromuscular, mechanical and cognitive deficits may increase difficulties in locomotion, especially under challenging situations as the gait over obstacles. Such effects can be enforced during situations of dual-task. Limitations for mobility, strength asymmetries and decreased ability of response for changes in the context can affect the gait and increase risks for falling in the elderly. Although physical exercise benefits general health condition, its influence on performance of perturbed gait has been briefly addressed. While the usual gait can be benefited by regular physical exercise, questions still open on how regular exercise contributes to the performance of perturbed gait combined or not with a dual-task, which bring additional cognitive loading to the elderly. The purpose of this study was to evaluate the biomechanics of gait crossing a obstacle while performing or not a dual-task in sedentary and physically active elderly. Elderly aged 60 years old or more participated in the study. They were classified as sedentary or physically active. A brief interview was performed, followed by examination of cognitive status, leg preference and gait kinematics under three conditions: during the usual overground gait, overground gait crossing an obstacle and during overground gait crossing an obstacle while performing a dual-task. Results suggest that some kinematic variables of aged gait are improved in the physical active elderly, even with the execution of a dual-task. Physically active elderly seemed to adopt a more secure pattern of locomotion while crossing over an obstacle, despite of gait asymmetries observed for both the groups. / O envelhecimento acarreta modificações em diversas estruturas e funções corporais. Déficits na capacidade neuromuscular, mecânica e cognitiva podem levar a uma redução na capacidade de locomoção e dificultar a marcha em condições desafiadoras, como na presença de obstáculos. Tais efeitos podem ser aplicados em situações de dupla tarefa. Limitações na mobilidade, assimetrias na força de membros inferiores e menor capacidade de resposta a mudanças no contexto da tarefa podem afetar a marcha e aumentar o risco de quedas em idosos. Embora o exercício físico apresente uma série de benefícios para a qualidade de vida em idosos, sua influência sobre o desempenho na marcha com perturbações tem sido pouco investigada. Enquanto a marcha usual pode ser aprimorada pelo exercício regular, não se sabe como o exercício regular contribui para o desempenho na marcha em diferentes condições de perturbação onde cargas cognitivas adicionais também estão envolvidas. O objetivo deste trabalho foi avaliar a biomecânica da marcha com obstáculo e dupla tarefa em idosas sedentárias e fisicamente ativas. Participaram do estudo mulheres com idade de 60 anos ou mais, que foram classificadas como fisicamente ativas ou sedentárias. Após a realização de uma anamnese, as idosas foram avaliadas quanto ao estado mental, preferência lateral e cinemática da marcha em três situações: durante a marcha normal, livre de obstáculo; durante a transposição de um obstáculo; e durante a transposição de um obstáculo concomitante à realização de uma tarefa cognitiva secundária. Os principais resultados sugerem que algumas variáveis da marcha com obstáculo são beneficiadas pela prática do exercício regular, mesmo com a realização de uma dupla tarefa. Idosas fisicamente ativas parecem assumir padrões mais seguros de marcha para cruzar um obstáculo, ainda que assimetrias ocorram para ambos os grupos.

Visual cues have previously been classified as visual exproprioceptive, when defining the relative position of the body within the environment and are continuously updated while moving (online), and visual exteroceptive when describing static features of the environment which are typically elaborated offline (feedforward). However peripheral visual cues involved in the control of movement have not previously been clearly defined using this classification. Hence the role played by peripheral visual cues in the planning and/or online control of movement remains unclear. The aim of this thesis was to provide a systematic understanding of the importance of peripheral visual cues in several types of movement, namely overground locomotion, adaptive gait, postural stability and reaching and grasping. 3D motion capture techniques were used to collect limb and whole body kinematics during such movements. Visual peripheral cues were manipulated by visual field occlusion conditions or by the employment of point-lights in a dark room. Results showed that the visual cues provided by different parts of the peripheral visual field are mainly used for online fine tuning of limb trajectory towards a target (either a floor-based obstacle or an object to grasp). The absence of peripheral visual cues while moving disrupted the spatio-temporal dynamic relationship between subject and target and resulted in increased margins of safety between body and target and increased time and variability of several dependent measures. These findings argue in favour of the classification of peripheral visual cues as visual exproprioceptive.