The overall objective of this thesis was to compare compensatory reactions in young and older adults following unexpected platform perturbations in the frontal and sagittal planes during gait. Eleven young (aged 18-30) and ten community-dwelling older adults (aged 65+) completed a general health questionnaire, Mini BESTest, hip strength tests, and 45 walking trials on a motion platform. The walking trials were completed in a randomized block design on a 5 m pathway that moved following right heel contact after at least two steps. Young adults had stronger hips and performed better on the Mini BESTest than older adults. Compensatory reactions (measured through gait parameters and centre of mass motion) indicated that lateral perturbations were more difficult for both groups. These measures showed that young adults were able to recover more quickly than older adults. This could be attributed to altered base of support changes that occurred immediately following platform motions. / Ontario Graduate Scholarship

Made available in DSpace on 2016-12-12T17:32:57Z (GMT). No. of bitstreams: 1 Resumo Josilene.pdf: 200186 bytes, checksum: 2f7be00775cd12b3c58b24e75d73a884 (MD5) Previous issue date: 2014-06-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study aimed to investigate the effect of balance perturbation training on the strategies of postural control in subjects with chronic ankle instability (CAI). Forty-four subjects with CAI were randomly assigned in the training group (TG, n=22) and control group (CG, n=22). The TG performed a single session of balance training (25 minutes) involving a task of kicking a ball in single-leg stance. CG received no intervention. The primary outcomes were tested during the kicking a ball (dynamic) and quietly standing on single-leg (static) tasks. The primary outcome was the sum of the integral electromyographic (Σ∫EMG) of the supporting leg lower limb muscles. The Σ∫EMG were calculated during the intervals typical for anticipatory and compensatory adjustments. Secondary outcomes were: the integral electromiographic of the lower limb muscles individually and the displacement of center of pressure (COP) during similar intervals. The primary outcome measures were not significantly different between groups. The magnitude of Σ∫EMG, however, was lower in the post-training compared to pre-training only for the TG during the compensatory adjustment, i.e., the time interval that followed the leg movement. Consequently there was a significant increase in the COP displacement area after training during the dynamic task. In contrast, the COP excursion decreased after training of during the static task. A single session of balance perturbation training may promote changes in postural control strategies in subjects with CAI. Particularly, reducing the compensatory activity of the specific muscle groups and increasing postural sway during dynamic task. Although differences between groups were not observed, these results should stimulate new and more comprehensive studies to investigate the effect of balance perturbation trainings in individuals with CAI. / O presente estudo objetivou investigar os efeitos do treino de equilíbrio mediante perturbações sobre as estratégias de controle postural em indivíduos com instabilidade crônica do tornozelo (ICT). Quarenta e quatro indivíduos com ICT foram aleatorizados no grupo treino (GT; n = 22) e grupo controle (GC; n = 22). O GT realizou uma única sessão de treino de equilíbrio (25 minutos) que envolveu a tarefa de chutar uma bola em apoio unipodal. O GC não recebeu a intervenção. As medidas de desfecho primário e secundário foram testadas durante a tarefa de chutar uma bola em apoio unipodal (dinâmica) e na postura unipodal quieta (estática). O desfecho primário foi à soma da integral eletromiográfica (Σ∫EMG) dos músculos do membro inferior de apoio durante a tarefa dinâmica. As Σ∫EMG foram calculadas nos intervalos de tempo típicos para os ajustes antecipatórios e compensatórios. Os desfechos secundários foram: as integrais eletromiográficas dos músculos analisados individualmente e a área do deslocamento do centro de pressão corporal (COP) durante intervalos de tempo similares. A medida de desfecho primário não foi significante entre os grupos. Entretanto, a magnitude da Σ∫EMG dos músculos posteriores do membro inferior foi menor no pós-treino quando comparado ao pré-treino somente para o GT durante os ajustes compensatórios, i.e., o intervalo de tempo que sucedeu o início do movimento da perna. Consequentemente, houve um aumento significante da área do deslocamento do COP após o treino durante a tarefa dinâmica. Em contraste, a excursão do COP diminuiu após o treino durante a tarefa estática. Uma única sessão de treino de equilíbrio pode promover modificações nas estratégias de controle postural em indivíduos com ICT. Particularmente, diminuindo a atividade compensatória de grupos musculares específicos e aumentando a oscilação postural durante a tarefa dinâmica. Embora não observadas diferenças entre grupos, esses resultados devem impulsionar novos estudos a fim de investigar os efeitos dos treinos que usam perturbações posturais em indivíduos com ICT.

La chute chez les seniors constitue un problème de santé publique. Citée comme la seconde cause de décès accidentel dans le monde, elle concerne un tiers des Français de plus de 65 ans. Les séquelles physiques et fonctionnelles qui en résultent, les conséquences psychosociales nuisibles pour la qualité de la vie, la perte d’autonomie et son coût de prise en charge justifient l’attention qui lui est actuellement portée. Du point de vue du chercheur, les interprétations sous-jacentes à la surexposition des personnes âgées au risque de chute restent controversées, notamment parce que la compréhension de la coordination dynamique corporelle et de l’implication corticale lors du contrôle de l’équilibre est encore limitée. L’étude de la chute et des mécanismes qui y conduisent présente donc un double intérêt, fondamental et sociétal. Une chute survient si deux conditions sont réunies. La première est la perte initiale de l’équilibre, un ‘pré-requis’ qui peut toucher la population entière dans son quotidien. La seconde est un échec des mécanismes de rééquilibration, c’est à dire de la stratégie de réponse mise en œuvre pour compenser la déstabilisation : comment s’opère la sélection d’une stratégie de rattrapage, à partir de quelle appréciation du contexte et des informations sensorielles disponibles est-elle choisie ? qu’est ce qui assure son opérationnalité et garantit le rattrapage ou signe au contraire son échec ?...Pour répondre à ces questions, nous nous sommes donc intéressés à ce moment critique où il est encore possible de modifier l’issue finale par des ajustements posturaux et des actions motrices rapides et adéquats chez une population de jeunes adultes. La première étude est une analyse globale de la phase précoce d’une chute -abrégée par un harnais- (soit quelques centaines de millisecondes après la perturbation), afin d’évaluer la capacité du sujet à réagir à une perturbation imprévue et de développer des stratégies garantissant une protection efficace. Cette première étape se propose d’identifier les indicateurs discriminants et prédictifs d’une chute et d’un rattrapage au niveau neurophysiologique et biomécanique. Cette étude a également permis de mettre en évidence la présence d’un délai temporel incompressible appelé « phase passive », source de contraintes spatio-temporelles à l’expression complète d’une réponse posturale adaptée. Dans la seconde étude, de modélisation, nous avons élaboré un modèle mécanique personnalisé, construit à partir de radiographies tridimensionnelles non invasives du corps entier. Cette modélisation nous a permis d’analyser la contribution relative de propriétés biomécaniques passives et des synergies musculaires actives en jeu pendant les perturbations récupérables de l’équilibre ou non en comparant les résultats expérimentaux (‘réels’) obtenus à l’aide d’un dispositif asservi pour provoquer des chutes de plain-pied et la réponse théorique prédite (‘simulée’) à l’aide du modèle. Les résultats obtenus permettent de confirmer que le comportement du corps est en phase précoce-dicté par ses propriétés mécaniques, et peut être assimilé à un modèle simplifié. Après avoir mis en évidence l’existence d’une phase inertielle d’une durée équivalente à la moitié du temps disponible avant l’impact, notre questionnement s’est orienté vers le traitement de l’information en-cours lors de cette phase afin d’évaluer la contribution corticale alors que la réponse posturale évolue. La troisième étude consiste principalement à appréhender la charge cognitive impliquée dans le contrôle sensori-moteur, en particulier lors d’une chute, à l’aide du paradigme de double-tâche. En conclusion, à travers une approche pluridisciplinaire, les résultats obtenus dans cette thèse permettent d’émettre des recommandations intéressantes pour une prévention et une rééducation adaptée dans le but de contribuer à l’amélioration de la qualité de vie des personnes âgées. / A better understanding of what happens during an unintentional fall is relevant in preventing their occurrence. A fall is due to a failure of compensatory reactions to recover from postural perturbations during the descent phase which starts at the subject loss of balance point and lasts no more than 700-1000milliseconds [Hsiao, 1998]. The aim of the first study was to compare the biomechanical and muscular behavior during the pre-impact phase during non-recoverable falls and successful recovery trials. The experimental study aimed to evaluate the subject’s ability to distinguish in the first 500 milliseconds following the onset of perturbation a low-threatening perturbation from a high challenging one and can then predict the scenario that will more likely lead to a fall using specific motor strategies. In such a challenging task, we hypothesized that the constraints imposed by the biomechanical properties ultimately determine the ability to trigger efficient muscle activities. Full body 3D kinematics and associated muscle activities were collected in 30 young healthy subjects during fast and slow unpredictable multidirectional support-surface translations. 40 cm support-surface translations were used to evoke the balancing reactions (0,35 vs 0,9 m/s during resp. 1000 vs 500 millisecond The perturbation velocities were selected so that successful recovery should occur in milder trials whereas fast trials were sufficiently challenging to trigger non-recoverable falls. Analyses focused on the spatial and temporal characteristics of the Centre of Mass, angle variations, recovery step characteristics, and EMG activities (onset latencies and amplitudes) across each trial and muscle. Moreover, a 17-segment numerical and personalized model was created, based on stereoradiographic head to feet X-ray images followed by 3D-reconstruction methods to assess subject-specific geometry and inertial parameters. The outputs resulting from simulated falls allowed us to discard the contributions of the passive (inertia-induced) versus the active mechanisms (feedback-controlled and time-delayed neuromuscular components) of the response. The first outcome of that study was that the fall could be divided in distinct phases. For about 200 milliseconds following the onset of platform translation, the head remained stable in space. Similarly, the comparison with the simulated data supported that the CoM displacement matched the subject-dependant mechanical model. During a second phase of the fall, despite the fact that automated muscle postural synergies started at 80 milliseconds after perturbation onset, the trajectory of the body appeared to be exclusively dictated by its biomechanical properties. Later, muscle activities influenced the body trajectories, which consequently differed on a trial-to-trial basis. The simulation was in good agreement with the experimental results. The specificity of the postural response resulting in a strategy chosen to avoid a fall thus appeared in a late-phase, which can be explained because during a fall, the subjects had to prepare to the impact on the basis of sensory information that were not redundant but available in a sequential order: proprioceptive information appearing first while vestibular and visual information continued to signal a stabilized head in space. The sole proprioceptive information would be insufficient to trigger rapid and appropriate postural response. Moreover, in accordance with our results suggesting the importance of the late-phase and on-line controlled responses, a long inertial passive phase in the fast trials does not allow a large spatiotemporal window for compensatory reactions to occur. These could not only depend on the previously described automated postural synergies because the time constraints imposed by biomechanics permit in principle volitional motricity to play an important role very early in the fall. (...)