Examination of goal-directed aiming tasks has revealed that rapid, discrete human action is amendable to online control. This control affords humans a margin of error in movement planning and execution as well as a means of acquiring their goals when the body and/or the environment are extrinsically perturbed. For over a century, the models of online movement control that have best described the trajectories and outcomes of goal-directed reaches hold that these movements are composed of two distinct components. The first component moves the limb from its resting position towards the target. The second component is a corrective movement that is formed on the basis of a visual referencing of the moving limb and target positions. As such, the temporal and spatial characteristics of these discrete movement changes have been attributed to the limits of visual information processing. Furthermore, the absence of any discrete movement changes in the portions of movements outside of the temporal and spatial limits of vision led many investigators to conclude that first component impulses are ballistic and uncontrollable. However, recent studies involving environmental perturbation and within-subject trial-to-trial spatial variability analyses have evidenced that initial impulses are privy to online control. Because the corrections made early in movement impulses occur quicker than purely afferent visual information can be processed this form of control has been attributed to the use of forward anticipatory processes. The four studies presented here examine the nature of initial impulse control through kinematic analyses of reaches made to targets against various combinations of limb, target, and environment perturbations. This was done in order to evaluate anticipatory control's relationship with visually-regulated control and the relative influence the two processes have on the movement trajectory and performance outcome. The first study examined target-directed reaches made against illusory moving background and target relocation perturbations. The results showed the presence of early anticipatory and late visually-regulated control. Non-interactive main effects of the two perturbations on outcome accuracy revealed that the processes operate independently. The second study tested the applicability of an air discharging stylus as a tool for perturbing reach velocities. The results showed that the stylus effectively perturbed limb velocity and highlighted the presence of a limb forwarding response to either an advancing or hindering perturbation. The findings evidence the non-specific nature of anticipatory control responses. The third study examined reaches made against combinations of actual limb velocity and target position perturbations. The interactive effect of the two perturbations on reach trajectories and outcome accuracy indicated that the perturbations were salient enough to prompt parallel operation of the two control processes. Again, the control of initial movement portions was highlighted by non-specific responses to the perturbations. The fourth study examined reaches made against combinations of illusory and actual perturbations to both the anticipatory and visually-regulated control processes. Interestingly, performers withheld responses to the illusory perturbation unless they were also responding to an actual perturbation. This finding suggests that anticipatory control responses are biased during movement preparation. Furthermore, combined illusory and actual perturbations to target position had interactive effects on visually regulated control. Overall, the studies evidence that target-directed movements are mediated by two modes of control. There is an anticipatory mode of control that operates continuously and, given that reaches are made within the spatial and temporal limits of visual processing, there is also a feedback driven discrete mode of control that overlaps with the continuous mode. / Thesis / Doctor of Philosophy (PhD)

Propulsionar cadeira de rodas (CR) está relacionado a altas incidências de dores e lesões em usuários de cadeira de rodas (UCR). Embora seja reconhecida como uma forma de baixa eficiência para se locomover, representa fundamental importância para o desempenho dessas pessoas nas atividades de vida diária, ocupacionais, de lazer e em sua participação social. Ao longo dos estudos sobre a propulsão nas últimas décadas, foi notado recentemente em especial, que a propulsão inicial que retira o sistema usuário-cadeira de rodas do repouso, o colocando em movimento, apresentam a maiores solicitações mecânicas. Considerando que esta situação é executada várias vezes durante o uso típico da cadeira de rodas, torna-a relevante objeto de estudo. Como até o momento, pouco foram os estudos sobre a fase inicial da autopropulsão e que do ponto de vista da neuroativação, esse movimento não foi abordado, este estudo tem como objetivo descrever o gesto da fase inicial da autopropulsão de cadeira de rodas manual de UCR, por meio da eletromiografia, apresentando os níveis atingidos de ativação muscular e o perfil do comportamento de ativação ao longo da execução do gesto da autopropulsão. Para isso foram avaliados oito grupos musculares envolvidos nesse gesto de onze UCR. Os sinais eletromiográficos foram coletados dos oito grupos musculares, simultaneamente, durante a execução de dez propulsões, partindo do repouso, de cada UCR participante da pesquisa. Com relação aos níveis de ativações musculares, foi introduzido um método alternativo de normalização. Esse método consiste na realização do teste de contração isométrica máxima na própria CR. Os resultados foram apresentados em boxplot a fim de demonstrar o pico de ativação bem como a distribuição dos demais níveis de ativação. Como o novo método proposto demonstrou limitações, inviabilizou a interpretação dos resultados quanto as intensidades calculadas. Sobre o perfil de acionamento muscular ao longo da execução da autopropulsão, os resultados foram expostos em gráficos normalizados pelo pico dinâmico e em relação ao período de um ciclo de propulsão, evidenciando o comportamento ativado em cada instante do ciclo. Segundo os resultados dessa segunda metodologia, entre os oito grupos musculares examinados, os que apresentaram os maiores picos de ativação foram: deltoide anterior (80,27%), o peitoral maior (79,27%), os flexores de punho (78,93%) e os extensores de punho (80,65%). Os achados colaboram com estudos anteriores de outros autores de que os principais grupos musculares efetores na propulsão de CR são o deltóide anterior (DA) e peitoral maior (PM). / Propelling wheelchair (CR) is related to high incidences of pain and injury in wheelchair users (WCU). Although this locomotion way be known as low efficient locomotion mode, it represents fundamental importance for these people performance in daily living activities, occupational, leisure and in their social participation. Over the studies course on propulsion in recent decades, it has recently been noted, particularly, that the initial stage of wheelchair propulsion which retires the user-wheelchair system from resting, putting it into motion, presents greater mechanical stresses. It considering this situation is executed several times during the typical wheelchair usage, it makes this relevant study object. As until current moment, there are few studies about initial stage of wheelchair propulsion and, from the neuroactivation point of view, this movement was not approached, this study aims to describe the gesture of initial stage of manual wheelchair propulsion from WCU, across electromyography, presenting the muscular activation levels achieved and the recruited behavior profile during the propulsion gesture execution. For this problem, eight muscle groups involved in this gesture were evaluated from eleven WCU. Electromyographic signals were collected from these eight muscle groups, simultaneously, during ten propulsions execution, starting from resting, of each WCU participant of the research. Regarding the muscular activation levels, an alternative normalization method was introduced. This method consists in performing the maximum isometric contraction test on the wheelchair itself. The results were showed in boxplot in order to demonstrate the activation peak as well as the remaining activation levels distribution. As the new method proposed showed limitations, a better results interpretation was not possible on calculated intensities. Regarding the muscular activation profile during the propulsion execution, the results were exposed in graphs normalized by the dynamic peak as well as in relation to a single propulsion cycle, evidencing the activated behavior at each cycle moment. According to the results based on second methodology, among the eight muscle groups examined, the ones which presented the highest activation peaks values were: the anterior deltoid (80.27%), the pectoralis major (79.27%), the wrist flexors (78, 93%) and the wrist extensors (80.65%). The findings agree with previous studies by other authors that the main effector muscle groups in CR propulsion are anterior deltoid (DA) and pectoralis major (PM).

Propulsionar cadeira de rodas (CR) está relacionado a altas incidências de dores e lesões em usuários de cadeira de rodas (UCR). Embora seja reconhecida como uma forma de baixa eficiência para se locomover, representa fundamental importância para o desempenho dessas pessoas nas atividades de vida diária, ocupacionais, de lazer e em sua participação social. Ao longo dos estudos sobre a propulsão nas últimas décadas, foi notado recentemente em especial, que a propulsão inicial que retira o sistema usuário-cadeira de rodas do repouso, o colocando em movimento, apresentam a maiores solicitações mecânicas. Considerando que esta situação é executada várias vezes durante o uso típico da cadeira de rodas, torna-a relevante objeto de estudo. Como até o momento, pouco foram os estudos sobre a fase inicial da autopropulsão e que do ponto de vista da neuroativação, esse movimento não foi abordado, este estudo tem como objetivo descrever o gesto da fase inicial da autopropulsão de cadeira de rodas manual de UCR, por meio da eletromiografia, apresentando os níveis atingidos de ativação muscular e o perfil do comportamento de ativação ao longo da execução do gesto da autopropulsão. Para isso foram avaliados oito grupos musculares envolvidos nesse gesto de onze UCR. Os sinais eletromiográficos foram coletados dos oito grupos musculares, simultaneamente, durante a execução de dez propulsões, partindo do repouso, de cada UCR participante da pesquisa. Com relação aos níveis de ativações musculares, foi introduzido um método alternativo de normalização. Esse método consiste na realização do teste de contração isométrica máxima na própria CR. Os resultados foram apresentados em boxplot a fim de demonstrar o pico de ativação bem como a distribuição dos demais níveis de ativação. Como o novo método proposto demonstrou limitações, inviabilizou a interpretação dos resultados quanto as intensidades calculadas. Sobre o perfil de acionamento muscular ao longo da execução da autopropulsão, os resultados foram expostos em gráficos normalizados pelo pico dinâmico e em relação ao período de um ciclo de propulsão, evidenciando o comportamento ativado em cada instante do ciclo. Segundo os resultados dessa segunda metodologia, entre os oito grupos musculares examinados, os que apresentaram os maiores picos de ativação foram: deltoide anterior (80,27%), o peitoral maior (79,27%), os flexores de punho (78,93%) e os extensores de punho (80,65%). Os achados colaboram com estudos anteriores de outros autores de que os principais grupos musculares efetores na propulsão de CR são o deltóide anterior (DA) e peitoral maior (PM). / Propelling wheelchair (CR) is related to high incidences of pain and injury in wheelchair users (WCU). Although this locomotion way be known as low efficient locomotion mode, it represents fundamental importance for these people performance in daily living activities, occupational, leisure and in their social participation. Over the studies course on propulsion in recent decades, it has recently been noted, particularly, that the initial stage of wheelchair propulsion which retires the user-wheelchair system from resting, putting it into motion, presents greater mechanical stresses. It considering this situation is executed several times during the typical wheelchair usage, it makes this relevant study object. As until current moment, there are few studies about initial stage of wheelchair propulsion and, from the neuroactivation point of view, this movement was not approached, this study aims to describe the gesture of initial stage of manual wheelchair propulsion from WCU, across electromyography, presenting the muscular activation levels achieved and the recruited behavior profile during the propulsion gesture execution. For this problem, eight muscle groups involved in this gesture were evaluated from eleven WCU. Electromyographic signals were collected from these eight muscle groups, simultaneously, during ten propulsions execution, starting from resting, of each WCU participant of the research. Regarding the muscular activation levels, an alternative normalization method was introduced. This method consists in performing the maximum isometric contraction test on the wheelchair itself. The results were showed in boxplot in order to demonstrate the activation peak as well as the remaining activation levels distribution. As the new method proposed showed limitations, a better results interpretation was not possible on calculated intensities. Regarding the muscular activation profile during the propulsion execution, the results were exposed in graphs normalized by the dynamic peak as well as in relation to a single propulsion cycle, evidencing the activated behavior at each cycle moment. According to the results based on second methodology, among the eight muscle groups examined, the ones which presented the highest activation peaks values were: the anterior deltoid (80.27%), the pectoralis major (79.27%), the wrist flexors (78, 93%) and the wrist extensors (80.65%). The findings agree with previous studies by other authors that the main effector muscle groups in CR propulsion are anterior deltoid (DA) and pectoralis major (PM).