Maintaining postural control in standing requires the center of mass (COM) to be kept within the boundaries of the base of support (BOS). As the COM moves to a region outside the BOS, a step is often required, increasing the risk of falling, and therefore injury. All too often, humans are subjected to different perturbations while maintaining upright stance, and so to control the COM in these situations, postural activity through musculature at the ankle, knee, and hip are recruited according to demand associated with the level of perturbation. It is also believed that control of the head allows components of the visual and vestibular systems to contribute stable reference values. In order to understand human response to, and in preparation for perturbation, researchers have employed a number of experimental techniques, including i) loading and subsequent unloading of body segments such as the arm or leg; ii) single discrete platform movements; and iii) continuous platform movements. While many studies have focussed on examining postural control mechanisms during discrete perturbations in children and adolescents, these mechanisms in response to continual perturbation have not been well documented in observable developmental stages of youth, nor have they been well documented in special populations. Therefore, the primary aim of this doctoral dissertation was to characterize the reactive and anticipatory postural control mechanisms in children and adolescents, as well as to examine and characterize them in the Cerebral Palsy population. To achieve this overarching goal, three separate studies were performed. The first study characterized the anticipatory and reactive mechanisms of postural control in typically developing children aged 7 to 17 years. Specifically, postural muscle activity in the lower limbs, an index of head anchoring strategy, and body segment cross-correlations were characterized in response to, and in anticipation of, continuous platform oscillation movement at various frequencies. The second experiment characterized these same mechanisms in children of similar ages with cerebral palsy, and compared the results to those found in the first study. The results of these studies indicated a slight shift to anticipatory measures after repeated exposure to a specific frequency of platform oscillation, however, each transition to a greater platform speed resulted in more conservative measures of postural control. Furthermore, youth with cerebral palsy tended to control their posture much in the same way of typically developing children and adolescents under less challenging conditions however, with the increased difficulty associated with higher frequency oscillation were not able to generate adequate postural responses. The final study in this dissertation investigated the effects of a one-week intensive virtual reality-based exercise programme. In this study, postural control mechanisms were observed before and after a one-week time period, during which half of the participants received the enhanced exercise while the remaining participants received no treatment at all. The results from this study indicated there was no effect of a 5-day VR-based intervention on postural control mechanisms used in response to oscillating platform perturbations. Taken together, the results from these studies extend the current understanding of reactive and anticipatory mechanisms of postural control in children and adolescents, both typically developing and those with cerebral palsy.

Estudos prévios têm indicado que o aumento da demanda de estabilidade manual induz maior estabilidade do equilíbrio corporal no controle das posturas quieta e perturbada. O presente estudo teve por objetivo avaliar o efeito da demanda de estabilidade imposta por uma tarefa manual sobre a regulação postural dinâmica em função da frequência de oscilação da base de suporte. Participaram desse estudo 20 estudantes universitários de ambos os sexos. A tarefa consistiu em manter um cilindro o mais estável possível sobre uma bandeja enquanto o equilíbrio em postura ereta era mantido em translações sinusoidais contínuas da plataforma móvel por 1 min., nas frequências de 0,4 Hz (baixa) ou 1 Hz (alta). A demanda de estabilidade manual foi manipulada por meio da disposição do cilindro. Na condição chamada de alta restrição (AR), o cilindro foi apoiado sobre sua face circular; na condição chamada de baixa restrição (BR), o cilindro foi apoiado sobre sua face plana. Os resultados mostraram que AR induziu menores amplitudes de oscilações de cabeça, centro de massa e bandeja na frequência de 0,4 Hz, porém não na frequência de 1 Hz. A análise das variáveis de coordenação revelou que na frequência de 0,4 Hz, AR levou a maiores valores de fase relativa entre as rotações cíclicas de tornozelo-quadril e tornozelo-ombro, como também na coordenação entre CM-plataforma e CP-plataforma. As análises mostraram que a condição de alta restrição também afetou o controle postural e manual na frequência de oscilação de 1 Hz, com aumento da amplitude de oscilação de CP e de rotações do ombro. Estes resultados sugerem que o controle postural dinâmico é regulado em diferentes parâmetros de maneira integrada e flexível, com interação recíproca entre os componentes da tarefa manual e postural, para atender à demanda de estabilidade imposta por uma tarefa posturomanual / Previous studies have indicated that increased steadiness constraints given by a manual task leads to gains of postural stability in quiet and perturbed standing. The aim of the present study was to evaluate the effects of manual task constraints on the regulation of dynamic postural control according to the frequency of sinusoidal translations of the base of support. Twenty university students performed a dual posturomanual task consisting of maintaining a cylinder on a handheld tray as stable as possible while maintaining the dynamic upright balance on a platform oscillating in sinusoidal translations at 0.4 Hz (low) or 1 Hz (high) frequencies during intervals of 1 min. The effects of manual task were studied through the manipulation of task constraint conditions set by positioning the cylinder supported on its round or flat side, corresponding respectively to high (HC) and low (LC) manual task constraints. Results showed that HC led to reduced oscillation amplitudes of the head, center of mass, and tray at 0.4 Hz, but not at 1 Hz. The coordination variables indicated that at 0.4 Hz, HC led to increased relative phase values between ankle-shoulder and hip-shoulder rotations, as also between center of mass-feet and center of pressure-feet oscillations in the slow oscillation frequency. Further analyses showed that the high manual task constraint also affected variables related to both postural and manual task components at 1 Hz, with increased center of pressure and shoulder rotation amplitudes of oscillation. These results suggest that dynamic postural control is regulated through different parameters in a flexible and integrated way in order to attend the stability demands imposed by a posturomanual task

Estudos prévios têm indicado que o aumento da demanda de estabilidade manual induz maior estabilidade do equilíbrio corporal no controle das posturas quieta e perturbada. O presente estudo teve por objetivo avaliar o efeito da demanda de estabilidade imposta por uma tarefa manual sobre a regulação postural dinâmica em função da frequência de oscilação da base de suporte. Participaram desse estudo 20 estudantes universitários de ambos os sexos. A tarefa consistiu em manter um cilindro o mais estável possível sobre uma bandeja enquanto o equilíbrio em postura ereta era mantido em translações sinusoidais contínuas da plataforma móvel por 1 min., nas frequências de 0,4 Hz (baixa) ou 1 Hz (alta). A demanda de estabilidade manual foi manipulada por meio da disposição do cilindro. Na condição chamada de alta restrição (AR), o cilindro foi apoiado sobre sua face circular; na condição chamada de baixa restrição (BR), o cilindro foi apoiado sobre sua face plana. Os resultados mostraram que AR induziu menores amplitudes de oscilações de cabeça, centro de massa e bandeja na frequência de 0,4 Hz, porém não na frequência de 1 Hz. A análise das variáveis de coordenação revelou que na frequência de 0,4 Hz, AR levou a maiores valores de fase relativa entre as rotações cíclicas de tornozelo-quadril e tornozelo-ombro, como também na coordenação entre CM-plataforma e CP-plataforma. As análises mostraram que a condição de alta restrição também afetou o controle postural e manual na frequência de oscilação de 1 Hz, com aumento da amplitude de oscilação de CP e de rotações do ombro. Estes resultados sugerem que o controle postural dinâmico é regulado em diferentes parâmetros de maneira integrada e flexível, com interação recíproca entre os componentes da tarefa manual e postural, para atender à demanda de estabilidade imposta por uma tarefa posturomanual / Previous studies have indicated that increased steadiness constraints given by a manual task leads to gains of postural stability in quiet and perturbed standing. The aim of the present study was to evaluate the effects of manual task constraints on the regulation of dynamic postural control according to the frequency of sinusoidal translations of the base of support. Twenty university students performed a dual posturomanual task consisting of maintaining a cylinder on a handheld tray as stable as possible while maintaining the dynamic upright balance on a platform oscillating in sinusoidal translations at 0.4 Hz (low) or 1 Hz (high) frequencies during intervals of 1 min. The effects of manual task were studied through the manipulation of task constraint conditions set by positioning the cylinder supported on its round or flat side, corresponding respectively to high (HC) and low (LC) manual task constraints. Results showed that HC led to reduced oscillation amplitudes of the head, center of mass, and tray at 0.4 Hz, but not at 1 Hz. The coordination variables indicated that at 0.4 Hz, HC led to increased relative phase values between ankle-shoulder and hip-shoulder rotations, as also between center of mass-feet and center of pressure-feet oscillations in the slow oscillation frequency. Further analyses showed that the high manual task constraint also affected variables related to both postural and manual task components at 1 Hz, with increased center of pressure and shoulder rotation amplitudes of oscillation. These results suggest that dynamic postural control is regulated through different parameters in a flexible and integrated way in order to attend the stability demands imposed by a posturomanual task