Obesity is associated with an increased risk of falls and subsequent injury. Previous studies have shown weight loss and strength training to be beneficial to balance, but knowing which is more beneficial will allow researchers to design interventions to maximize the benefits in terms of balance and reducing risk of falls. Therefore, the purpose of the first study was to evaluate the effects of weight loss and strength training on balance recovery using a combination of laboratory experiments and mathematical modeling. Nine male subjects with BMI 30.1 to 36.9 kg/m² were released from a forward lean and attempted to recover balance using an ankle strategy. Lean angle was increased until subjects required a step or hip flexion to recover balance. The maximum lean angle, θ_max, was used as the measure of balance recovery capability. Experimental data were used as inputs to an inverted pendulum model of balance recovery. Multiple simulations were used to determine the effects of strength (maximum ankle torque and ankle torque generation rate) and weight loss on θ_max. Changes in weight and strength were linearly related to changes in θ_max. A 6.6 ± 0.4% decrease in weight or 6.9 ± 0.9% increase in strength were estimated as required to improve (increase) θ_max by 1 degree. Based on these results, balance recovery using an ankle strategy can improve with either reductions in weight or increases in strength. In addition, weight loss may be a more effective intervention than strength gain at improving balance recovery capability. The purpose of the second study was to quantify changes in body segment inertial parameters (BSIPs) with weight loss. These data were needed to alter BSIPs in the first study to mimic changes with weight loss. Both before and after weight loss, magnetic resonance imaging scans were acquired along the length of the body and were used to calculate segment masses, COM positions, and radii of gyration. A number of significant changes in BSIPs occurred with weight loss. / Master of Science

Obesity is a major and growing health concern associated with an increased risk of falls. The majority of falls are thought to result from some kind of postural perturbation, yet the biomechanical mechanisms as to why obese individuals fall more often is unclear. Therefore, the goal of this study was to investigate the effects of obesity on balance recovery in response to small forward postural perturbations. Twenty male participants, including 10 lean (mean BMI ± SD: 21.9 ± 1.4) and 10 obese (BMI: 33.2 ± 2.3), were exposed to two types of postural perturbations (force impulses applied with a pendulum and angular displacements administered with a release mechanism). Participants attempted to recover balance with only an ankle strategy such that neither a step nor hip flexion was utilized. Quiet standing trials were also conducted for comparison with the literature. Obese individuals exhibited less center of mass (COM) displacement and a slower COM velocity compared to lean individuals when exposed to identical force perturbations. When exposed to the force perturbations relative to body weight, and when released from identical lean angles, no differences in COM performance were found. During quiet standing, no differences in center of pressure (COP) velocity were observed between obese and lean groups. In all tasks, the obese generated higher ankle torque than the lean. Overall, the obese participants exhibited no differences in movement or less/slower movement than the lean participants when recovering from small forward postural perturbations as well as during quiet standing. These results imply that obesity in young adult males did not impair balance recovery for the tasks investigated. / Master of Science

Obesity is associated with an increased risk of falls and subsequent injury. Most falls result from some type of postural perturbation. As such, it is important to understand how obesity influences balance recovery from a postural perturbation. There is limited information on the effects of obesity on balance recovery, and the limited available information is ambiguous. Therefore, the purpose of the research within this dissertation was to investigate the effects of obesity on balance recovery after a postural perturbation in young adults to better understand how obesity contributes to fall risk. Four separate studies make up this dissertation. The purpose of the first study was to investigate the effects of obesity on balance recovery ability using an ankle strategy in young adults. Normal-weight and obese participants recovered balance using an ankle strategy after three types of postural perturbations: an initial angular displacement, an initial angular velocity from the natural stance, and an initial angular velocity from a prescribed position. Obese participants were unable to recover balance using an ankle strategy as well as normal-weight participants when perturbations involved an initial angular velocity. However, no differences between obese and normal-weight participants were found when perturbations only involved an initial angular displacement. The effect of obesity on balance recovery in young adults was dependent on the perturbation characteristics, and may be explained by a possible beneficial effect of increased inertia on balance recovery after perturbations with little or no initial angular velocity. The purpose of the second study was to examine the effects of obesity on balance recovery by stepping in young adults. The ankle strategy has the benefit of simplifying the mechanics of balance recovery, but limits generalizability to more realistic fall scenarios where stepping to extend the base of support and recover balance is desired. Similar to the first study, participants attempted to recover balance following two types of postural perturbations: an initial angular displacement from an upright stance (by releasing participants from a static forward lean), and an initial angular velocity while in an upright stance (using a translating platform). In contrast to the first study, the ability to recover balance with a single-step did not differ between young normal-weight and obese adults. These results suggest that the reported increase in fall risk in obese adults is not a result of impaired balance recovery ability (at least among young adults that were tested here). The third study examined the effects of obesity on body kinematics immediately following a trip-like perturbation in young adults. Obesity was found to increase body angular velocity the perturbation, and that increases in body angular velocity were associated with an increased probability of a failed recovery. These results suggest that when a young obese and young normal-weight individual trip while walking at similar speeds, the young obese individual may be at a greater risk of falling following a trip because the young obese individual will experience a greater body angular velocity. This detrimental effect of obesity on the difficulty of recovering from a trip-like perturbation in young adults is most likely due to how mass is distributed throughout the body and not the amount of mass itself. The final study examined the relationship between relative strength and functional capability in young adults, and how obesity influences this relationship. To compare relative strength used during a functional task (i.e. balance recovery from a forward fall), the obese and normal-weight individual should complete the task with identical kinematics. Forward dynamic simulations were used to address this research question, instead of human subjects testing, to achieve identical kinematics. Differences in peak relative torques were found between the normal-weight and obese model, with the largest differences seen at the hip. These findings suggest that young obese individuals use greater relative strength at some joints than young normal-weight individuals to perform the time-critical task of balance recovery, and that these differences in relative strength demands may limit functional capability in young individuals who are obese. / Ph. D.

Fall related injuries are a major public health concern due to their high associated medical costs and negative impact on quality of life. Obese and older adults are reported to fall more frequently than their normal-weight and young counterparts. To help identify potential mechanisms of these falls the purpose of the research within this dissertation was to investigate the effects of obesity and age on the likelihood of tripping and subsequent balance recovery. Four experimental studies were conducted. The purpose of the first study was to investigate the effects of obesity, age and gender on the likelihood of tripping during level walking. Likelihood of tripping was assessed with median minimum foot clearance (MFC) and MFC interquartile range (IQR). Obesity did not increase the likelihood of tripping suggesting the increased rate of falls among obese adults is not likely due to a greater likelihood of tripping over an unseen obstacle. Additional results suggested females and individuals of shorter stature have an increased likelihood of tripping compared to their male and taller counterparts. The purpose of the second study was two-fold. First, the effects of load carriage and ramp walking on the likelihood of tripping were investigated, followed by investigating the effects of age and obesity on the likelihood of tripping during load carriage and ramp walking. Again, likelihood of tripping was assessed with median MFC and MFC IQR. Load carriage increased the likelihood of tripping during both level and ramp walking and obesity and age increased the likelihood of tripping during selected combinations of load carriage and/or ramp walking. These results suggest that the increased rate of falls during load carriage and the increased rate of falls among obese and older adult workers reported elsewhere may be due in part to an increased likelihood of tripping. The third study proposed a new method for investigating the likelihood of tripping as a function of obstacle height. The proposed method aimed to clear up ambiguous results often encountered when using MFC central tendency and variability to quantify likelihood of tripping. The method used trip probability curves and a statistical bootstrapping technique to compare trip probability at specific obstacle heights between groups of interest. An additional benefit of this method was that it was able to identify effects of factors not identifiable by the commonly used ANOVA analysis using MFC central tendency and variability. The purpose of the fourth study was to investigate the effects of obesity, age and gender on balance recovery following a lab induced trip perturbation. Measures of balance recovery included fall rate, stepping strategy and characteristics, and trunk kinematics. Obese, older, and female adults fell more frequently after tripping and this higher fall rate may help explain the higher fall rates among obese, older and female adults reported elsewhere. Failed recoveries were associated with higher peak trunk angles and angular velocities in addition to the use of a lowering strategy. Obese, older, and female adults had higher peak trunk angles and angular velocities and older adults and females used lowering strategies more often. These alterations in trunk kinematics and stepping strategy may have contributed to the higher fall rate among these individuals. / Ph. D.

名古屋大学博士学位論文 学位の種類 : 博士(医学)(課程) 学位授与年月日:平成6年3月25日 寳珠山稔氏の博士論文として提出された

Obese and older adults are reported to have a higher rate of mobility limitation and are at a higher risk of fall compared to healthy-weight and young counterparts. To help identify potential mechanisms of these mobility limitations and higher risk of falls, the purpose of the research within this dissertation was to investigate the effects of obesity and age on muscle strength, gait, and balance recovery. Three experimental studies were conducted. The purpose of the first study was to investigate the effects of obesity and age on extension and flexion strength at the hip, knee, and ankle. Absolute strength among obese participants was higher in dorsiflexion, knee extension, and hip flexion compared to healthy-weight participants. Strength relative to body mass was lower among obese participants in all joints/exertions. This lack of uniformity across the 6 exertions is likely due to the still unclear underlying biomechanical mechanism responsible for these strength differences, which may also be influenced by aging. The purpose of the second study was to investigate the effects of obesity, age and, their interactions on relative effort at the hip, knee, and ankle during gait. The peak relative effort for each joint/exertion was expressed by peak NMM during gait as a percentage of the maximum available NMM. The relative effort in hip, knee, and ankle was higher among obese compared to healthy-weight participants. This higher relative effort in hip, knee, and especially in the ankle can be a contributing factor to compromised walking ability among obese individuals. The purpose of the third study was to investigate the effects of age-related strength loss on non-stepping balance recovery capability after a perturbation while standing, without constraining the movements to ankle strategy. The balance recovery capability was quantified by the maximum recoverable platform displacement (MRPD) that was withstood without stepping. Two experiments were conducted. The first experiment involved human subjects and the results suggested that MRPD was lower among older participants compared to young participants. The second experiment involved a simulation study to manipulate muscle strength at hip, knee, and ankle. The results suggested that MRPD was reduced in cases of loss of strength in ankle plantar flexion and hip flexion compared to the young model and did not differ in rest of the cases. The finding suggested that plantar flexor strength plays a major role in capability to recover balance even though the movement was not constrained to the ankle. / Ph. D.

La perte d'équilibre chez l'humain est un phénomène courant de la vie quotidienne. Plusieurs causes peuvent être identifiées, dont notamment des perturbations extérieures. Le scénario qui nous intéresse particulièrement est celui des passagers debout dans les transports en commun. La combinaison de plusieurs études accidentologiques fait ressortir un risque de blessure important pour ce type de situations, surtout pour des passagers debout et/ou âgées. Ces incidents en gendrent des blessures qui coûtent très cher au niveau du budget de la santé. La sécurité de ces passagers est donc à l’origine de ce travail. La perte et/ou le rattrapage d’équilibre est une question complexe qui met en jeu un ensemble de phénomènes tels que la perception de la perturbation, le traitement de l’information, la prise de décision et la mise en œuvre d’actions correctrices. Bien que les connaissances théoriques sur chacun de ces phénomènes soient avancées, il n’existe pas, à l’heure actuelle, de modèle global permettant de représenter la réaction des personnes dans des situations aussi concrètes et complexes que celle des passagers debout de transport en commun.Dans ce contexte, l’objectif principal de ce travail était de développer un outil de simulation pour évaluer les risques associés à la perte d’équilibre des passagers de transport en commun. / Loss of balance is a common phenomenon in our society resulting in injuries and even deaths each year. Among other common sources of destabilization such as slips or trips from an obstacle, the public transportation vehicles are a major source of balance-related injuries to its passengers. Accidental data suggest that the passenger casualties in these vehicles are common, especially to the standing and the elderly passengers, mainly due to the sudden acceleration/deceleration changes of the vehicle. These injuries as well as associated discomfort may discourage people from using these means of transport resulting in adverse economic and societal effects. In this context, the security of the standing passengers in these vehicles constitutes the main motivation of this work.Recovering balance from an external disturbance is a complex process which involves a set of phenomenon such as the perception of the disturbance, information processing, decision making and its implementation. Even though experimental research in the fields of biomechanics and neurosciences provide us with a fair understanding of these phenomena separately, we are unaware of a global model which represents the reaction of people in response to the external disturbances to their equilibrium. In this context, the objective of this work is to develop such a numerical tool which can be used for the assessment of risks associated with the loss of balance of the standing passengers. The essential feature of this tool is the prediction of the post-disturbance kinematics of the subjects depending upon the disturbance characteristics (magnitude, duration etc.) as well as the active recovery response. Another key feature is the representation of the reaction of different populations, especially the elderly, by integrating age effects in the model. For the development of the tool, mathematical modeling (e.g. simplified body representations) and control ideas are borrowed from the field of biped robotics which explicitly deals with the balance issues of bipeds. Further development is done in view of human balance recovery (BR) characteristics. The resulting BR tool shows reasonable predictive capacity of a human balance recovery response confirmed by the comparison of model predictions with experimental balance recovery data.

As quedas são responsáveis pela maior causa de lesões em idosos. Além disso, tratase do incidente mais freqüente que acomete essa população, aumentando de forma exponencial a fragilidade e muitas vezes levando os idosos à morte. Após perturbações inesperadas, a capacidade de readequar o controle postural está notadamente diminuída em idosos, o que leva ao aumento da propensão a quedas nessa população. A reduzida capacidade de reagir a perturbações inesperadas é atribuída a deficiências cumulativas relacionadas ao envelhecimento, tais como a redução da força muscular, diminuição da velocidade de contração muscular e modificações no tempo de reação e capacidade de processamento de informações. Estudos disponibilizam informações sobre uma grande quantidade de procedimentos que foram propostos a fim de minimizar os efeitos do envelhecimento e aumentar a capacidade de controle postural em idosos. Apesar da grande variedade de intervenções disponíveis, poucos estudos reconhecem de fato a razão pela qual a intervenção proposta é, em certos casos, bem ou mal sucedida. Recentemente os mecanismos responsáveis por manter a estabilidade dinâmica do corpo foram determinados em modelos de expressões matemáticas que identificavam as variáveis físicas que atuam no corpo durante a manutenção do equilíbrio postural. A partir de então, certos pesquisadores propõem que o treinamento desses mecanismos por meio da incorporação de movimentos específicos durante uma atividade dinâmica seria fundamental para melhorar as capacidades de controle postural frente a perturbações inesperadas, aumentando a possibilidade de sucesso em intervenções que busquem a prevenção de ocorrência das quedas. Portanto, esse estudo teve como objetivo geral verificar os efeitos de um treinamento realizado no mini trampolim sobre o controle postural de idosos. As hipóteses do presente estudo se baseiam no fato de que um treinamento realizado no mini trampolim, voltado especificamente para o treino dos mecanismos responsáveis pelo controle do equilíbrio postural dinâmico, deverão melhorar a capacidade de reação dos idosos durante um momento de instabilidade postural, prevenindo dessa forma as quedas. Na tentativa de verificar os efeitos do treinamento no mini trampolim sob diferentes enfoques que envolvem situações relacionadas ao controle postural, essa Tese de doutorado foi dividida em três estudos. O primeiro estudo identificou os efeitos do treinamento por 14 semanas no mini trampolim sobre a capacidade de reação e manutenção da estabilidade dos idosos em meio a uma queda súbita para frente. O segundo estudo avaliou a capacidade adaptativa dos idosos no desenvolvimento de reações de equilíbrio eficientes durante uma perturbação súbita e inesperada no teste de marcha, antes e após o período de 14 semanas de treinamento no mini trampolim. O terceiro estudo teve como objetivo avaliar se o treinamento no mini trampolim altera o pico de torque isométrico dos grupos musculares extensor do joelho e flexor plantar do tornozelo e também o desempenho no teste de deslocamento anterior máximo, verificando se existe correlação entre os resultados desses dois testes. Para atingir os objetivos propostos acima, vinte e dois sujeitos com 67±4 anos de idade participaram como voluntários do grupo experimental nesses estudos e doze sujeitos (68±3 anos de idade) participaram do grupo controle, apenas no primeiro estudo. Nos três estudos realizados, os sujeitos foram avaliados em dois momentos: a) previamente a realização do treinamento e b) após as 14 semanas de treinamento no mini trampolim. A avaliação realizada no primeiro e segundo estudos foi baseada na análise da variável conhecida como Margem de Estabilidade. Essa variável permite quantificar precisamente a situação de estabilidade de um corpo em condição dinâmica a partir da análise dos mecanismos responsáveis pela estabilidade, tais como a extrapolação do centro de massa, limites da base de suporte, projeção vertical do centro de massa no solo e velocidade horizontal do centro de massa. Após o treinamento no mini trampolim por 14 semanas (freqüência semanal = duas vezes por semana), os sujeitos treinados foram submetidos a avaliação final. No caso do grupo controle do primeiro experimento, este foi submetido a avaliação final idêntica a primeira após três meses sem qualquer participação em atividades física regulares. Os resultados do primeiro estudo evidenciam que os idosos possuem melhor performance no teste de queda para frente após serem submetidos ao treinamento no mini trampolim. A variável margem de estabilidade revelou que os sujeitos conseguiram restabelecer o controle do equilíbrio dinâmico durante a queda para frente a partir de maiores inclinações corporais (posturas mais instáveis) quando comparados a avaliação inicial e ao desempenho do grupo controle. Os resultados indicam também o aumento da velocidade de aumento da base de suporte, sugerindo que esse foi o mecanismo responsável pela melhora do desempenho no teste de queda para frente após o período de treinamento. No segundo estudo os resultados mostram que os idosos, após freqüentarem o treinamento, possuem maior capacidade de reação e adaptação a perturbações inesperadas. Os dados indicaram, por meio da melhora da variável margem de estabilidade, que a magnitude da capacidade de adaptação foi maior e que as reações mediadas por feedback proprioceptivo tornaram-se mais eficazes em conter a instabilidade postural. O estudo aponta que a capacidade de aumento da base de suporte durante a reação a uma perturbação inesperada foi o mecanismo preponderante responsável pela melhora no desempenho no teste após o treino por 14 semanas no mini trampolim. O terceiro estudo revelou que o treino no mini trampolim produziu aumento da capacidade de produção de torque flexor plantar do tornozelo durante uma contração isométrica voluntária máxima; no entanto, o mesmo não ocorreu para o grupo muscular extensor do joelho. Esse estudo evidenciou ainda a melhora na capacidade de deslocamento anterior do corpo por meio da análise do comportamento do centro de pressão em relação à base de suporte do sujeito. A partir da correlação existente entre os resultados de pico de torque e deslocamento anterior máximo, foi possível sugerir que o aumento do torque muscular flexor plantar de tornozelo gerado pelo treinamento foi o responsável pela melhora no desempenho do teste de deslocamento anterior, e que a força muscular é condição importante para o controle postural neste teste estático. Em resumo, os resultados dos estudos realizados nessa Tese evidenciaram, sob diferentes enfoques biomecânicos, que a intervenção realizada com idosos no mini trampolim por 14 semanas, baseada em exercícios que buscavam treinar os mecanismos responsáveis pela estabilidade dinâmica, são capazes de melhorar (1) as reações posturais durante o restabelecimento do equilíbrio dinâmico no teste de queda para frente, (2) as respostas posturais preditivas e reativas em meio a uma perturbação inesperada durante a marcha, (3) o desempenho no teste de controle postural estático de deslocamento anterior máximo e (4) e aumentar o pico de torque isométrico dos músculos flexores plantares do tornozelo. Assim pode-se concluir que o treinamento no mini trampolim e, principalmente, o treinamento dos mecanismos responsáveis pelo controle da estabilidade dinâmica, são ferramentas eficazes a serem utilizadas em atividades que pretendam reduzir o risco de quedas e aumentar a estabilidade postural de idosos. / Falls are the major cause of injuries in the elderly. Moreover, it is the most frequent cause of injury amongst the elderly, increasing their vulnerability and, not rarely, leading to death. After a sudden perturbation, the capacity of regaining postural control is clearly diminished in the elderly. The reduced capacity to react during unexpected perturbations come as a result of the age-related cumulative deficiencies, such as lower muscle strength, contraction velocity, reaction time and the reduced capacity of information processing. Several studies aiming at minimizing the age-related deficiencies and enhancing postural control capacities can be found in the literature. However, only a few have searched for the reasons that had led to the intervention outcomes. Recently, the mechanisms through which the dynamic stability is maintained have been described, identifying some important variables acting during the dynamic stability recovery. Concerning these findings some researchers suggest that training interventions with a high dynamic component, incorporating specific movements that exercise the mechanisms responsible for the dynamic stability could enhance postural control during unexpected perturbations and would improve the possibility of success of interventions that intend to prevent falls in the elderly. Therefore, the purpose of this study was to analyze the effects of a mini trampoline training on elderly postural control. We hypothesize that a mini trampoline training based on exercises that enhance the mechanisms through which the dynamic stability is maintained would be an efficient intervention to improve the postural stability reactions during unexpected perturbations and prevent falls. In an attempt at studying the effects of the trampoline training through different approaches and circumstances of the postural control, this thesis was divided into three studies. The first study aimed at investigating the effects of a 14-week mini trampoline training on the postural recovery capacities during a sudden forward fall. The second, assessed the capacities of developing efficient adaptative adjustments to recover from unexpected perturbations during locomotion after the 14-week mini trampoline training for the elderly. The third, evaluated the effects of mini trampoline training on: a) the peak isometric torque of knee extensors and ankle plantarflexors muscles; b) the center of pressure (CP) displacement during maximal anterior body inclination and c) if there was a correlation between the results of muscle force and the maximal anterior body displacement task. In order to achieve the objectives described above, twenty two elderly subjects (67±4 years) were taken as volunteers for the experimental group (trained group) and additionally twelve subjects (68±3 years) were included as controls for the first study. During the procedure of the three studies the trained subjects were assessed in two moments: a) previously to the mini trampoline training (pre measurement) and b) after the 14-week mini trampoline training period (post measurement) or after 3 months for the control group (post measurement). The assessments of the first and second studies were based on the variable called “margin of stability”. This method was described by Hof et al. (2005), and allows a precise measurement of the dynamic stability situation of a body by the analysis of the mechanisms responsible for maintaining the dynamic stability, such as extrapolation of Center of Mass (CM), boundaries of base of support (BoS), vertical projection of the CM to the ground, horizontal velocity of CM among others. The results of the first study showed that the trained elderly improved their recovery performance after a sudden forward fall after the mini trampoline training. The variable margin of stability at the instant of release of the forward fall decreased after training, showing that the subjects were able to recover stability with a single step from more inclined positions (more unstable positions) while compared either to pre-measurement and to the control group performance. The results also showed that the higher rate of BoS increase was the main parameter responsible for the improvement in the dynamic stability control after training. The results of the second study showed evidence that after the training period the trained subjects increased their postural reaction and adaptation capacities during sudden perturbations in the gait. The data indicated that the higher capacity of increase the BoS after the mini trampoline training was the main factor responsible for the more efficient feedback reactions as well as predictive responses while recovering from a perturbation in the gait protocol. The third study revealed that the training increased the peak torque of the ankle plantarflexors, but not from the knee extensors during a maximal isometric voluntary contraction. In addition, the results showed an improvement in the maximal CP displacement related to the BoS, leading to shorter distances between BoS and CP. The negative correlation between the results from peak ankle plantarflexors torque and the distances (BoS – CP) suggests that the higher torque produced after the training is important for stability and was the responsible for the improvement on the static balance task related to the maximal anterior projection of the body. In summary, the results of the three studies performed in the thesis under different approaches showed evidences that the 14-week mini trampoline training intervention based on exercises that enhance the mechanisms responsible for dynamic stability were capable to improve (1) elderly dynamic stability postural reactions while recovering from a forward fall with a single step, (2) the predictive and the reactive feedback mediated responses in the recovery of an unexpected perturbation during locomotion, (3) the peak isometric torque of the ankle plantarflexors and (4) the performance in the static balance task of maximal anterior body projection. Therefore, it is possible to conclude that the mini trampoline training, and specially the training of the mechanisms responsible for dynamic stability, is an efficient approach that should be used and stimulated in every intervention that wishes to reduce the fall risk and improve the postural stability in the elderly.

As quedas são responsáveis pela maior causa de lesões em idosos. Além disso, tratase do incidente mais freqüente que acomete essa população, aumentando de forma exponencial a fragilidade e muitas vezes levando os idosos à morte. Após perturbações inesperadas, a capacidade de readequar o controle postural está notadamente diminuída em idosos, o que leva ao aumento da propensão a quedas nessa população. A reduzida capacidade de reagir a perturbações inesperadas é atribuída a deficiências cumulativas relacionadas ao envelhecimento, tais como a redução da força muscular, diminuição da velocidade de contração muscular e modificações no tempo de reação e capacidade de processamento de informações. Estudos disponibilizam informações sobre uma grande quantidade de procedimentos que foram propostos a fim de minimizar os efeitos do envelhecimento e aumentar a capacidade de controle postural em idosos. Apesar da grande variedade de intervenções disponíveis, poucos estudos reconhecem de fato a razão pela qual a intervenção proposta é, em certos casos, bem ou mal sucedida. Recentemente os mecanismos responsáveis por manter a estabilidade dinâmica do corpo foram determinados em modelos de expressões matemáticas que identificavam as variáveis físicas que atuam no corpo durante a manutenção do equilíbrio postural. A partir de então, certos pesquisadores propõem que o treinamento desses mecanismos por meio da incorporação de movimentos específicos durante uma atividade dinâmica seria fundamental para melhorar as capacidades de controle postural frente a perturbações inesperadas, aumentando a possibilidade de sucesso em intervenções que busquem a prevenção de ocorrência das quedas. Portanto, esse estudo teve como objetivo geral verificar os efeitos de um treinamento realizado no mini trampolim sobre o controle postural de idosos. As hipóteses do presente estudo se baseiam no fato de que um treinamento realizado no mini trampolim, voltado especificamente para o treino dos mecanismos responsáveis pelo controle do equilíbrio postural dinâmico, deverão melhorar a capacidade de reação dos idosos durante um momento de instabilidade postural, prevenindo dessa forma as quedas. Na tentativa de verificar os efeitos do treinamento no mini trampolim sob diferentes enfoques que envolvem situações relacionadas ao controle postural, essa Tese de doutorado foi dividida em três estudos. O primeiro estudo identificou os efeitos do treinamento por 14 semanas no mini trampolim sobre a capacidade de reação e manutenção da estabilidade dos idosos em meio a uma queda súbita para frente. O segundo estudo avaliou a capacidade adaptativa dos idosos no desenvolvimento de reações de equilíbrio eficientes durante uma perturbação súbita e inesperada no teste de marcha, antes e após o período de 14 semanas de treinamento no mini trampolim. O terceiro estudo teve como objetivo avaliar se o treinamento no mini trampolim altera o pico de torque isométrico dos grupos musculares extensor do joelho e flexor plantar do tornozelo e também o desempenho no teste de deslocamento anterior máximo, verificando se existe correlação entre os resultados desses dois testes. Para atingir os objetivos propostos acima, vinte e dois sujeitos com 67±4 anos de idade participaram como voluntários do grupo experimental nesses estudos e doze sujeitos (68±3 anos de idade) participaram do grupo controle, apenas no primeiro estudo. Nos três estudos realizados, os sujeitos foram avaliados em dois momentos: a) previamente a realização do treinamento e b) após as 14 semanas de treinamento no mini trampolim. A avaliação realizada no primeiro e segundo estudos foi baseada na análise da variável conhecida como Margem de Estabilidade. Essa variável permite quantificar precisamente a situação de estabilidade de um corpo em condição dinâmica a partir da análise dos mecanismos responsáveis pela estabilidade, tais como a extrapolação do centro de massa, limites da base de suporte, projeção vertical do centro de massa no solo e velocidade horizontal do centro de massa. Após o treinamento no mini trampolim por 14 semanas (freqüência semanal = duas vezes por semana), os sujeitos treinados foram submetidos a avaliação final. No caso do grupo controle do primeiro experimento, este foi submetido a avaliação final idêntica a primeira após três meses sem qualquer participação em atividades física regulares. Os resultados do primeiro estudo evidenciam que os idosos possuem melhor performance no teste de queda para frente após serem submetidos ao treinamento no mini trampolim. A variável margem de estabilidade revelou que os sujeitos conseguiram restabelecer o controle do equilíbrio dinâmico durante a queda para frente a partir de maiores inclinações corporais (posturas mais instáveis) quando comparados a avaliação inicial e ao desempenho do grupo controle. Os resultados indicam também o aumento da velocidade de aumento da base de suporte, sugerindo que esse foi o mecanismo responsável pela melhora do desempenho no teste de queda para frente após o período de treinamento. No segundo estudo os resultados mostram que os idosos, após freqüentarem o treinamento, possuem maior capacidade de reação e adaptação a perturbações inesperadas. Os dados indicaram, por meio da melhora da variável margem de estabilidade, que a magnitude da capacidade de adaptação foi maior e que as reações mediadas por feedback proprioceptivo tornaram-se mais eficazes em conter a instabilidade postural. O estudo aponta que a capacidade de aumento da base de suporte durante a reação a uma perturbação inesperada foi o mecanismo preponderante responsável pela melhora no desempenho no teste após o treino por 14 semanas no mini trampolim. O terceiro estudo revelou que o treino no mini trampolim produziu aumento da capacidade de produção de torque flexor plantar do tornozelo durante uma contração isométrica voluntária máxima; no entanto, o mesmo não ocorreu para o grupo muscular extensor do joelho. Esse estudo evidenciou ainda a melhora na capacidade de deslocamento anterior do corpo por meio da análise do comportamento do centro de pressão em relação à base de suporte do sujeito. A partir da correlação existente entre os resultados de pico de torque e deslocamento anterior máximo, foi possível sugerir que o aumento do torque muscular flexor plantar de tornozelo gerado pelo treinamento foi o responsável pela melhora no desempenho do teste de deslocamento anterior, e que a força muscular é condição importante para o controle postural neste teste estático. Em resumo, os resultados dos estudos realizados nessa Tese evidenciaram, sob diferentes enfoques biomecânicos, que a intervenção realizada com idosos no mini trampolim por 14 semanas, baseada em exercícios que buscavam treinar os mecanismos responsáveis pela estabilidade dinâmica, são capazes de melhorar (1) as reações posturais durante o restabelecimento do equilíbrio dinâmico no teste de queda para frente, (2) as respostas posturais preditivas e reativas em meio a uma perturbação inesperada durante a marcha, (3) o desempenho no teste de controle postural estático de deslocamento anterior máximo e (4) e aumentar o pico de torque isométrico dos músculos flexores plantares do tornozelo. Assim pode-se concluir que o treinamento no mini trampolim e, principalmente, o treinamento dos mecanismos responsáveis pelo controle da estabilidade dinâmica, são ferramentas eficazes a serem utilizadas em atividades que pretendam reduzir o risco de quedas e aumentar a estabilidade postural de idosos. / Falls are the major cause of injuries in the elderly. Moreover, it is the most frequent cause of injury amongst the elderly, increasing their vulnerability and, not rarely, leading to death. After a sudden perturbation, the capacity of regaining postural control is clearly diminished in the elderly. The reduced capacity to react during unexpected perturbations come as a result of the age-related cumulative deficiencies, such as lower muscle strength, contraction velocity, reaction time and the reduced capacity of information processing. Several studies aiming at minimizing the age-related deficiencies and enhancing postural control capacities can be found in the literature. However, only a few have searched for the reasons that had led to the intervention outcomes. Recently, the mechanisms through which the dynamic stability is maintained have been described, identifying some important variables acting during the dynamic stability recovery. Concerning these findings some researchers suggest that training interventions with a high dynamic component, incorporating specific movements that exercise the mechanisms responsible for the dynamic stability could enhance postural control during unexpected perturbations and would improve the possibility of success of interventions that intend to prevent falls in the elderly. Therefore, the purpose of this study was to analyze the effects of a mini trampoline training on elderly postural control. We hypothesize that a mini trampoline training based on exercises that enhance the mechanisms through which the dynamic stability is maintained would be an efficient intervention to improve the postural stability reactions during unexpected perturbations and prevent falls. In an attempt at studying the effects of the trampoline training through different approaches and circumstances of the postural control, this thesis was divided into three studies. The first study aimed at investigating the effects of a 14-week mini trampoline training on the postural recovery capacities during a sudden forward fall. The second, assessed the capacities of developing efficient adaptative adjustments to recover from unexpected perturbations during locomotion after the 14-week mini trampoline training for the elderly. The third, evaluated the effects of mini trampoline training on: a) the peak isometric torque of knee extensors and ankle plantarflexors muscles; b) the center of pressure (CP) displacement during maximal anterior body inclination and c) if there was a correlation between the results of muscle force and the maximal anterior body displacement task. In order to achieve the objectives described above, twenty two elderly subjects (67±4 years) were taken as volunteers for the experimental group (trained group) and additionally twelve subjects (68±3 years) were included as controls for the first study. During the procedure of the three studies the trained subjects were assessed in two moments: a) previously to the mini trampoline training (pre measurement) and b) after the 14-week mini trampoline training period (post measurement) or after 3 months for the control group (post measurement). The assessments of the first and second studies were based on the variable called “margin of stability”. This method was described by Hof et al. (2005), and allows a precise measurement of the dynamic stability situation of a body by the analysis of the mechanisms responsible for maintaining the dynamic stability, such as extrapolation of Center of Mass (CM), boundaries of base of support (BoS), vertical projection of the CM to the ground, horizontal velocity of CM among others. The results of the first study showed that the trained elderly improved their recovery performance after a sudden forward fall after the mini trampoline training. The variable margin of stability at the instant of release of the forward fall decreased after training, showing that the subjects were able to recover stability with a single step from more inclined positions (more unstable positions) while compared either to pre-measurement and to the control group performance. The results also showed that the higher rate of BoS increase was the main parameter responsible for the improvement in the dynamic stability control after training. The results of the second study showed evidence that after the training period the trained subjects increased their postural reaction and adaptation capacities during sudden perturbations in the gait. The data indicated that the higher capacity of increase the BoS after the mini trampoline training was the main factor responsible for the more efficient feedback reactions as well as predictive responses while recovering from a perturbation in the gait protocol. The third study revealed that the training increased the peak torque of the ankle plantarflexors, but not from the knee extensors during a maximal isometric voluntary contraction. In addition, the results showed an improvement in the maximal CP displacement related to the BoS, leading to shorter distances between BoS and CP. The negative correlation between the results from peak ankle plantarflexors torque and the distances (BoS – CP) suggests that the higher torque produced after the training is important for stability and was the responsible for the improvement on the static balance task related to the maximal anterior projection of the body. In summary, the results of the three studies performed in the thesis under different approaches showed evidences that the 14-week mini trampoline training intervention based on exercises that enhance the mechanisms responsible for dynamic stability were capable to improve (1) elderly dynamic stability postural reactions while recovering from a forward fall with a single step, (2) the predictive and the reactive feedback mediated responses in the recovery of an unexpected perturbation during locomotion, (3) the peak isometric torque of the ankle plantarflexors and (4) the performance in the static balance task of maximal anterior body projection. Therefore, it is possible to conclude that the mini trampoline training, and specially the training of the mechanisms responsible for dynamic stability, is an efficient approach that should be used and stimulated in every intervention that wishes to reduce the fall risk and improve the postural stability in the elderly.

As quedas são responsáveis pela maior causa de lesões em idosos. Além disso, tratase do incidente mais freqüente que acomete essa população, aumentando de forma exponencial a fragilidade e muitas vezes levando os idosos à morte. Após perturbações inesperadas, a capacidade de readequar o controle postural está notadamente diminuída em idosos, o que leva ao aumento da propensão a quedas nessa população. A reduzida capacidade de reagir a perturbações inesperadas é atribuída a deficiências cumulativas relacionadas ao envelhecimento, tais como a redução da força muscular, diminuição da velocidade de contração muscular e modificações no tempo de reação e capacidade de processamento de informações. Estudos disponibilizam informações sobre uma grande quantidade de procedimentos que foram propostos a fim de minimizar os efeitos do envelhecimento e aumentar a capacidade de controle postural em idosos. Apesar da grande variedade de intervenções disponíveis, poucos estudos reconhecem de fato a razão pela qual a intervenção proposta é, em certos casos, bem ou mal sucedida. Recentemente os mecanismos responsáveis por manter a estabilidade dinâmica do corpo foram determinados em modelos de expressões matemáticas que identificavam as variáveis físicas que atuam no corpo durante a manutenção do equilíbrio postural. A partir de então, certos pesquisadores propõem que o treinamento desses mecanismos por meio da incorporação de movimentos específicos durante uma atividade dinâmica seria fundamental para melhorar as capacidades de controle postural frente a perturbações inesperadas, aumentando a possibilidade de sucesso em intervenções que busquem a prevenção de ocorrência das quedas. Portanto, esse estudo teve como objetivo geral verificar os efeitos de um treinamento realizado no mini trampolim sobre o controle postural de idosos. As hipóteses do presente estudo se baseiam no fato de que um treinamento realizado no mini trampolim, voltado especificamente para o treino dos mecanismos responsáveis pelo controle do equilíbrio postural dinâmico, deverão melhorar a capacidade de reação dos idosos durante um momento de instabilidade postural, prevenindo dessa forma as quedas. Na tentativa de verificar os efeitos do treinamento no mini trampolim sob diferentes enfoques que envolvem situações relacionadas ao controle postural, essa Tese de doutorado foi dividida em três estudos. O primeiro estudo identificou os efeitos do treinamento por 14 semanas no mini trampolim sobre a capacidade de reação e manutenção da estabilidade dos idosos em meio a uma queda súbita para frente. O segundo estudo avaliou a capacidade adaptativa dos idosos no desenvolvimento de reações de equilíbrio eficientes durante uma perturbação súbita e inesperada no teste de marcha, antes e após o período de 14 semanas de treinamento no mini trampolim. O terceiro estudo teve como objetivo avaliar se o treinamento no mini trampolim altera o pico de torque isométrico dos grupos musculares extensor do joelho e flexor plantar do tornozelo e também o desempenho no teste de deslocamento anterior máximo, verificando se existe correlação entre os resultados desses dois testes. Para atingir os objetivos propostos acima, vinte e dois sujeitos com 67±4 anos de idade participaram como voluntários do grupo experimental nesses estudos e doze sujeitos (68±3 anos de idade) participaram do grupo controle, apenas no primeiro estudo. Nos três estudos realizados, os sujeitos foram avaliados em dois momentos: a) previamente a realização do treinamento e b) após as 14 semanas de treinamento no mini trampolim. A avaliação realizada no primeiro e segundo estudos foi baseada na análise da variável conhecida como Margem de Estabilidade. Essa variável permite quantificar precisamente a situação de estabilidade de um corpo em condição dinâmica a partir da análise dos mecanismos responsáveis pela estabilidade, tais como a extrapolação do centro de massa, limites da base de suporte, projeção vertical do centro de massa no solo e velocidade horizontal do centro de massa. Após o treinamento no mini trampolim por 14 semanas (freqüência semanal = duas vezes por semana), os sujeitos treinados foram submetidos a avaliação final. No caso do grupo controle do primeiro experimento, este foi submetido a avaliação final idêntica a primeira após três meses sem qualquer participação em atividades física regulares. Os resultados do primeiro estudo evidenciam que os idosos possuem melhor performance no teste de queda para frente após serem submetidos ao treinamento no mini trampolim. A variável margem de estabilidade revelou que os sujeitos conseguiram restabelecer o controle do equilíbrio dinâmico durante a queda para frente a partir de maiores inclinações corporais (posturas mais instáveis) quando comparados a avaliação inicial e ao desempenho do grupo controle. Os resultados indicam também o aumento da velocidade de aumento da base de suporte, sugerindo que esse foi o mecanismo responsável pela melhora do desempenho no teste de queda para frente após o período de treinamento. No segundo estudo os resultados mostram que os idosos, após freqüentarem o treinamento, possuem maior capacidade de reação e adaptação a perturbações inesperadas. Os dados indicaram, por meio da melhora da variável margem de estabilidade, que a magnitude da capacidade de adaptação foi maior e que as reações mediadas por feedback proprioceptivo tornaram-se mais eficazes em conter a instabilidade postural. O estudo aponta que a capacidade de aumento da base de suporte durante a reação a uma perturbação inesperada foi o mecanismo preponderante responsável pela melhora no desempenho no teste após o treino por 14 semanas no mini trampolim. O terceiro estudo revelou que o treino no mini trampolim produziu aumento da capacidade de produção de torque flexor plantar do tornozelo durante uma contração isométrica voluntária máxima; no entanto, o mesmo não ocorreu para o grupo muscular extensor do joelho. Esse estudo evidenciou ainda a melhora na capacidade de deslocamento anterior do corpo por meio da análise do comportamento do centro de pressão em relação à base de suporte do sujeito. A partir da correlação existente entre os resultados de pico de torque e deslocamento anterior máximo, foi possível sugerir que o aumento do torque muscular flexor plantar de tornozelo gerado pelo treinamento foi o responsável pela melhora no desempenho do teste de deslocamento anterior, e que a força muscular é condição importante para o controle postural neste teste estático. Em resumo, os resultados dos estudos realizados nessa Tese evidenciaram, sob diferentes enfoques biomecânicos, que a intervenção realizada com idosos no mini trampolim por 14 semanas, baseada em exercícios que buscavam treinar os mecanismos responsáveis pela estabilidade dinâmica, são capazes de melhorar (1) as reações posturais durante o restabelecimento do equilíbrio dinâmico no teste de queda para frente, (2) as respostas posturais preditivas e reativas em meio a uma perturbação inesperada durante a marcha, (3) o desempenho no teste de controle postural estático de deslocamento anterior máximo e (4) e aumentar o pico de torque isométrico dos músculos flexores plantares do tornozelo. Assim pode-se concluir que o treinamento no mini trampolim e, principalmente, o treinamento dos mecanismos responsáveis pelo controle da estabilidade dinâmica, são ferramentas eficazes a serem utilizadas em atividades que pretendam reduzir o risco de quedas e aumentar a estabilidade postural de idosos. / Falls are the major cause of injuries in the elderly. Moreover, it is the most frequent cause of injury amongst the elderly, increasing their vulnerability and, not rarely, leading to death. After a sudden perturbation, the capacity of regaining postural control is clearly diminished in the elderly. The reduced capacity to react during unexpected perturbations come as a result of the age-related cumulative deficiencies, such as lower muscle strength, contraction velocity, reaction time and the reduced capacity of information processing. Several studies aiming at minimizing the age-related deficiencies and enhancing postural control capacities can be found in the literature. However, only a few have searched for the reasons that had led to the intervention outcomes. Recently, the mechanisms through which the dynamic stability is maintained have been described, identifying some important variables acting during the dynamic stability recovery. Concerning these findings some researchers suggest that training interventions with a high dynamic component, incorporating specific movements that exercise the mechanisms responsible for the dynamic stability could enhance postural control during unexpected perturbations and would improve the possibility of success of interventions that intend to prevent falls in the elderly. Therefore, the purpose of this study was to analyze the effects of a mini trampoline training on elderly postural control. We hypothesize that a mini trampoline training based on exercises that enhance the mechanisms through which the dynamic stability is maintained would be an efficient intervention to improve the postural stability reactions during unexpected perturbations and prevent falls. In an attempt at studying the effects of the trampoline training through different approaches and circumstances of the postural control, this thesis was divided into three studies. The first study aimed at investigating the effects of a 14-week mini trampoline training on the postural recovery capacities during a sudden forward fall. The second, assessed the capacities of developing efficient adaptative adjustments to recover from unexpected perturbations during locomotion after the 14-week mini trampoline training for the elderly. The third, evaluated the effects of mini trampoline training on: a) the peak isometric torque of knee extensors and ankle plantarflexors muscles; b) the center of pressure (CP) displacement during maximal anterior body inclination and c) if there was a correlation between the results of muscle force and the maximal anterior body displacement task. In order to achieve the objectives described above, twenty two elderly subjects (67±4 years) were taken as volunteers for the experimental group (trained group) and additionally twelve subjects (68±3 years) were included as controls for the first study. During the procedure of the three studies the trained subjects were assessed in two moments: a) previously to the mini trampoline training (pre measurement) and b) after the 14-week mini trampoline training period (post measurement) or after 3 months for the control group (post measurement). The assessments of the first and second studies were based on the variable called “margin of stability”. This method was described by Hof et al. (2005), and allows a precise measurement of the dynamic stability situation of a body by the analysis of the mechanisms responsible for maintaining the dynamic stability, such as extrapolation of Center of Mass (CM), boundaries of base of support (BoS), vertical projection of the CM to the ground, horizontal velocity of CM among others. The results of the first study showed that the trained elderly improved their recovery performance after a sudden forward fall after the mini trampoline training. The variable margin of stability at the instant of release of the forward fall decreased after training, showing that the subjects were able to recover stability with a single step from more inclined positions (more unstable positions) while compared either to pre-measurement and to the control group performance. The results also showed that the higher rate of BoS increase was the main parameter responsible for the improvement in the dynamic stability control after training. The results of the second study showed evidence that after the training period the trained subjects increased their postural reaction and adaptation capacities during sudden perturbations in the gait. The data indicated that the higher capacity of increase the BoS after the mini trampoline training was the main factor responsible for the more efficient feedback reactions as well as predictive responses while recovering from a perturbation in the gait protocol. The third study revealed that the training increased the peak torque of the ankle plantarflexors, but not from the knee extensors during a maximal isometric voluntary contraction. In addition, the results showed an improvement in the maximal CP displacement related to the BoS, leading to shorter distances between BoS and CP. The negative correlation between the results from peak ankle plantarflexors torque and the distances (BoS – CP) suggests that the higher torque produced after the training is important for stability and was the responsible for the improvement on the static balance task related to the maximal anterior projection of the body. In summary, the results of the three studies performed in the thesis under different approaches showed evidences that the 14-week mini trampoline training intervention based on exercises that enhance the mechanisms responsible for dynamic stability were capable to improve (1) elderly dynamic stability postural reactions while recovering from a forward fall with a single step, (2) the predictive and the reactive feedback mediated responses in the recovery of an unexpected perturbation during locomotion, (3) the peak isometric torque of the ankle plantarflexors and (4) the performance in the static balance task of maximal anterior body projection. Therefore, it is possible to conclude that the mini trampoline training, and specially the training of the mechanisms responsible for dynamic stability, is an efficient approach that should be used and stimulated in every intervention that wishes to reduce the fall risk and improve the postural stability in the elderly.