Este estudo investigou como padrões de coordenação postural durante movimentos voluntários do corpo todo durante a postura ereta são afetados pelo envelhencimento usando o paradigma da relação entre velocidade e acurácia. Dez idosos e dez adultos jovens permaneceram em pé sobre uma plataforma de força e tiveram a posição instantânea do centro de pressão (CP) mostrada como feedback visual em um monitor a um metro a frente. Os participantes executaram movimentos contínuos rápidos e acurados na direção ântero-posterior com o corpo todo movendo a posição do CP entre alvos de diferentes larguras ou em diferentes freqüências de movimento, durante 45 s. Tempo de movimento (TM), deslocamento do CP, excursão dos ângulos articulares e atividade eletromiográfica (EMG) dos músculos do tornozelo, joelho e quadril foram analisados. Análises de componentes principais (PC) dos ângulos articulares foram também efetuadas. Flexibilidade da coordenação postural foi avaliada usando a abordagem da variedade não controlada (UCM) para testar as hipóteses de estabilização do tronco e do centro de massa (CM). Ambos grupos aumentaram o TM, atividade EMG e variáveis cinemáticas com um aumento na acurácia e freqüência. Sujeitos idosos aumentaram a amplitude dos ângulos articulares e EMG comparados aos adultos. Análise de PC mostrou alto acoplamento entre as articulações e a análise do UCM confirmou as hipóteses de estabilização do tronco e do CM. Os resultados indicam que padrões de coordenação postural são afetados pela acurácia dos movimentos do corpo todo e algumas dessas alterações estão relacionadas ao envelhecimento / This study examined how postural coodination patterns during voluntary whole-body movements in standing are affected by aging using the speed-accuracy trade-off paradigm. Ten elderly subjects and ten young adults stood on a force plate and had their center of pressure (COP) instantaneous position shown as visual feedback on a computer monitor one meter ahead. The participants performed continuous fast and accurate movements in the anterior-posterior direction with the whole body shifting their COP position; between targets with different widths or in different movement frequencies, during 45 s. Movement time (MT), COP displacement, joint angle excursion and eletromyographic (EMG) activity of ankle, knee and hip muscles were analyzed. Principal component (PC) analyses of the joint angles were also carried out. Flexibility of the postural coordination was evaluated using uncontrolled manifold (UCM) approach to test the trunk and the center of mass (COM) stabilization hypothesis. Both groups increased the MT, EMG activity and kinematic variables with an increase in the accuracy and frequency. Elderly subjects increased joint angles and EMG amplitude compared to adults. PC analysis showed a high coupling among the joints and the UCM analysis confirmed the trunk and the COM stabilization hypothesis. The results indicated that postural coordination patterns are affected by accuracy of whole-body movements and some changes are correlated with to aging

Des données récentes suggèrent que l'exécution d'une tâche induisant des saccades améliore la stabilité par rapport à la fixation statique. Cependant, elles supposent la linéarité du contrôle postural en interprétant uniquement la zone de déplacement et/ou la vitesse de balancement. A l'inverse, des mesures non linéaires pourraient apporter une meilleure compréhension du contrôle postural. L'objectif est d'examiner l'effet des mouvements oculaires sur différentes mesures linéaires et non linéaires de la stabilité. On a demandé à 21 adultes en bonne santé (24,0±3,3 ans) de se tenir debout sur une plate-forme de force, pieds joints, et de regarder le moniteur situé devant eux. Cinq conditions ont été testées : yeux fermés, regard aléatoire, point statique fixe, saccade et poursuite visuelle. Cinq essais de 60 secondes par condition ont été réalisés. Une ANOVA à mesures répétées a été réalisée pour chaque variable de contrôle postural dans chaque direction : antéro-postérieure (AP) et médio-latérale (ML). L'absence de vision a eu un impact négatif sur le contrôle de la posture, comme en témoigne une augmentation de l'aire et de la variabilité du balancement ainsi qu'une réduction des contributions de la bande « ultra-low ». La saccade a conduit à une plus grande stabilité que le regard aléatoire, comme en témoigne une zone plus petite. Cependant, la poursuite visuelle a entraîné une diminution de la stabilité par rapport au regard aléatoire, comme le montre une zone d’oscillation plus grande, ainsi qu'une augmentation de la variabilité. Il convient de noter que l'énergie contenue dans la bande « very-low », qui indique la contribution du système vestibulaire, était plus élevée dans la poursuite visuelle que dans le point statique fixe.

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An increase in postural sway is one of the risk factors that have been linked to an increased incidence of falls in the older adult population. Researchers have shown that peripheral sensation is crucial in maintaining a static posture for adults of all ages. It has been reported that older adults have decreased tactile sensation of the plantar surface of their feet. and when the sensory feedback was increased older adults had improved postural control. It was hypothesized that facilitation of the sole of the foot with the use of a semirigid foot orthotic would result in improved postural stability in older adults. Twenty-seven volunteers (19 females, 8 males, mean age: 87 ± 5 yrs) were recruited as subjects from a retirement community. All subjects were supplied with the SmartStep™ Stabilization System. There were a total of 5 Test Days for each subject. The first 2 Test Days were performed while the subjects wore their own shoes, while the last 3 Test Days were performed while the subjects wore the SmartStep™. Test Days 1 and 2 were performed 48 hours apart. Test Day 3 occurred 2 to 4 weeks after Test 2. Test Days 4 and 5 occurred 4-weeks after the prior Test Day. During the 8-weeks between Test Days 3 and 5, subjects were asked to wear the SmartStep™ as their daily shoe. Clinical measures of balance, force plate measurements, sensation testing, and confidence and activity scales were collected on all subjects throughout the eight week test period. Statistical significance was found for 3 of the clinical measures. The Timed “Up & Go” improved from 17.25 to 15.47 sec. The Functional Reach and Lateral Reach Tests demonstrated a decline in scores during the eight weeks. There was only 1 statistically significant finding for the force plate measures. The center of pressure displacement in the anteriorposterior direction was increased from 4.6 to 5.3 cm. No significant differences where reported for any other dependent variable. The results did not indicate statistically that the in-shoe orthotic enhanced postural stability in this group of subjects. However, there were indications that there was a subset of the current population that benefited from the intervention and this needs to be investigated further.

INTRODUÇÃO: Atletas de futebol podem ter melhor equilíbrio que sedentários, pois os programas de treinamento sensório-motor melhoram a função motora, aumentam o controle neuromuscular e promovem a melhora da propriocepção. Este estudo teve como objetivos: avaliar o equilíbrio postural e a influência da dominância e dos fatores antropométricos em atletas de futebol de campo e indivíduos sedentários. MÉTODOS: Foram avaliados 100 indivíduos do gênero masculino divididos em dois grupos: 50 atletas de futebol de campo (GA) com idade de 18,0+0,7 anos e 50 indivíduos sedentários (GS) com idade de 17,6+0,6 anos. Os grupos foram analisados em relação à massa corporal, estatura, índice de massa corporal (IMC), flexibilidade e percentagem de gordura. Para avaliação do equilíbrio foi utilizado o protocolo Dynamic Balance System, nível 8 de estabilidade do equipamento Biodex Balance System (BBS). RESULTADOS: Os atletas apresentaram melhores índices no membro dominante no teste para a direita (p = 0,039) e no membro não-dominante no teste para trás/esquerda (p=0,007). Os sedentários tiveram melhores índices no teste realizado para a direita (p=0,034) no membro não dominante. Nos demais índices, não houve diferença estatística. O GS teve melhor desempenho do membro não dominante quando comparado com o dominante na maioria dos testes realizados. No GA houve melhor desempenho do membro não dominante no índice de estabilidade geral (p=0,027) e para esquerda (p=0,009). Houve fraca correlação entre medidas antropométricas e os índices de equilíbrio medidos pelo BBS nos dois grupos. CONCLUSÕES: Não há diferença no equilíbrio postural de atletas de futebol de campo e indivíduos sedentários. A dominância afeta o equilíbrio unipodal dos indivíduos sedentários, mas não afeta dos atletas de futebol de campo da categoria juniores. Os fatores antropométricos não interferiram no equilíbrio / INTRODUCTION: Soccer athletes may have a better balance than sedentary individuals, once sensory-motor training programs improve the motor function, increase neuromuscular control and promote a better balance and proprioception. The aim of this study was to assess the postural balance and the influence of the dominance and of anthropometric measures on field soccer athletes and sedentary individuals. METHODS: One hundred male individuals were assessed and divided in two groups: 50 field soccer players (AG) aged 18+0,7 years and 50 sedentary individuals (SG) aged 17,6+0,6 years. Groups were analyzed regarding body mass, height, body mass index (BMI), flexibility and fat percentage. Balance was assessed using the Dynamic Balance System protocol, level 8 of stability of the Biodex Balance System (BBS) equipment. RESULTS: Athletes presented better indexes in the dominant member in the test performed to the right (p=0,039), and in the non-dominant member in the test to backward/left (p=0,007). Sedentary individuals presented better indexes in the test performed to the right (p=0,034) in the non-dominant member. There was no statistical difference in the other tests. The SG presented better performance of the non-dominant member when compared to the dominant member in most of the tests performed. In the AG, there was a better performance of the non-dominant member in the overall stability index (p=0,027) and to the left (p=0,009). There was poor correlation between anthropometric measures and balance indexes measured by the BBS in both groups. CONCLUSIONS: There was no difference in postural balance between field soccer athletes and sedentary individuals. The dominance affected the unipodal balance of sedentary individuals, but not of field soccer athletes from the junior category. The anthropometric indexes did not interfere in the postural balance

Para minimizar as perturbações posturais de um movimento, o controle postural ativa os músculos não associados ao movimento focal. Os ajustes posturas de idosos são menos eficientes para evitar as quedas. O medo da queda também é um risco de queda. Deste modo, o problema desta pesquisa é: como o ajuste postural é organizado para garantir o controle postural durante atividade voluntária nos idosos caidores? Participaram 40 idosos (72,1±2,7 anos) que foram divididos em quatro grupos de acordo com suas características de queda e atividade física. Cada grupo (n=10) realizou a tarefa de flexão rápida dos membros superiores em bases de apoio instável e estável, as tarefas de alcance anterior e lateral e responderam a Falls Eficacy Scale. A atividade eletromiográfica dos músculos do tronco e do membro inferior foi registrada nos intervalos típicos dos ajustes posturais. A atividade muscular foi maior nas tarefas de alcance, no ajuste postural online, nos idosos caidores e sem medo de cair. Os idosos sedentários mostraram maior ativação dos músculos da cadeia anterior e os idosos ativos da mostraram maior ativação da musculatura posterior. A variabilidade do sinal eletromiográfico foi maior no ajuste postural compensatório, na tarefa sobre base instável, em idosos caidores. Conclue-se que os idosos caidores aumentam a atividade muscular após o início de movimento para manter o equilíbrio durante a tarefa pela incapacidade de gerar um APA eficiente. Os fatores de risco extrínsecos para quedas são relevantes para os idosos, uma vez que prática da atividade física não elimina o risco de cair / To minimize the postural disturbance provoked by a movement, the postural control activates the postural muscles instead of the focal movement muscles. The postural adjustments in the elderly are not enough efficient to avoid the falls. The fear of falling is also a risk of falling. Thus, the research question is: how the posture adjustment is organized to ensure postural control during voluntary activity of the falling elderly? The participants were 40 elderly (72.1 ± 2.7 years old) who were divided into four groups according to their falls characteristics and physical activity. Each group (n = 10) performed the shoulder extension as fast as possible on the unstable and stable suportt bases, as well the anterior and lateral reach task. They answered the Falls Eficacy Scale. The electrical activity of the trunk and lower limb muscles were recorded within the typical ranges of the postural adjustments. The highest muscle activation occurred during the reach tasks, for the online postural adjustment, for the fallers and without fear of falling. The sedentary participants showed higher activation of the anterior muscles and the active participants presented higher activation of the posterior muscles. The variability of electromyographical activity is higher during the compensatory postural adjustment, for the unstable support basis and for the fallers. It is concluded that the falling elderly increases the muscle activity after the beginning of movement to maintain balance due to the anticipatory postural adjustment inefficiency. The extrinsic risk factors to fall are relevant for falling prevention in elderly, since the practice of physical activity does not eliminates the risk to fall

A entorse de tornozelo pode ocorrer pela amplitude exagerada de inversão e flexão plantar. Lacuna importante no controle postural é a ação do ajuste postural antecipatório (APA) e compensatório (APC) para estabilizar a articulação do tornozelo. O reflexo de estiramento (M1) e as reações pré-programadas (M2 e M3) foram pouco exploradas em pessoas com instabilidade crônica de tornozelo (CAI). A co-ativação e inibição são fenômenos modulados em nível medular por neurônios excitatórios e inibitórios, mas as informações sobre esses fenômenos atuam na CAI são escassas. A fadiga muscular afeta negativamente as pessoas na condição de CAI. Logo, qual é a relação entre APA e APC no movimento de entorse de tornozelo? A CAI pode alterar as respostas M1, M2 e M3 por lesões osteomioarticulares do tornozelo? A fadiga pode alterar todas estas variáveis em pessoas com CAI? Esta dissertação de mestrado teve por objetivo geral analisar o sinal EMG no movimento simulado da inversão de tornozelo em atletas universitárias de futsal que possuem e que não possuem a CAI. A amostra foi composta por 24 atletas de futsal feminino universitário e foram divididos em dois grupos: controle e instabilidade. A simulação do movimento de entorse do tornozelo foi feita por meio de uma plataforma mecânica que simula o movimento de inversão de tornozelo. Foi utilizado um sistema de aquisição de sinais de 8 canais, onde foram utilizados 4 canais para registro EMG e 3 canais para o registro do sinal do acelerômetro. Para determinar o início e final do movimento da plataforma foi fixado um acelerômetro 3D em uma das bordas da plataforma de inversão. Foram realizar quedas aleatórias na plataforma de inversão antes e depois do protocolo de fadiga. Foram monitorados os músculos tibial anterior, fibular longo e curto e gastrocnêmio lateral. Os períodos analisados foram os APA, APC, reflexo de estiramento muscular e reações pré-programadas. Parece que durante os períodos M1, M2 e M3 há um fator de desproteção no grupo instabilidade, apesar de haver em alguns pares de músculos uma maior coerência, comparado com o grupo controle. Durante o APA os músculos eversores não foram alterados no grupo instabilidade, mas no APC os eversores foram menores comparados com o grupo controle, sugerindo um fator de desproteção. Na correlação cruzada, todos os pares de músculos foram maiores no grupo controle, uma forma de se opor ao movimento de inversão maior que o grupo instabilidade. A co-ativação e inibição recíproca foram alteradas com a fadiga, aumentando após a fadiga, mas a inibição recíproca foi maior somente no grupo controle, podendo mover a articulação do tornozelo de uma forma mais facilitada que o grupo instabilidade. A coerência de pares de músculos foi diferente somente nos grupos, sendo que durante o APC os músculos não sincronizaram de forma satisfatória no grupo instabilidade, somente durante APA e período M / Ankle sprain is an injury associated with sports and exercise and may be used for the exaggerated amplitude of inversion and plantar flexion. An important gap in postural control is the anticipatory (APA) and compensatory (CPA) postural adjustments to stabilize the ankle joint. The stretch reflex (M1) and the pre-programmed reactions (M2 and M3) were poorly explored in people with chronic ankle instability (CAI). Coactivation and recíprocal inhibition are phenomena modulated at the spinal level by excitatory and inhibitory neurons, but the information about these phenomena in CAI is scarce. Negative effects of muscular fatigue affect persons with CAI. Therefore, What is the relationship between APA and CPA in the movement of ankle sprain? Can CAI change the M1, M2 and M3 responses due to osteomyoarticular ankle injuries? Can fatigue change all these variables in people with CAI? This dissertation aimed at analysing the EMG signal in the simulated ankle inversion movement task in female indoor soccer university athletes who have and do not have the CAI. Participants were 24 female indoor soccer college athletes divided in two groups: control and instability. Simulation of ankle sprain was performed with a mechanical platform that simulated the ankle inversion movement. An 8-channel signal acquisition system was used, which 4 channels were used for EMG recording and 3 channels to record accelerometer signal. For determine the beginning and end of the movement of the inversion platform a 3D accelerometer was fixed to one of the edges of the inversion platform. We performed random falls on the inversion platform before and after the fatigue protocol. Muscles monitored were mm. tibialis anterior, fibularis longus, fibularis brevis and gastrocnemius lateralis. Data epochs were APA, CPA, muscle stretching reflex and preprogramed reactions. During M1, M2 and M3 epochs, there was an unprotection factor for instability group, although in some muscle pairs there were more coherence compared to control group. The eversor muscles were not changed in instability group compared with control group during APA epoch, it suggests an unprotect factor. All pair of muscles, the cross correlation were greater in control group to oppose the inversion movement greater in control group than instability group. Coactivation and reciprocal inhibition were changed with fatigue, increasing after fatigue, but reciprocal inhibition was greater only in control group, and could move the ankle joint more easily than for instability group. Coherence of muscle pairs was different only between groups, and during CPA the muscles did not synchronize satisfactorily for instability group, only during APA and M epochs

Para minimizar as perturbações posturais de um movimento, o controle postural ativa os músculos não associados ao movimento focal. Os ajustes posturas de idosos são menos eficientes para evitar as quedas. O medo da queda também é um risco de queda. Deste modo, o problema desta pesquisa é: como o ajuste postural é organizado para garantir o controle postural durante atividade voluntária nos idosos caidores? Participaram 40 idosos (72,1±2,7 anos) que foram divididos em quatro grupos de acordo com suas características de queda e atividade física. Cada grupo (n=10) realizou a tarefa de flexão rápida dos membros superiores em bases de apoio instável e estável, as tarefas de alcance anterior e lateral e responderam a Falls Eficacy Scale. A atividade eletromiográfica dos músculos do tronco e do membro inferior foi registrada nos intervalos típicos dos ajustes posturais. A atividade muscular foi maior nas tarefas de alcance, no ajuste postural online, nos idosos caidores e sem medo de cair. Os idosos sedentários mostraram maior ativação dos músculos da cadeia anterior e os idosos ativos da mostraram maior ativação da musculatura posterior. A variabilidade do sinal eletromiográfico foi maior no ajuste postural compensatório, na tarefa sobre base instável, em idosos caidores. Conclue-se que os idosos caidores aumentam a atividade muscular após o início de movimento para manter o equilíbrio durante a tarefa pela incapacidade de gerar um APA eficiente. Os fatores de risco extrínsecos para quedas são relevantes para os idosos, uma vez que prática da atividade física não elimina o risco de cair / To minimize the postural disturbance provoked by a movement, the postural control activates the postural muscles instead of the focal movement muscles. The postural adjustments in the elderly are not enough efficient to avoid the falls. The fear of falling is also a risk of falling. Thus, the research question is: how the posture adjustment is organized to ensure postural control during voluntary activity of the falling elderly? The participants were 40 elderly (72.1 ± 2.7 years old) who were divided into four groups according to their falls characteristics and physical activity. Each group (n = 10) performed the shoulder extension as fast as possible on the unstable and stable suportt bases, as well the anterior and lateral reach task. They answered the Falls Eficacy Scale. The electrical activity of the trunk and lower limb muscles were recorded within the typical ranges of the postural adjustments. The highest muscle activation occurred during the reach tasks, for the online postural adjustment, for the fallers and without fear of falling. The sedentary participants showed higher activation of the anterior muscles and the active participants presented higher activation of the posterior muscles. The variability of electromyographical activity is higher during the compensatory postural adjustment, for the unstable support basis and for the fallers. It is concluded that the falling elderly increases the muscle activity after the beginning of movement to maintain balance due to the anticipatory postural adjustment inefficiency. The extrinsic risk factors to fall are relevant for falling prevention in elderly, since the practice of physical activity does not eliminates the risk to fall

Neuromuscular fatigue, even that caused by light submaximal exercise, impairs motor performance and alters motor planning. This impairment is evident in muscle reaction time, force production capacity and joint position sense as well as in more complex tasks such as postural stability. When an individual is fatigued their postural sway increases and they are less able to recover from unexpected postural perturbations. Although a large number of work-related falls are caused by fatigue every year, the mechanisms behind the instability are not well understood. Since postural control does not require a large amount of muscular strength it is unclear whether the post-fatigue changes in posture are due to impairment within the muscle fibers or are a central modification of the motor plan used to execute the movement task. In order to better understand neuromuscular fatigue researchers have labeled fatigue occurring within the muscles ‘peripheral fatigue’ and that occurring within the central nervous system ‘central fatigue’. At the onset of a muscular contraction peripheral and central fatigue develop simultaneously, making it difficult to clearly articulate the role that they each play in the decreased motor performance found post-fatigue. Techniques such as transcranial magnetic and electrical nerve stimulation quantify the contribution of central fatigue to the decreased maximal force production but the impact on motor planning is still not well understood. Therefore, the primary aim of this doctoral dissertation was to isolate central fatigue from peripheral muscle fatigue and to compare the influence that it may have on dynamic postural control to the changes caused by general fatigue of the local postural muscles. This overarching research goal was accomplished through five separate studies. The first study in this dissertation determined that at least seven postural trials needed to be performed to ensure that the participants had fully adapted to the postural task before the fatigue protocol was implemented. Experiment 2 characterized the fatigue produced by bilateral, isometric ankle muscle contractions and examined the recovery of the central and peripheral changes throughout a ten-minute post-fatigue recovery period. The results demonstrated that the alternating maximal ankle plantar and dorsiflexor contractions created central and peripheral fatigue. Central fatigue recovered within the first two minutes post-fatigue while peripheral fatigue lasted throughout the ten-minute post-fatigue period. Experiment 3 analyzed the impact of this ankle muscle fatigue protocol on the postural response to a continual, externally driven, sinusoidal oscillation of the support platform. In this study the fatigued participants were able to stabilize their center of mass displacement using two different anticipatory postural responses to the backwards perturbation whereas all of the participants used the same anticipatory response to the forwards perturbation. All three postural responses became progressively more conservative throughout the ten-minute post-fatigue period, despite the rapid recovery of the ankle force production capacity. The final two studies characterized the fatigue produced during a continuous, isometric forearm contraction and assessed the impact on ankle motor performance (Experiment 4) and on postural control (Experiment 5). Peripheral fatigue created in the forearm muscles during this contraction remained throughout the post-fatigue testing session. Central fatigue and a decreased maximal force production capacity were quantified in both the forearm and ankle plantarflexor muscles immediately after the forearm contraction, indicating that central fatigue created during the forearm exercise crossed over to the distal and unrelated ankle plantarflexor muscles. The influence of the central fatigue created during the forearm contraction affected the anticipatory postural response in a similar way to the fatigue created by the ankle fatigue protocol. The post-fatigue modification of the postural response dissipated as the central fatigue recovered. Taken together, these five studies extend the current understanding of how exercise induced neuromuscular fatigue modifies the central nervous system’s control of complex motor tasks.