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Stürze sind weltweit die zweithäufigste Ursache für Verletzungen und Todesfälle, und stellen eine massive Belastung für jedes Gesundheitssystem dar. Die meisten Stürze resultieren aus einer fehlgeschlagenen Reaktion auf unerwartete Störungen der Fortbewegung, wie z. B. Stolpern oder Ausrutschen. Unter den vielen bestehenden Interventionsmodellen, die auf das Risiko von Stürzen abzielen, sind bewegungsbasierte Interventionen die kosteneffektivsten. Da bei den meisten Trainingsansätzen die verbesserte Gleichgewichtsfähigkeit nur begrenzt auf untrainierte Situationen übertragen werden kann, müssen Faktoren, wie die Retention und die Dosis-Wirkungs-Beziehung noch ermittelt werden. Des Weiteren sind die Mechanismen, welche den wirksamen Trainingsmaßnahmen zugrunde liegen, noch nicht vollständig erforscht. Training der grundlegenden Mechanismen zur Wiederherstellung des Gleichgewichts (d. h. die Gegenrotation von Körpersegmenten und die Modulation der Unterstützungsfläche) unter instabilen Bedingungen, sowohl unter den trainierten Bedingungen als auch unter unbekannten Bedingungen, verbessert. Darüber hinaus erhöhte dieses Training die kraftgenerierende Kapazität der Muskeln der unteren Extremitäten, was die Ausführung von Gleichgewichtswiederherstellungsreaktionen weiter fördert. Auf der Grundlage dieser vielversprechenden Ergebnisse versucht diese Arbeit, Kenntnisse über die zugrundeliegenden neuromechanischen Anpassungen dieses vorteilhaften Trainingsansatzes, zu liefern. Robustheit kann als Folge verschiedener Modulationen von Muskelsynergien entstehen. Die Wahl der Strategie von Faktoren wie der Ausprägung der Störung, sowie der Ausprägung und Beschränkungen der Bewegungsaufgabe, und der wahrgenommenen Herausforderung für das Gleichgewicht bestimmt wird. Außerdem erhöht das Training auf instabilen Oberflächen nicht per se die mechanischen Anforderungen an die Beinmuskulatur. Die Zunahme der Muskelkraft scheint daher eine Folge neuronaler Anpassungen zu sein. / Falls are the second leading cause of unintentional injury and death worldwide. Among manifold causes, most fall result from a failed response to unexpected perturbations such as a trip or slip. Fall-related injuries can significantly impair quality of life, and their consequences represent a massive burden for any healthcare system. Amid fall prevention paradigms, exercise-based interventions are the most cost-effective. However, most training approaches have a limited transfer to untrained situations and the underlying mechanisms of effective training interventions are still not fully understood. Training the execution of the fundamental balance recovery mechanism (i.e., counterrotating body segments and increasing the base of support) in the presence of perturbations has been reported as an alternative capable of improving balance recovery performance in both trained and non-trained situations and of increasing the force capacity of the lower limb, further promoting the execution of balance recovery reactions. Based on these promising results, this thesis endeavours to provide insight into the fundamental elements promoting the neuromechanical adaptations underpinning the reported advantages of this training paradigm. The analysis of the neuromuscular responses to unstable surfaces during a training session revealed different strategies to cope with perturbations and increase robustness. These different modulations of muscle synergies depend on several factors such as the characteristics of the task and the individual capacities. Moreover, training on unstable surfaces did not increase the mechanical demands upon the leg muscles per-se. Thus the gains in muscle force observed after training the fundamental mechanism of balance recovery onto unstable surfaces are likely a consequence of neural adaptations.

A forward dynamic model was developed to predict the performance of Spinal Cord Injured (SCI) individuals cycling an isokinetic ergometer using Neuromuscular Electrical Stimulation (NMES) to elicit contractions of the quadriceps, hamstring and gluteal muscles. Computer simulations were performed using three inter-connected models: a kinematic model of segmental linkages, a muscle model predicting forces in response to stimulation, and a kinetic model predicting ergometer pedal forces resulting from muscle stimulation. Specific model parameters for SCI individuals were determined through measurements from isometric and isokinetic contractions of the quadriceps muscles elicited using surface stimulation. The muscle model was fitted to data resulting from these isolated experiments in order to tailor the model's parameters to characteristics of muscles from SCI individuals. Isometric data from a range of knee angles were used to fit tendon slack lengths to the rectus femoris and vastus muscles. Adjustments to the quadriceps moment arm function were not able to improve the match between measured and modelled knee extension torques beyond those using moment arms taken from available literature. Similarly, literature values for constants from the muscle force - velocity relationship provided a satisfactory fit to the decline in torque with angular velocity, and parameter fitting did not improve this fit. Passive visco-elastic resistance remained constant for all velocities of extension except the highest (240 deg/s). Since knee angular velocities this high were not experienced during cycling, a visco-elastic dampener was not included within the present cycling model. The rise and fall in torque following NMES onset and cessation were used to fit constants to match the rate of change in torque. Constants for the rise in torque following NMES onset were significantly altered by changes in knee angle, with more extended angles taking longer for torque to rise. This effect was small, however, within the range of angles used during cycling, and consequently was not included within the cycling model. The decline in torque after NMES cessation was not affected by knee angle. A period of five minutes cyclical isometric activity of the quadriceps resulted in torque declining by more than 75% from rested levels. The activation time constants were largely unaffected by this fatigue, however, with only a small increase in the time for torque to decline, and no change in rise time or the delay between stimulation changes and resulting torque changes. The cycling model, therefore, did not incorporate any effect for changes in activation timing with fatigue. Performance of the full model was evaluated through measurements taken from SCI individuals cycling a constant velocity ergometer using NMES elicited contractions of the quadriceps, hamstring and gluteal muscles. Pedal transducers measured forces applied to the pedals for comparison between measured and modelled values. A five minute period of continuous cycling using just the quadriceps muscles produced similar results to those found for isolated knee extension. External power output dropped by 50% over the five-minute period, however there was no change in the pattern of torque production with fatigue. Cycling experiments were conducted using single muscle groups across a range of NMES firing angles. Experimental protocols were designed to seek the firing angles for each muscle that maximised power output by that group. Changes in power output in response to firing angle changes were not large, however, in comparison to the effects of cumulative fatigue and inconsistent power output between trials. This lead to large uncertainties in the determination of those firing angles that maximised power output by each muscle. Results suggest that NMES firing angles to maximise power output by the quadriceps muscles were relatively similar for each subject. For the hamstring muscles, however, substantial differences were observed in the range of firing angles that maximised power output. Results for the gluteal muscles were variable, with some subjects not applying any measurable torque to the cranks, even with maximal stimulation applied. The model produced a good match to experimental data for the quadriceps muscles, both in the shape of pedal force curves and the firing angles that maximised external power output. The individual variability in hamstring responses was not, however, predicted by the model. Modification of the relative size of the hamstrings' moment arms about the hip and knee substantially improved the match between measured and modelled data. Analysis of results suggests that individual variability in the relative size of these moment arms is a major cause of variation in individual's response to hamstring stimulation. There were apparent limitations in the model's ability to predict the shape of crank torques resulting from stimulation of the gluteus maximus muscle. It is suggested that further research be conducted to enable modelling of this muscle using a range of fibre lengths and moment arms.

A forward dynamic model was developed to predict the performance of Spinal Cord Injured (SCI) individuals cycling an isokinetic ergometer using Neuromuscular Electrical Stimulation (NMES) to elicit contractions of the quadriceps, hamstring and gluteal muscles. Computer simulations were performed using three inter-connected models: a kinematic model of segmental linkages, a muscle model predicting forces in response to stimulation, and a kinetic model predicting ergometer pedal forces resulting from muscle stimulation. Specific model parameters for SCI individuals were determined through measurements from isometric and isokinetic contractions of the quadriceps muscles elicited using surface stimulation. The muscle model was fitted to data resulting from these isolated experiments in order to tailor the model's parameters to characteristics of muscles from SCI individuals. Isometric data from a range of knee angles were used to fit tendon slack lengths to the rectus femoris and vastus muscles. Adjustments to the quadriceps moment arm function were not able to improve the match between measured and modelled knee extension torques beyond those using moment arms taken from available literature. Similarly, literature values for constants from the muscle force - velocity relationship provided a satisfactory fit to the decline in torque with angular velocity, and parameter fitting did not improve this fit. Passive visco-elastic resistance remained constant for all velocities of extension except the highest (240 deg/s). Since knee angular velocities this high were not experienced during cycling, a visco-elastic dampener was not included within the present cycling model. The rise and fall in torque following NMES onset and cessation were used to fit constants to match the rate of change in torque. Constants for the rise in torque following NMES onset were significantly altered by changes in knee angle, with more extended angles taking longer for torque to rise. This effect was small, however, within the range of angles used during cycling, and consequently was not included within the cycling model. The decline in torque after NMES cessation was not affected by knee angle. A period of five minutes cyclical isometric activity of the quadriceps resulted in torque declining by more than 75% from rested levels. The activation time constants were largely unaffected by this fatigue, however, with only a small increase in the time for torque to decline, and no change in rise time or the delay between stimulation changes and resulting torque changes. The cycling model, therefore, did not incorporate any effect for changes in activation timing with fatigue. Performance of the full model was evaluated through measurements taken from SCI individuals cycling a constant velocity ergometer using NMES elicited contractions of the quadriceps, hamstring and gluteal muscles. Pedal transducers measured forces applied to the pedals for comparison between measured and modelled values. A five minute period of continuous cycling using just the quadriceps muscles produced similar results to those found for isolated knee extension. External power output dropped by 50% over the five-minute period, however there was no change in the pattern of torque production with fatigue. Cycling experiments were conducted using single muscle groups across a range of NMES firing angles. Experimental protocols were designed to seek the firing angles for each muscle that maximised power output by that group. Changes in power output in response to firing angle changes were not large, however, in comparison to the effects of cumulative fatigue and inconsistent power output between trials. This lead to large uncertainties in the determination of those firing angles that maximised power output by each muscle. Results suggest that NMES firing angles to maximise power output by the quadriceps muscles were relatively similar for each subject. For the hamstring muscles, however, substantial differences were observed in the range of firing angles that maximised power output. Results for the gluteal muscles were variable, with some subjects not applying any measurable torque to the cranks, even with maximal stimulation applied. The model produced a good match to experimental data for the quadriceps muscles, both in the shape of pedal force curves and the firing angles that maximised external power output. The individual variability in hamstring responses was not, however, predicted by the model. Modification of the relative size of the hamstrings' moment arms about the hip and knee substantially improved the match between measured and modelled data. Analysis of results suggests that individual variability in the relative size of these moment arms is a major cause of variation in individual's response to hamstring stimulation. There were apparent limitations in the model's ability to predict the shape of crank torques resulting from stimulation of the gluteus maximus muscle. It is suggested that further research be conducted to enable modelling of this muscle using a range of fibre lengths and moment arms.

Questions of preservation and promotion of health of students are highly relevant at the present time. Therefore now updating of forms and methods of physical education students is especially important. Also there is a need in the formation of students' priorities, a healthy lifestyle, an increase in the mode of motor activity and development programs, which will satisfy the needs of students, increase motivation and interest in physical culture. To improve the process of physical education at university should be used modern and the most popular types of motor activity in the health and fitness classes, which based on various fitness programs and adapted for students of special medical group. One of the varieties physical activity is pilates. It is popular now. People of different age and sex as well as with different levels of physical training can engage pilates. / Вопросы сохранения и укрепления здоровья студентов являются весьма актуальными в настоящее время. В связи с этим сейчас особенно важно обновление форм и методов работы по физическому воспитанию студентов. Также назрела необходимость в формировании у студентов приоритетов здорового образа жизни, увеличения режима двигательной активности и разработка программ, которые удовлетворяют потребности студентов, повысят мотивацию и интерес к занятиям физической культурой. С целью совершенствования процесса физического воспитания в вузе необходимо использовать на физкультурно-оздоровительных занятиях современные, наиболее популярные виды двигательной деятельности, которые основаны на различных фитнес - программах и адаптированы для студентов отнесённых к специальной медицинской группе. Одной из разновидностей фитнес-тренировки является пилатес, он достаточно популярен в настоящее время. Пилатесом могут заниматься люди разного возраста и пола, а также с разным уровнем физической подготовки.

Résumé : Le rôle du réseau veineux est central dans la fonction cardiovasculaire, pourtant, au regard de la littérature scientifique, il apparaît comme le« parent pauvre » comparé au cœur ou au réseau artériel. Ce constat vaut aussi bien pour la compréhension de l'hémodynamique veineuse que pour l'analyse physiopathologique de la maladie veineuse chronique en général et plus particulièrement lorsque le lien est fait avec la situation d'exercice. Nos différentes investigations avaient pour buts d'une part de mieux comprendre les adaptations du système veineux lors de l'activité physique et lors de la phase de récupération post-exercice et d'autre physiopathologiques de l'hyper pression veineuse sur la microcirculation chez le sujet atteint d'une pathologie veineuse. Ils ont également apporté une meilleure compréhension de la phase de récupération post-exercice et des effets bénéfiques des méthodes de récupération sur la performance et sur les adaptations vasculaires. L'interdépendance entre les différents secteurs (cœur, artères, microcirculation, veines) du système cardiovasculaire est un élément essentiel mis en évidence dans nos différents travaux. Ainsi, nous avons démontré que l'hémodynamique veineuse ne pouvait être analysée de manière isolée, mais au contraire part d'évaluer l'impact de la maladie veineuse chronique sur l'activité physique et réciproquement. Pour cela nous avons étudié les effets aigus de l'activité physique sur le fonctionnement de l'hémodynamique veineuse (évaluation de la pompe veineuse surale), et les effets de différentes méthodes de récupération (compression, immersion, électro stimulation neuro musculaire). Par ailleurs nous avons exploré les conséquences de la pathologie veineuse sur la réalisation d'une activité physique à travers l'analyse de la claudication veineuse. Les principaux résultats de nos travaux ont permis de mieux appréhender les adaptations de l'hémodynamique veineuse liées à l'exercice chez le sujet sain d'une part et de mieux comprendre les conséquences qu'elle devait être évaluée dans sa globalité, en mesurant les implications sur le remplissage cardiaque en aval et sur les échanges au niveau tissulaire en amont, et en recherchant la part du réseau splanchnique et celle du réseau des membres aux propriétés bien différentes sur le retour veineux systémique. En conclusion, nous avons comblé une partie des lacunes de la littérature en permettant une meilleure appréhension des relations veines, exercice physique, récupération et pathologie veineuse. Cependant, des interrogations persistent concernant la méthodologie à mettre en place pour l'évaluation du réseau veineux et les effets chroniques de la pratique intensive d'une activité physique sur la maladie veineuse chronique. / The role of the venous system is central to cardiovascular fonction, yet, in terms of scientific literature, it appears to be the "poor relation" compared to the heart or arterial system. This is true both for the physiological understanding of venous hemodynamics and for the pathophysiological analysis of chronic venous disease and more particularly when the link is made with exercise. The aim of our investigations was to better understand the adaptations of the venous system during physical activity and during the post-exercise recovery period and, to evaluate the impact of chronic venous disease on physical activity and vice versa. We have studied the acute effects of physical activity on venous hemodynamics (evaluation of the calf venous pump), and the effects of various recovery methods ( compression, immersion, calf low frequency electrical stimulation), and we have also explored the consequences of chronic venous disease upon physical activity through the analysis of venous claudication. The main results of our work enabled a better understanding of the adjustments in venous hemodynamics linked to exercise in healthy subjects and to better understand the pathophysiological consequences of high venous pressure on the microcirculation of patients with chronic venous disease. Our findings also provide a detailed understanding of venous hemodynamics during post-exercise recovery and the positive effects of recovery methods on both performance and vascular adjustments. The interdependence of the different organs and tissues (heart, arteries, microcirculation, veins) of the cardiovascular system is an essential element highlighted in this work. Thus, we demonstrated that venous hemodynamics could not be analyzed in isolation, but rather that it should be assessed as a whole by measuring implications on cardiac filling and on tissue exchange, and looking for the part of the splanchnic system and limbs system on systemic venous return. ln conclusion, we have filled some of the gaps in the literature by examining the relationships between veins, physical exercise, recovery and venous pathology. However, questions remain regarding the methodology to be implemented for the evaluation of the venous system and the chronic effects of the intensive physical activity practice on the chronic venous disease prevalence