Introdução: No Karatê o chute frontal Mae geri é considerado uma técnica de simples execução, porém muito eficiente e muito utilizada em competições. Os fundamentos do Karatê descrevem que o melhor desempenho do chute será alcançado quando as forças de todas as partes do corpo forem utilizadas simultaneamente, do centro do corpo para as extremidades, o que parece ser suportado pelo princípio biomecânico de coordenação de impulsos parciais. Para que o chute seja eficiente e atinja a máxima velocidade, a transferência de energia mecânica entre os segmentos deve acontecer de tal maneira que os segmentos envolvidos no golpe se movimentem dentro de uma sequência no sentido proximal-distal. Objetivos: O presente estudo tem como objetivo geral avaliar parâmetros cinemáticos e cinéticos do Mae geri para compreender a dinâmica do golpe realizado por caratecas de diferentes níveis de treinamento. Método: Doze caratecas do grupo faixa preta (12,75 ± 8,91 anos de prática) e sete caratecas do grupo faixa branca (1,18 ± 0,88 anos de prática) executaram o Mae geri. Com os dados de cinemática dos segmentos (pelve, coxa, perna e pé) do membro inferior de ataque e de força de reação do solo foram calculadas as velocidades lineares, velocidades angulares, os torques, as potências e as transferências de energia entre os segmentos. Resultados: No grupo faixa preta as magnitudes de velocidade linear dos segmentos foram significativamente maiores do que no grupo faixa branca, resultando em menor duração total do golpe no grupo faixa preta. O Mae geri do grupo faixa preta é caracterizado no início do golpe por uma transferência de energia mecânica dos segmentos distais para os segmentos proximais de todas articulações analisadas (quadril, joelho e tornozelo), com maior magnitude de energia mecânica sendo transferida do pé para a perna, ainda com o pé no chão. Após tirar o pé de ataque do chão, a transferência de energia mecânica da coxa para a pelve apresenta um aumento de magnitude. No último terço do golpe, há uma transferência de energia mecânica da perna para a coxa na articulação do joelho e da perna para o pé na articulação do tornozelo. O grupo faixa branca tem um comportamento diferente de transferência de energia mecânica entre os segmentos comparado ao grupo faixa preta, principalmente no último terço do golpe. Além disso, magnitudes de geração de potência pelos músculos para os segmentos, de absorção de potência pelos músculos a partir dos segmentos e transferência de energia mecânica entre segmentos foram significativamente maiores no grupo faixa preta. Conclusão: Os resultados sugerem que a transferência de energia mecânica entre os segmentos permite que caratecas faixa preta executem o Mae geri de acordo com os princípios biomecânicos de coordenação dos impulsos parciais, respeitando uma sequência de movimentos no sentido proximal-distal. O nível de treinamento dos caratecas implica em diferenças no comportamento das velocidades dos segmentos e na transferência de energia entre os segmentos, o que influencia na eficiência e no desempenho do golpe / Introduction: In karate the Mae geri front kick is considered a simple execution technique, however very efficient and widely used in competitions. The karate\'s fundamentals describe that the best kick performance will be achieved when the strengths of all parts of the body are used simultaneously, from the body\'s center to outside, which seems to be supported by the biomechanical principle of partial impulse coordination. In order for the kick to be efficient and reach maximum speed, the mechanical energy transfer between segments must occur in such a way that the segments involved in the stroke move within a sequence in the proximal-distal direction. Purpose: The present study has as general purpose to evaluate kinematic and kinetic parameters of the Mae geri to understand the dynamics of the stroke made by karate practitioners of different levels of training. Method: Twelve karate practitioners of black belt group (12,75 ± 8,91 years of practice) and seven karate practitioners of white belt group (1,18 ± 0,88 years of practice) performed the Mae geri. With the kinematics data of the segments (pelvis, thigh, leg and foot) of the lower attack member and the ground reaction force were calculated the linear velocities, angular velocities, the moments of force, the powers and the mechanical energy transfer between segments. Results: At black belt group the linear velocity magnitudes of segments were significantly higher than in the white belt group, resulting in a shorter total stroke duration in the black belt group. The Mae geri of the black belt group is characterized at the beginning of the stroke by a transfer of mechanical energy from the distal segments to the proximal segments of all joints analyzed (hip, knee and ankle), with higher magnitude of mechanical energy being transferred from the foot to the leg, still with the foot on the ground. After removing the attack foot on the ground, the mechanical energy transfer from the thigh to pelvis presents an increase of magnitude. At the last third of the stroke, there is a mechanical energy transfer from the leg to the thigh at the knee joint and from the leg to the foot at the ankle joint. The white belt group has a different behavior of mechanical energy transfer between the segments compared to the black belt group, specially at the last third of the stroke. Besides that, magnitudes of power generation by the muscles to the segments, power absorption by the muscles from the segments and mechanical energy transfer between segments were significantly higher in the black belt group. Conclusion: The results suggest that the transfer of mechanical energy between segments allows black belt karate practitioners perform the Mae geri according to the biomechanical principles of the coordination of partial impulses, respecting a sequence of movements in the proximal-distal direction. The training level of the karate practitioners implies in differences in the behavior of the velocities of the segments and in the mechanical energy transfer between segments, which influences the efficiency and the performance of the stroke

The major objective of this thesis was to investigate how the use of a recently developed microprocessor-controlled limb system altered the negative mechanical work done by the intact and prosthetic limb when trans-femoral amputees terminated gait. Participants terminated gait on a level surface from their self-selected walking speed and on declined surface from slow and customary speeds, using limb system prosthesis with microprocessor active or inactive. Limb negative work, determined as the integral of the negative mechanical (external) limb power during the braking phase, was compared across surface, speed and microprocessor conditions. Halting gait was achieved predominantly from negative work done by the trailing/intact. Trailing versus leading limb mechanical work imbalance was similar to how able body individuals halted gait. Importantly, the negative limb work performed on the prosthetic side when terminating gait on declined surface was increased when the microprocessor was active for both slow and customary speeds (no difference on level surface) but no change on intact limb. This indicates the limb system’s ‘ramp-descent mode’ effectively/dynamically altered the hydraulic resistances at the respective joints with evidence indicating changes at the ankle were the key factor for increasing the prosthetic limb negative work contribution. Findings suggest that trans-femoral amputees became more assured using their prosthetic limb to arrest body centre of mass velocity when the limb system’s microprocessor was active. More generally findings suggest, trans-femoral amputees should obtain clinically significant biomechanical benefits from using a limb system prosthesis for locomotion involving adapting to their everyday walking where adaptations to an endlessly changing environment are required. / Higher Committee of Education Development in IRAQ (HCED)

La problématique du port de charges par l’Homme est l’objet de questionnements scientifiques depuis plus d’un siècle, notamment dans les armées où les soldats doivent remplir des objectifs opérationnels tout en emportant des équipements lourds, distribués de façon complexe autour de leur corps, et cela au cours d’efforts allant de quelques heures à plusieurs jours. Aussi, avec le développement des nouvelles technologies et l’arrivée des systèmes fantassins futurs sur le marché de la défense, cette problématique continue de se complexifier puisque la masse totale emportée tend encore à croître. Objectif général : Le but de ce travail de thèse était d’étudier l’impact biomécanique, métabolique et neuromusculaire du port d’un système fantassin moderne chez le soldat expérimenté. Plus précisément, une première recherche a été menée pour caractériser les effets aigus du port d’un tel équipement sur la biomécanique et le coût métabolique de la marche. Puis, une seconde recherche a été consacrée à l’étude des conséquences neuromusculaires et locomotrices d’une mission militaire (simulation sur le terrain) de durée « extrême » réalisée avec ce système fantassin moderne. Première partie : L’analyse de la marche sur tapis roulant dynamométrique a permis de montrer que le port du système fantassin en configurations de « combat » et de « marche d’approche » (principales configurations du théâtre militaire, représentant respectivement ~30 % et ~50 % de la masse corporelle des sujets) altérait le pattern spatio-temporel par rapport à la marche sans charge. Par ailleurs, le travail mécanique appliqué au centre de masse et le coût métabolique de la marche augmentaient parallèlement lors du port des deux configurations du système fantassin, ce qui résultait en un maintien du rendement locomoteur constant dans toutes les conditions testées. Le mécanisme de transfert d’énergie en pendule inversé (méthode Cavagna), permettant de minimiser les coûts mécanique et métabolique de transport, était également similaire dans toutes les conditions avec et sans charge. Enfin, bien que complexement organisés autour du corps du soldat, les équipements militaires n’induisaient pas d’effets mécaniques et métaboliques sensiblement plus importants que ceux rapportés lors du port de masses positionnées symétriquement autour de la taille ; ce mode de portage étant pourtant considéré comme l’un des plus optimisés, abstraction faite des techniques de portage sur la tête inadaptées au contexte militaire. Deuxième partie : La réalisation d’une mission simulée, incluant 21 h d’activités militaires sur le terrain et le port constant d’un système fantassin, résultait en une fatigue neuromusculaire (mesure des forces, électrostimulation et EMG) relativement modérée des muscles locomoteurs extenseurs du genou et fléchisseurs plantaires chez les soldats expérimentés inclus dans ce travail. Les origines de cette fatigue neuromusculaire étaient essentiellement périphériques, mais s’accompagnaient d’une fatigue subjective importante. Enfin, la réalisation de la mission, et donc la fatigue des muscles locomoteurs notamment associée à cette dernière, n’affectait pas sensiblement les paramètres mécaniques et métaboliques de la marche. Conclusion générale : Ce travail rapporte les premières données relatives aux effets biomécaniques, métaboliques et neuromusculaires du port d’un système fantassin moderne chez le soldat expérimenté, et ce par le biais d’une simulation opérationnelle visant à reproduire les conditions militaires / For more than a century, load carriage has been the source of many scientific questions and researches, especially in armies in which soldiers have to reach operational goals while carrying heavy loads complexly distributed around their body and this for some hours to several days. Moreover, with the development of new technologies and the advent of land warfare systems, this issue is becoming more complex since load continues to increase. General purpose: The aim of the present work was to investigate the biomechanical, metabolic and neuromuscular constraints imposed by the carriage of a modern land warfare system in experienced soldiers. Specifically, a first study was conducted to characterize the acute effects of land warfare equipments carriage on the biomechanics and energetics of walking. Moreover, a second research was performed to investigate the neuromuscular and locomotor consequences of an extreme-duration simulated military mission (performed in the field) involving the carriage of these specific equipments. First part: Walking analyses performed on an instrumented treadmill showed that the carriage of a land warfare system in two configurations made for “Battles” and “Road marches” (main configuration used in the field representing ~30% and ~50% of subject’s body mass, respectively) altered the walking pattern. Moreover, the mechanical work applied to the center of mass increased in parallel with the energy cost of walking during Battle and Road March configurations carriage, as shown by the constant locomotor efficiency in the three tested conditions. The inverted pendulum-like energy exchange (Cavagna’s standard method), allowing mechanical/metabolic energy saving, was also constant in all the unloaded and loaded conditions. Finally, even if the load was complexly distributed around soldiers’ body with this warfare system, this did not induce greater effects than those reported with loads carried symmetrically around the waist and close to the center of mass; which has yet been hypothesized to be the optimal method of load carriage from both mechanical and metabolic standpoints (except “original” methods such as head carrying that cannot be used in the military theater). Second part: Performing a 21-h simulated military mission with heavy land warfare system carriage induced relatively moderate neuromuscular alterations (isometric force measurement with electrical stimulation and EMG) for both knee extensors and plantar flexors locomotor muscle groups in experienced soldiers. Moreover, the origin of fatigue was essentially peripheral for both muscle groups but was concomitant with a large sensation of fatigue. Finally, the simulated mission, and notably the associated locomotor muscles fatigue, did not alter walking biomechanics and energetics. General conclusion: These results bring the first insight into the biomechanical, metabolic and neuromuscular consequences of modern land warfare system carriage in experienced soldiers, and this by a real-world approach aiming at simulating the military theater conditions

En prenant comme point d’horizon l’entrée du concept de travail mécanique dans la physique théorique par les ingénieurs-savants du début de 19e siècle (Coriolis et Navier notamment), cette thèse montre la filiation de ce concept vis-à-vis de démarches apparaissant à l’aube du 18e siècle à l’Académie Royale des Sciences de Paris, notamment dans les oeuvres d’Amontons et de Parent. La thèse montre alors comment et pourquoi le concept commence à se développer au premier 18e siècle dans cet environnement, comment il est ensuite repris, enrichi, modifié par Pitot, Bélidor, Desaguliers, D. Bernoulli, et comment au contraire ce concept semble ignoré de savants plus théoriciens tel que D’Alembert. Le rôle de la rupture de la vision statique de la machine semble déterminant. Apparaît alors la forte dépendance de ce concept aux problématiques qu’il permet de résoudre, axées sur la quantification et l’optimisation de l’effet des hommes, des animaux et des machines en situation laborieuse, et leurs comparaisons mutuelles dont l’une des finalités est la recherche du profit économique. L’histoire du concept se donne à voir comme une interface permanente entre mécanique théorique, mécanique pratique, et aspects productifs. On suggère alors que la légitimité du concept tient dans sa pertinence à rendre compte du travail des agents producteurs. Enfin, la thèse s’attache à recréer l’épaisseur du réel derrière les concepts et les problématiques, en montrant ce qu’ils doivent aux stratégies gouvernementales et aux pratiques d’ingénieurs. / Taking the early 19th century concept of mechanical work in theoretical physics (popular among such engineers as Coriolis and Navier) as the point of reference, this essay draws a connection between this concept and similar reasoning occurring at the Royal Academy of Sciences in Paris at the turn of the 18th century, especially evident in the works of Amontons and Parent. The essay then demonstrates how and why this concept begins to develop in this academic environment, and how it is then adopted, enhanced and modified by Pitot Bélidor, Désaguliers, and D. Bernoulli while seemingly ignored by theorists such as D’Alembert. The role of the breakdown of the conceptualisation of machines as static agents seems decisive. What follows is a strong dependence on the concept of mechanical work for its ability to problem solve and in pursuit of economic gain, particularly as pertains to quantification, optimization and the comparative labour productivity of men, animals and machines. The concept’s history suggests a permanent interplay between theoretical mechanics, practical mechanics and productivity, thus indicating that the legitimacy of the concept lies in its ability to represent the work of producing agents. Finally, the essay attempts to recreate in practical terms the reality behind the concepts and problems, showing what they owe to government strategies and what to the practices of engineers.