Lower limb injury incidence is high amongst Royal Marine recruits. Tibial and metatarsal stress fractures are particularly problematic. The regular load carriage activities undertaken throughout training have been implicated, but mechanisms by which these injuries develop are poorly understood. The aim of this thesis was to improve understanding of the mechanisms by which the most prevalent Royal Marine training injuries develop. The first experimental chapter was a prospective study of 1065 Royal Marine recruits. Anthropometric and dynamic biomechanical variables (during barefoot running at 3.6 m.s-1) were recorded at the start of training. A smaller calf girth and bimalleolar breadth were found to predispose recruits to tibial stress fractures and ankle inversion injuries. Recruits who sustained tibial stress fractures demonstrated greater heel loading than those who remained injury-free. Recruits who sustained metatarsal stress fractures demonstrated later peak metatarsal pressures than those who remained injury-free. A review of the 32-week Royal Marine recruit training programme found an association between prolonged load carriage activities and injury occurrence. The second experimental study identified gait changes following a prolonged load carriage activity (12.8 km, 35.5 kg load). Biomechanical variables were recorded during barefoot running (3.6 m.s-1) in 32 recruits pre- and post-activity. Recruits demonstrated increased rearfoot loading, and later peak metatarsal pressures post-activity, indicative of a reduced ability to push-off. The final study examined the influence of the same load carriage activity on gait changes during walking (1.4 m.s-1) in 32 recruits, allowing assessment of the independent influence of load carriage. Kinetic and electromyographic variables provided further explanation of changes observed in the previous study. During load carriage there were increased plantar flexor and knee extensor moments and corresponding increases in muscle activity. There were reduced knee extensor moments, and evidence of plantar flexor muscle fatigue post-activity. A reduced ability to push off during stance due to muscular fatigue was suggested as a key contributor to tibial and metatarsal stress fracture development. This may explain the association between a smaller calf girth and tibial stress fracture development.

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Conversely, AA lost femoral neck BMD over the winter and this was not recovered over the summer, although the increase in width of the femoral neck may have partly compensated BMD loss to maintain strength in bending. The final prospective analysis was conducted in a separate sample of female athletes who were diagnosed with a stress fracture injury. The aim of this analysis was to determine the magnitude and time scale of bone loss following a stress fracture injury and subsequent regain following retaining. A group of 4 stress fracture cases and 3 controls were followed for a period of 6-8 months following a stress fracture injury. BMD and BMC (lumbar spine, femoral neck, and trochanter) and estimations of geometric properties CSA, Z and buckling ratio) were assessed using DXA. The mean difference of bone loss and bone regain was determined by BMD, BMC and geometric parameters from baseline to 6-8 weeks and 6-8 weeks to 6-8 months respectively. No significant bone loss was found in either cases or controls from baseline to 6-8 weeks at any of the bone parameters. A significant difference at the femoral neck was found in the injured leg of the stress fracture cases from 6-8weeks to 6-8months (mean (SE) 1.042(0.102) to 1.070(0.102) g/cm2, p=0.004) with no significant change in the contra-lateral case leg 1.036 (0.102) to 1.054(0.109) g/cm2). No significant bone regain was found in the control subjects (health or injured legs ). Thus athletes do not seem to lose significant BMD during the recovery phase of training when partial weight bearing is required. Subsequent bone regain above the initial baseline value does seem to occur in the injured leg within 8 months following the stress fracture once training is resumed. In conclusion the work within this thesis has not only reinforced previous stress fracture findings, showing that a history of stress fracture is increased in athletes with a history of amenorrhoea, but has identified novel results indicating a lower incidence of stress fracture in female endurance athletes than previously reported. Exercise cognitions have been identified as risk factors for stress fracture history independent of menstrual dysfunction. Furthermore and potentially the most novel finding of this research is the importance for the examination of bone geometric properties in amenorrhoeic athletes. Findings suggest that possible structural adaptations counteract the effects of low BMD and annual losses of BMD during seasonal training in amenorrhoeic endurance athletes. In light of these findings this thesis highlights scope for further longitudinal research in the area of structural adaptation to bone in amenorrhoeic athletes. Keywords: Stress fracture, bone mineral density, bone geometry, endurance athletes, menstrual dysfunction, eating and exercise cognitions.

Due to their prevalence and associated high rehabilitation costs, this thesis aimed to better understand factors influencing the risk of tibial (TSF) and third metatarsal (MT3SF) stress fractures in Royal Marine recruit training. In Study 1, the standard issue combat assault boot and neutral trainer were assessed during running. Running in the boot caused restricted ankle motion, greater forefoot loading, greater ankle stiffness and a more laterally applied horizontal force vector at the instant of peak braking, suggesting that the risk of incurring MT3SF was greater in this condition. In Study 2, bending stresses were modelled along the length of the third metatarsal of five participants, using individual bone geometry and dynamic gait data. Stresses were modelled for running when barefoot, and when shod in the standard issue footwear. Estimated peak bending stresses were significantly greater in the combat assault boot than the gym trainer, predominantly due to increased plantar loading. Individual bone geometry was however dominant in determining peak bending stresses. In Study 3, a large (n=1065) prospective study was conducted to identify differences in baseline characteristics between recruits sustaining a TSF or MT3SF and those who complete training uninjured. Ten TSF and 14 MT3SF cases were compared to 120 uninjured legs. Results suggest that risk of TSF is greater in those recruits with reduced ability to resist loading and attenuate impact during gait. Results for MT3SF suggest that ankle and foot position at touchdown, and the timing and magnitude of forefoot loading, are important factors influencing risk of this injury. The observation of lower age and BMI in both stress fracture groups was linked to lower bone strength and earlier fatigue mechanisms. This thesis has increased the understanding of MT3SF in particular, and provides information on specific factors which may be associated with MT3SF and TSF in RM recruits during basic training.

Marathon runners are prone to femoral stress fractures due to the high magnitudes and frequencies of lower extremity loads during training. Female runners tend to have a greater incidence of stress fracture compared to male runners. Sex-specific differences in body structure, joint pressure, and muscle activation patterns that influence bone remodeling may cause this observed difference in stress fracture occurrence. The goal of this thesis was to develop a finite element model of the femur during marathon training, then determine if marathon training affected bone properties of male and female runners differently. To achieve this goal, a finite element femur model was integrated with a bone remodeling algorithm. Sex-specific muscle and joint pressure loads corresponding to baseline activity and marathon training were applied to the finite element femur model. Axial strain, density, damage, and remodeling activity were quantified at regions predicted to be at high risk of stress fracture. The major results of this analysis predicted that marathon training increased bone damage at all regions of interest in both males and females, especially at the inferior neck. The model predicted that the superior neck, trochanter, and proximal diaphysis were more severely weakened in females than males after marathon training. While this model cannot directly quantify femoral stress fracture risk, it may be used to predict regions of bone weakness in male and female marathon runners. Future work may be done to improve accuracy of this model by using sex-specific femur geometry and bone remodeling parameters specific to male and female marathon runners. This model may be useful in future applications to study effectiveness of injury preventive methods, such as gait retraining, in reducing bone damage.

Rapid development and stiff competition in material related industries such as the automotive, demand very high precision in end products in very quick time. The transformation of raw material into an intricate-shaped final product involves various intermediate steps like design, material selection, manufacturing processes, etc. In all these steps, an in-depth understanding of material behavior plays an important role. The available traditional methods such as trial-and-error, especially in the case of die design, become highly inefficient in terms of time and money. This, there is a growing interest in simulation of the final product in order to predict different parameters which are important in design and manufacturing. Currently available simulation techniques are based on existing theories of plasticity or large deformation. These theories have been developed over several decades and many theoretical and practical issues have been debated over the years. Though the theories have great utility in understanding and solving some practical problems, there are ranges of applications for which no acceptable models are available. Most of these theories are either materials or process-specific with oversimplified real physical situations using assumptions and empirical relations. Development of field equations from first principles to stimulate elasto-plastic deformation is one such, still a subject of on-going discussion. Materials and composites exhibit hysteresis even at very low stresses, i.e., inelasticity is always present under all types of loading. This observation shows that the representing constitutive relation cannot treat the elastic and plastic deformations separately. The deformation is due to changes in size and shape, and studies with varying strain rates show considerable material sensitivity to the rate of deformation. Therefore, a generalized field equation is developed from first principles in the Eulerian coordinate system using material resistance to changes in size and shape, and their rates. The formulation uses a unified approach representing continuous effect of elastic and plastic strains and strain rates. The field equation involves eight material parameters, viz. bulk modulus, shear modulus, material shear velocity, material bulk viscosity, and four more constants associated with activation points related to deviatoric and volumetric strains and plastic strain rates. The elastic moduli, bulk and shear, are constants, and so also the material viscosities, while plastic stain rates are functions of elastic strain rates. The field equation redces to Cauchy’s equation in the solid limit and Navier-Stokes equation in the fluid limit. Simple experimental measurements are suggested to obtain the numerical values of the material parameters. Uniaxial tension tests are carried out on commercially available mild steel and aluminium alloy at different strain rates to quantify any variations in the values of material parameters during large deformation. Experimental results and the classical understanding of material deformation reveal the constant nature of elastic moduli during large deformation and, from fluids, the viscosities seem to remain constant. Around the yield region, materials experience a sharp increase in absorbed energy which is modeled to represent the plastic strain rates. The variations and contributions from elastic and plastic strains, both volumetric and deviatoric, and the corresponding stresses are observed. The effects of strain rate on plastic stress and energy absorbed are investigated. The model is checked for different materials and loading conditions to ascertain the proposed changes to earlier theories. Available experimental data in the literature are used for this purpose. The analysis shows that, though the overall stress-strain relations of different materials look similar, their internal responses differ. The internal response of a material depends on various microstructural factors, like alloying elements, impurities, etc. The present model is able to capture those internal differences between various materials. Numerical solution of different plasticity problems have to be undertaken to ascertain the applicability, generality, realism, accuracy and feasibility of the model.

The presence of residual stresses in engineering components may significantly affect damage evolution and progression towards failure. Correct evaluation of residual stress is of crucial importance for assessing mechanical components, predicting response and ensuring reliability. For example, when failure occurs due to cyclic loading, the underlying damage begins at the nano-, and then micro-scale. It is clear that improving engineering reliability at the micro-scale requires the ability to evaluate residual stress and mechanical properties at the appropriate scale. The key objective of the thesis is to advance the understanding and practice of residual stress evaluation at the micro-scale, and to examine the implications and applications that follow. Significant effort was devoted to the evaluation of two aspects of the relatively novel FIB-DIC micro-ring-core experimental technique: assessing the effects of Ga-ion damage and the quantification of uncertainty in stress evaluation due to unknown crystal orientation. FIB-DIC micro-ring-core milling was then used alongside with synchrotron XRD to study residual stress effects on fatigue crack growth propagation rate following the occurrence of overload or underload. The effects of the two principal mechanisms of crack retardation following an overload, residual stress and crack closure, were separated by testing samples at different loading ratios. Whilst, the acceleration after an underload was studied using validated non-linear FEM analyses. Conceptual focus was placed on the macro-micro-nano residual stress decomposition into Type I, II & III according to scale and, detailed examination was conducted experimentally and numerically. In the context of shot-peening surface treatment, residual stresses were modelled using a novel eigenstrain-based modelling procedure for arbitrarily shaped components. Furthermore, a fine scale characterisation was performed of the recast layer produced by EDM, with particular attention paid to the residual stress. The investigations presented in this thesis open new perspectives for the assessment of material reliability. Improved failure prediction models will be elaborated based on the insights obtained in the present study.

Introdução: A associação da fadiga muscular com o aumento da força vertical de reação do solo representa risco para a fratura por estresse de tíbia em esportes como a corrida de longa distância e o triatlo. Objetivos: analisar e comparar parâmetros do componente vertical das forças de reação do solo e parâmetros musculares isocinéticos da flexão-plantar (FP) e dorsiflexão (DF) do tornozelo entre corredores de longa distância, triatletas e indivíduos não-atletas. Materiais e Métodos: foram avaliados 75 indivíduos do sexo masculino, divididos em: Grupo Triatleta (GT) (n=26), Grupo Corredores de Longa Distância (GCL) (n=26) e Grupo Controle de não- atletas (GC) (n=23). Para avaliação da força vertical foi utilizada uma plataforma de força, onde os indivíduos realizaram passos de corrida em uma distância pré-determinada. Foram coletados dez passos (cinco com o membro direito e cinco com o esquerdo). A avaliação isocinética foi realizada no modo concêntrico/excêntrico e excêntrico/concêntrico da flexão-plantar (FP) e dorsiflexão (DF) do tornozelo direito e esquerdo. Foram feitas cinco repetições na velocidade de 60º/s e 30 repetições a 180º/s, com repouso de 10 segundos entre as séries. Resultados: O GC e o GT apresentaram forças verticais menores e maior tempo de contato com o solo e de aplicação da força na aceleração vertical máxima que o GCL. O tempo de aplicação de força foi maior no GC que o GT. A avaliação isocinética (180º/s) mostrou: maiores valores da DF excêntrica e FP concêntrica no GC e GT quando comparados com o GCL; maiores valores para DF concêntrica no GC comparado do GT e GCL e GT maior GCL; TA foi maior na DF excêntrica do GCL que GC; a maior relação agonista-antagonista FP e DF foi no modo concêntrico-excêntrico do GC quando comparado com GT e GCL. Na avaliação a 60º/s, maior PT durante a FP excêntrica e DF concêntrica no GC que GT e GCL e maior FP concêntrica no GT e GC. Conclusões: Os atletas mostraram menor força e resistência isocinéticas e maiores valores de impacto que os controles. Os triatletas tiveram menor impacto e melhor desempenho na variável de resistência muscular. / Introduction: The association of fatigue with increasing vertical force of ground reaction represent a risk for Tibial stress fracture in sports like long distance running and triathlon. Objectives: To analyze and compare the parameters of the vertical component of ground reaction forces and the parameters of muscle isokinetic ankle flexion-plantar (PF) and dorsiflexion (DF) among long distance runners, triathletes and non-athletes. Materials and Methods: total of 75 males, divided into three groups: Triathletes (GT) (n=26), Long Distance Runners (GR) (n=23) and nonathletes Controls (GC) (n=26) participated in the study. The force platform were used to record vertical forces and the subjects were instructed to perform race steps for a predetermined distance and to complete ten practical experience (five with the right limb and five with the left), which consisted of consistent landing from one of his feet in the center of the platform. The isokinetic evaluation was performed in the concentric/eccentric and eccentric/concentric ankle plantar-flexion (PF) and dorsiflexion (DF) (60°/s and 180°/s). Results:The GC and GT showed lower vertical forces, increased total time ground support and time of application of force at maximum vertical acceleration than GR. In this last variable, the GC had a time of application of force even greater than GT. To isokinetic evaluation at 180 ° / s, GT and GC presented TW significantly higher than GR, during DF eccentric and PF concentric; in DF concentric, the GC was higher than GR and GT and GT higher than GR; GR presented TA significantly higher than GT and GC, during DF eccentric; GC presented agonist-antagonist ratio for PF and DF in the concentriceccentric mode, higher than GT and GCL. For evaluation at 60 °/s, the GC presented s PT significantly higher than GT and GR, during PF eccentric and DF concentric; FP concentric GC higher than GT. Conclusions: The athletes presented lower isokinetics strength and endurance and higher impact values than the controls. The triathletes had less impact and better performance in variable muscular endurance.

Introdução: A associação da fadiga muscular com o aumento da força vertical de reação do solo representa risco para a fratura por estresse de tíbia em esportes como a corrida de longa distância e o triatlo. Objetivos: analisar e comparar parâmetros do componente vertical das forças de reação do solo e parâmetros musculares isocinéticos da flexão-plantar (FP) e dorsiflexão (DF) do tornozelo entre corredores de longa distância, triatletas e indivíduos não-atletas. Materiais e Métodos: foram avaliados 75 indivíduos do sexo masculino, divididos em: Grupo Triatleta (GT) (n=26), Grupo Corredores de Longa Distância (GCL) (n=26) e Grupo Controle de não- atletas (GC) (n=23). Para avaliação da força vertical foi utilizada uma plataforma de força, onde os indivíduos realizaram passos de corrida em uma distância pré-determinada. Foram coletados dez passos (cinco com o membro direito e cinco com o esquerdo). A avaliação isocinética foi realizada no modo concêntrico/excêntrico e excêntrico/concêntrico da flexão-plantar (FP) e dorsiflexão (DF) do tornozelo direito e esquerdo. Foram feitas cinco repetições na velocidade de 60º/s e 30 repetições a 180º/s, com repouso de 10 segundos entre as séries. Resultados: O GC e o GT apresentaram forças verticais menores e maior tempo de contato com o solo e de aplicação da força na aceleração vertical máxima que o GCL. O tempo de aplicação de força foi maior no GC que o GT. A avaliação isocinética (180º/s) mostrou: maiores valores da DF excêntrica e FP concêntrica no GC e GT quando comparados com o GCL; maiores valores para DF concêntrica no GC comparado do GT e GCL e GT maior GCL; TA foi maior na DF excêntrica do GCL que GC; a maior relação agonista-antagonista FP e DF foi no modo concêntrico-excêntrico do GC quando comparado com GT e GCL. Na avaliação a 60º/s, maior PT durante a FP excêntrica e DF concêntrica no GC que GT e GCL e maior FP concêntrica no GT e GC. Conclusões: Os atletas mostraram menor força e resistência isocinéticas e maiores valores de impacto que os controles. Os triatletas tiveram menor impacto e melhor desempenho na variável de resistência muscular. / Introduction: The association of fatigue with increasing vertical force of ground reaction represent a risk for Tibial stress fracture in sports like long distance running and triathlon. Objectives: To analyze and compare the parameters of the vertical component of ground reaction forces and the parameters of muscle isokinetic ankle flexion-plantar (PF) and dorsiflexion (DF) among long distance runners, triathletes and non-athletes. Materials and Methods: total of 75 males, divided into three groups: Triathletes (GT) (n=26), Long Distance Runners (GR) (n=23) and nonathletes Controls (GC) (n=26) participated in the study. The force platform were used to record vertical forces and the subjects were instructed to perform race steps for a predetermined distance and to complete ten practical experience (five with the right limb and five with the left), which consisted of consistent landing from one of his feet in the center of the platform. The isokinetic evaluation was performed in the concentric/eccentric and eccentric/concentric ankle plantar-flexion (PF) and dorsiflexion (DF) (60°/s and 180°/s). Results:The GC and GT showed lower vertical forces, increased total time ground support and time of application of force at maximum vertical acceleration than GR. In this last variable, the GC had a time of application of force even greater than GT. To isokinetic evaluation at 180 ° / s, GT and GC presented TW significantly higher than GR, during DF eccentric and PF concentric; in DF concentric, the GC was higher than GR and GT and GT higher than GR; GR presented TA significantly higher than GT and GC, during DF eccentric; GC presented agonist-antagonist ratio for PF and DF in the concentriceccentric mode, higher than GT and GCL. For evaluation at 60 °/s, the GC presented s PT significantly higher than GT and GR, during PF eccentric and DF concentric; FP concentric GC higher than GT. Conclusions: The athletes presented lower isokinetics strength and endurance and higher impact values than the controls. The triathletes had less impact and better performance in variable muscular endurance.

Disertační práce se věnuje problematice obecných koncentrátorů napětí v anisotropních prostředích. Zejména se jedná o problém trhlin končících na rozhraní dvou různých materiálů, či problém obecného více-materiálového klínu. Cílem práce je vytvořit komplexní nástroj pro posuzování obecných koncetrátorů napětí tj, popis pole napětí v jeho okolí, zahrnutí případného vlivu přemostění trhliny do výsledného pole napětí a definici lomových kritérií pro obecný koncentrátor v anisotropním prostředí. U popisu pole napětí je využit tzv. Lechnického-Strohův formalismus a technika spojitě rozložených dislokací využívající teorii komplexních potenciálů. V práci je rovněž široce uplatněn tzv. dvoustavový "psí"-integrál (pro výpočet různých součinitelů asymptotického rozvoje pro napětí), založený na Bettiho recipročním teorému v kombinaci s metodou konečných prvků. Pro formulaci lomových kritérií je použita teorie tzv. „konečné lomové mechaniky“ a teorie sdružených asymptotických rozvojů. Studován je především vztah mezi ohybem trhliny podél rozhraní a její případnou pentrací do základního materiálu. Veškeré potřebné výpočty jsou prováděny v matematických softwarech MAPLE 10.0, MATLAB 7.1 a konečnoprvkovém systému ANSYS 10.0.