La leptine circule en proportion de la masse graisseuse du corps et la transduction de son signal à travers la forme longue de son récepteur via un certain nombre de voies neurales , y compris MAPK, PI3-K ,AMPK et JAK2 - STAT3 . Il faut noter que STAT3 constitue une voie clée au récepteur de la leptine par laquelle la leptine module l'expression des gènes impliqués dans la régulation du bilan énergétique. La plupart des recherches ont porté sur la fonction du récepteur de la leptine au sein de l' hypothalamus, en particulier la fonction du récepteur de la leptine dans le noyau arqué. Toutefois, les récepteurs de la leptine sont également exprimés sur les neurones dopaminergiques de l'aire tégmentale ventrale et la leptine agit sur cette région du cerveau pour influencer la prise alimentaire, la motivation, la locomotion, l'anxiété et la transmission de la dopamine. De plus, la leptine active la STAT3 dans les dopaminergiques et GABAergiques populations neuronales. Bien que ces résultats contribuent à notre compréhension des multiples actions de la leptine dans le système nerveux central, il reste à résoudre les cellules et la signalisation du récepteur de la leptine qui sont responsables des effets neurocomportementaux de la leptine dans le mésencéphale. Visant à déterminer la contribution de la voie de signalisation STAT3 dans les neurones dopaminergiques du mésencéphale, nous avons généré une lignée de souris knockout conditionnel dans lequel l'activation du gène de STAT3 sur son résidu tyrosine 705 ( Tyr 705 ) est absent spécifiquement dans les neurones dopaminergiques. Avec l'utilisation de ce modèle de souris génétique, nous avons évalué l'impact de l'ablation de la signalisation STAT3 dans les neurones dopaminergiques sur un certain nombre de fonctions liées à la dopamine, y compris l'alimentation, la locomotion, les comportements liés à la récompense, l'émotion et la libération de dopamine dans le noyau accumbens. Fait intéressant, nous avons observé un dimorphisme sexuel dans le phénotype des souris STAT3DAT-KO. L'activation de la voie de signalisation STAT3 dans les neurones dopaminergiques est responsable de l'action de la leptine dans la réduction de la locomotion, récompense liée à l'activité physique, et de l'augmentation de la libération et de la disponibilité de la dopamine chez les souris mâles. Cependant, il ne module pas le comportement émotionnel. D'autre part, les souris femelles STAT3DAT-KO augmentent les niveaux d'anxiété et les niveaux plasmatiques de corticostérone, sans provoquer de changements de la dépression. Cependant, la perte d'activation de STAT3 dans les neurones dopaminergiques ne module pas le comportement locomoteur chez les souris femelles. Notamment, les actions de la leptine dans le mésencéphale pour influencer le comportement alimentaire ne sont pas médiées par l'activation de STAT3 dans les neurones dopaminergiques, considérant que les souris mâles et femelles ont un comportement alimentaire normal. Nos résultats démontrent que la voie de signalisation STAT3 dans les neurones dopaminergiques est responsable des effets anxiolytiques de la leptine, et soutient l'hypothèse que la leptine communique l'état d'énergie du corps (i.e. la relation entre la dépense et les apports énergétiques) pour les régions mésolimbiques pour atténuer les effets de motivation et de récompense de plusieurs comportements qui servent à réhabiliter ou à épuiser les réserves d'énergie. En outre, ce travail souligne l'importance d'étudier la modulation de la signalisation de la leptine dans différente types de cellules, afin d'identifier les voies de signalisation et les mécanismes cellulaires impliqués dans les différentes fonctions neuro-comportementales de la leptine. / The adipocyte-derived hormone leptin circulates in proportion to the body fat content and transduces its signal through the long form of its receptor via a number of neural pathways, including MAPK, PI3-K, AMPK and JAK2-STAT3. Of note, STAT3 constitutes a key pathway downstream to the leptin receptor by which leptin modulates the expression of genes involved in energy balance. Most research has focused on leptin receptor function within the hypothalamus, in particular leptin receptor function within the arcuate nucleus. However, leptin receptors are also expressed on dopaminergic neurons of the ventral tegmental area, and leptin has been shown to target this brain region to influence feeding, motivation, locomotion, anxiety and dopamine tone. Moreover, leptin activates STAT3 in both dopaminergic and GABAergic neuronal populations. Although these findings contribute to our understanding of the multiple actions of leptin in the central nervous system, it remains to be resolved which cells and leptin receptor signaling pathway mediates the neurobehavioral effects of leptin in the midbrain. Aiming at determining the contribution of STAT3 signaling in midbrain DA neurons, we generated a line of conditional knockout mice in which the main activation site of STAT3 gene (tyr 705) is absent specifically in dopaminergic neurons (STAT3DAT-KO mice). Using this genetic mouse model, we assessed the impact of ablation of STAT3 signaling in dopaminergic neurons on a number of dopamine-related functions, including feeding, locomotion, reward-related behaviors, emotion and nucleus accumbens dopamine release. Interestingly, we observed a sexual dimorphism in the phenotype of STAT3DAT-KO mice. STAT3 signaling in DA neurons mediates the actions of leptin in the midbrain to decrease locomotion and running reward, and to increase dopamine release and availability in male mice. However, it does not modulate emotional behavior. On the other hand, STAT3DAT-KO female mice exhibited increased anxiety-like behavior accompanied by increased plasma corticosterone levels, without changes in behavioral despair relative to littermate controls. However, loss of STAT3 activation in dopaminergic neurons does not modulate locomotor behavior in female mice. Notably, the actions of leptin in the midbrain to influence feeding behavior are not mediated by STAT3 signaling in dopaminergic neurons, as both male and female STAT3DAT-KO mice have normal feeding behavior as compared to littermate controls. Our results demonstrate that STAT3 signaling in dopaminergic neurons mediates the anxiolytic actions of leptin, and support the hypothesis that leptin communicates body energy status (defined as a relationship between energy intake and energy expenditure) to mesolimbic regions to adjust the motivational and rewarding effects of multiple behaviors that serve to either restore or deplete energy stores. In addition, this work highlight the importance of studying cell-type specific modulation of leptin signaling molecules to tease apart pathways and the mechanisms involved in the different neurobehavioral functions of this adipocyte-derived hormone.

This thesis is concerned with mathematical modelling and optimal control of constrained systems. Each of the systems under consideration is a system that can be controlled by one of the variables, and this control is subject to constraints. First, we consider middle-distance running where a runner's horizontal propulsive force is the control which is constrained to be within a given range. Middle-distance running is typically a strategy-intensive race as slipstreaming effects come into play since speeds are still relatively fast and runners can leave their starting lane. We formulate a two-runner coupled model and determine optimal strategies using optimal control theory. Second, we consider two applications of control systems with delay related to R&D expenditure. The first of these applications relates to the defence industry. The second relates to the pharmaceutical industry. Both applications are characterised by a long delay between initial investment in R&D and seeing the benefits of R&D realised. We formulate models tailored to each application and use optimal control theory to determine the optimal proportion of available funds to invest in R&D over a given time horizon. Third, we consider a mathematical model of urban burglary based on the Short model. We make some modifications to this model including the addition of deterrence due to police officer presence. Police officer density is the control variable, which is constrained due to a finite number of police officers. We look at different control strategies for the police and their effect on burglary hot-spot formation.

La course d’endurance active le système de récompense (SR) et est reliée aux comportements de recherche alimentaire. L’influence de la leptine sur l’activité physique (AP) volontaire est bien documentée d’un point de vue physiologique, mais très peu en termes d’impact hédonique. La leptine inhibe l’effet récompensant lié à la consommation de nourriture et joue un rôle semblable pour d’autres types de stimuli. La leptine s’arrime à la forme longue du récepteur à la leptine (Leprb) situé sur les neurones à dopamine (DA) et GABA de l’aire tegmentale ventrale (ATV) dans le mésencéphale. Signal transducer and Activator of Transcription 3 (STAT3) est un facteur de transcription important de la cascade de signalisation de la leptine. La phosphorylation de STAT3 n’est détectée que dans une parcelle des neurones DA positifs pour le Leprb, conférant aux neurones DA STAT3-spécifiques des caractéristiques uniques. Nous avons généré un modèle murin invalidé pour STAT3 sélectivement dans les neurones DA (STAT3DAT-KO). La première expérience consistait à évaluer les paramètres métaboliques de base de notre modèle en utilisant les chambres métaboliques Comprehensive Lab Animal Monitoring System (CLAMS), incluant l’activité ambulatoire, le ratio d’échanges respiratoires (RER) et la production de chaleur. Les STAT3DAT-KO sont hyperactives, démontré par une activité locomotrice augmentée, mais aucune variation entre les deux groupes n’est observée pour le RER et la production de chaleur, en plus d’un gain de poids identique. Une stratégie de récupération ciblant la réinsertion de STAT3 dans les neurones DA du système mésolimbique normalise l’AP anciennement plus élevée des STAT3DAT-KO à celle des contrôles, suivant l’accès libre à une roue d’exercice (RE) pour une durée de 4 semaines, suivant l’accès libre à une roue d’exercice (RE) pour une durée de 4 semaines. L’injection d’un psychostimulant (agoniste du récepteur DA de type 1 (D1R), le Chloro-APB-Hydrobromide (SKF 82958)) reflète une fonction dopaminergique réduite chez les STAT3DAT-KO. Un test de recherche compulsive de nourriture révèle une suppression de la prise alimentaire chez les deux groupes expérimentaux. Nous démontrons pour la première fois que la motivation alliée à la course d’endurance, indépendamment de la régulation de la prise alimentaire par la leptine, est dépendant d’une signalisation leptine-STAT3 amoindrie dans les neurones DA du système mésolimbique, révélant STAT3 comme élément clé dans la régulation du tonus dopaminergique et des propriétés récompensantes de l’AP. / Endurance running is rewarding and related to food seeking behaviors. Influence of leptin on voluntary physical activity is well documented from a physiological point of view, but little is known about its hedonic impact. Leptin inhibits the rewarding aspects of food consumption and plays a similar role for other types of stimuli. Leptin binds to the long form of the leptin receptor, situated on dopamine (DA) and GABA neurons of the ventral tegmental area (VTA) in the midbrain. Signal Transducer and Activator of Transcription 3 (STAT3) is an important transcription factor of the leptin signalling cascade. Phosphorylation of STAT3 is detected only in a subset of neurons that are positive for the leptin receptor, conferring unique properties to DA STAT3 neurons. We generated a mouse model invalidated for STAT3 selectively in dopamine neurons (STAT3DAT-KO). We first assessed basic metabolic parameters of our model using CLAMS metabolic chambers, including ambulatory acitivity, respiratory exchange ratio (RER) and heat production. STAT3DAT-KO are hyperactive as seen by a higher locomotor activity, but there is no inter-group variation of RER and heat production, and the weight gain is the same. A rescue strategy targeting the reinsertion of STAT3 in DA neurons of the mesolimbic system normalizes physical activity of the STAT3DAT-KO - which was previously much higher - to that of the control mice, following free access to a running wheel for a period of 4 weeks. The injection of a psychostimulant (agonist of the type1 DA receptor (D1R), Chloro-APB-Hydrobromide (SKF 82958)) reflects a reduced DA signalling STAT3DAT-KO. A compulsive food seeking test reveals a suppression of sucrose intake in both experimental groups. We demonstrate for the first time that the motivation allied to endurance running, independently of food intake regulation by leptin, is dependent upon a diminished leptin-STAT3 signalling in DA neurons of the midbrain, revealing STAT3 as a key player in the regulation of DA tone and the rewarding properties of physical activity.

Theoretical part of this thesis is focused on a heart rate, especially its parameters, measurement methods and regulation. Moreover describes maximal heart rate issue. Practical part was performed as an experimental measurement of maximal heart rate level of 40 healthy adult probands (20 men and 20 women) between the ages of twenty and forty. Maximal heart rate was measured by telemetry meter FT4 Polar ® in 3 types of exercise tests - running, ergometer cycling and swimming. Results were statistically processed. Study confirmed significant differences in maximal heart rate during running, ergometer cycling and swimming. Highest heart rate was reached while running for 95% of measured volunteers and the lowest heart rate was reached during swimming for 98% of probands. The objective of this thesis was a comparison of reached heart rates during different exercise tests and highlight the evidence of dissimilar maximal heart rate during different exercises. Powered by TCPDF (www.tcpdf.org)

Title: Musculoskeletal assessment analysis of triathletes Objectives: The main aim of this master degree thesis is the diagnostics of the current condition of the complex kinesiological examination of musculo-skeletal system in elite performance triathtletes of the Czech National Team level (Junior and U23 categories), including compensational exercises specifically devised for triathlets. Futhermore with the help of the selected data this study is expected to draw some basic conclusions and establish the typical postural characteristics of athletes related to the sport of triathlon. Methods: In this thesis we have used following testing methods: complex musculo skeletal examintation including evaluation of medical history, an antropometrical screening, standing static postural assessment, gait assessment, soft-tissue palpation exam, assessment of the fundamental movement patterns of an individua, examination of neurological reflexes, flexibility and range of motion screening. Based on the above mentioned tests we have received a complete functional and musculo skeletal system profile of each triathlete's. For collection we have used the SPSS 22 data analysis software. For the gender diferentiation we have used non-pairred T-Test and for perofrmance variability within the 3 levels we have used...

In this work we model the historical development of best performances in men's 100, 200, 400 and 800m running events. We suppose that the years best performances are independent random variables with generalized extreme value distribution for minima and that there is a decreasing trend in location. Parameters of the models are estimated by using maximum likelihood techniques. The data of years best performances are missing for some years, we treat them as right censored data that are censored by value of world record valid at that time. Graphic tools used for models diagnostics are adjusted to the censoring. The models we get are used to estimate the ultimate records and to predict new records in next years. At the end of the work we estimate several models describing historical development of years best performances for more events at one time.

Title: Functional strength in running preparation of soldiers of Czech army Objectives: The main objective of this work is to create a reservoir of exercises of increasing functional strength runners. Creating a poll for functional strength between physical education employees of Czech army and civilian coaches. Methods: At work I used the method of analysis of scientific literature in the field of functional strength. Qualitative research method I used to obtain information from respondents in the form of survey forms. Results: Result of this work is the basic reservoir of thirty-two exercises that assist in increasing and improving running functional strength and which can be used in running training soldiers of Czech army. Another result of the survey is to evaluate the awareness of trainers on the concept of functional strength and definition of this concept. Keywords: Functional strength, strength, coordination and balanced skills, running training, functional, natural movements, kinetic chain.

De nombreux cas de mortalité de Sapin pectiné (Abies alba Mill.) sont constatés en limite sud de son aire de répartition en Provence et semblent être liés aux sécheresses successives de la dernière décennie et à la répartition des propriétés hydriques du sol. L’enjeu est alors de mieux évaluer l’impact du stress hydrique sur le fonctionnement écophysiologique de cette espèce et de pouvoir caractériser et cartographier les zones les plus vulnérables à la sécheresse. Sur le Mont Ventoux, une expérimentation a été mise en place pour suivre pendant 3 ans différents paramètres écophysiologiques impliqués dans le comportement hydrique du Sapin pectiné sur des placettes pour lesquelles les propriétés du sol étaient caractérisées. Sur cette montagne de type karstique, les profondeurs de sols sont très variables et, à l'échelle stationnelle, les taux de mortalité et les intensités de stress hydrique étaient plus élevés sur les sols ayant une réserve hydrique plus importante. De plus, un arrière-effet de la sécheresse de 2009 a été observé réduisant durablement la transpiration de l'année suivante. Une approche par modélisation mécaniste a alors été adoptée en intégrant de nouveaux formalismes sur la dynamique racinaire permettant de prendre en compte cet arrière-effet. Elle a été évaluée sur les différents paramètres impliqués dans le cycle de l'eau et du carbone des arbres et le modèle a été validé sur les dynamiques de transpiration et d’accroissement en largeur de cernes des troncs. Des indices basés sur la mesure de température de surface ont été utilisés pour évaluer la possibilité de détecter le stress hydrique en forêt. Il existe une variabilité résiduelle liée aux facteurs climatiques et à la dimension réduite de la surface de mesure dans la relation entre transpiration et température de surface à l'échelle de l'arbre. A l’échelle du versant, la température de surface a permis d'identifier la répartition spatiale de la durée et de l'intensité du stress hydrique en accord avec la typologie de sol réalisées. La télédétection dans l'infrarouge thermique pourrait ainsi être un outil intéressant pour la gestion forestière. / Many reports of deaths of silver fir (Abies alba Mill.) are mentioned at the southern limit of its limit of distribution in Provence and appear to be related to the successive droughts of the last decade and to the distribution of soil water properties. The aim of the study is then to better assess the impact of water stress on ecophysiological functioning of this species and to characterize and map the areas more vulnerable to drought. On the Mont Ventoux, an experiment was set up to monitor for 3 years ecophysiological parameters involved in the water behaviour of silver fir on plots where soil properties were characterized. On this type of karstic mountain, soils depth is highly variable and, at forest stand scale, mortality rates and intensities of water stress were higher on soils with greater water reserve. In addition, a post-effect of the drought of 2009 was observed by reducing transpiration of the following year. A mechanistic modelling approach was then adopted by integrating new formalisms of root dynamics to take into account this post-effect. It was evaluated on various parameters involved in the water and carbon cycles of trees and the model was validated on the dynamics of transpiration and on annual rings width increment of tree trunks.Indices based on measured surface temperature were used to assess the possibility of detecting water stress in forests. At tree scale, there is a residual variability due to climatic factors and to the small size of the measurement surface in the relationship between transpiration and surface temperature. At the mountainside scale, surface temperature indices allowed identifying the spatial distribution of the duration and intensity of water stress according to the typology of soil done. Remote sensing in the thermal infrared could then be a useful tool for forest management.

L’objectif de ce travail de thèse a été d’analyser les stratégies de réduction de la fatigue musculaire en course de trail et potentiellement d’identifier certains paramètres d’influence de cette fatigue. La course de trail est un nouveau sport en essor qui induit une combinaison spécifique de fatigue et dommages musculaires des principaux muscles locomoteurs. Afin de pouvoir conduire des études interventionnelles, une étude descriptive préliminaire a été conduite pour caractériser la fatigue spécifique et les dommages musculaires induits par ce type d’épreuve de trail. Ensuite, la reproductibilité du trail comme modèle de fatigue a été vérifiée afin de pouvoir l’utiliser dans un contexte d’intervention. Enfin, deux études visant à réduire la fatigue induite par le trail ont été conduites. D’une part l’utilisation des vêtements de compression - très à la mode en trail a été analysée comme stratégie d’optimisation de la performance. D’autre part, a aussi été étudié l’effet d’un réchauffement préalable du muscle sur les dommages musculaires : Dans cette optique, une étude contrôlée en laboratoire a été menée, examinant les effets d’un réchauffement passif sur les conséquences fonctionnelles de course en descente chez une population non-entraînée. En résumé, les travaux conduits au sein de cette thèse fournissent une description de la fatigue en trail, et valident l’utilisation du trail comme modèle reproductible de terrain pour investiguer les stratégies de réduction de la fatigue. De plus, ils relativisent l’effet positif des vêtements de compression sur la performance et montrent le lien fonctionnel entre le réchauffement musculaire et la réduction des dommages musculaires induits par un travail excentrique. / The aim of this thesis was to analyse strategies to reduce muscular fatigue in trail running and potentially draw conclusions on the underlying mechanisms. Trail running is a new and upcoming sport that induces a combination of fatigue and muscle damage in the main locomotor muscles. To obtain conclusive evidence on the effect of intervention studies a preliminary descriptive study was undertaken to characterise typical fatigue and damage. Subsequently a model was developed and validated that would allow the investigation of interventions in an applied field setting. A popular current strategy in trail running is the use of compression garments; therefore the effect of these on performance was studied as an intervention. Furthermore, prior heating is anecdotally considered beneficial and recent research has suggested a potential mechanism to link this with reduced muscle damage. Therefore a controlled laboratory study was conducted, examining the effects of passive heating on functional consequences of downhill running in an untrained population. In synopsis, the research conducted for this thesis provides descriptive evidence and a validated terrain model to further investigate fatigue reduction strategies in trail running. Additionally it adds to the current literature in disproving a positive effect of compression garments on performance and demonstrating the functional link between heating and eccentric-induced muscle damage reduction.

The main motivation of this doctoral thesis is to extend the current knowledge about the tribological behavior of a precipitation-hardenable (PH) austenitic stainless steel (SAE XEV-F or DIN 1.4882), used for manufacturing exhaust valves for internal combustion engines in passenger cars. For this purpose, dry sliding laboratory tests were carried out using this steel and other steels, mainly austenitic and martensitic, used as model materials for the comparative characterization of wear and friction. Experimental tests were conducted using an SRV®4 tribometer in a ball-on-disc configuration with reciprocating movement, in which the discs were the samples and the balls the counter-bodies. Four kinds of steels were tested: a) AISI 310, b) SAE XEV-F, c) AISI H13, and d) Nitrided SAE XEV-F. The ball was made of AISI 52100 bearing steel. The tests were conducted at room temperature and fixed conditions of time (sliding distance) (up to 73.2 m), load (100 N), frequency (10 Hz) and stroke (2mm). Wear was evaluated by means of mass loss in the disc and the ball, and post examination of the worn surfaces. Post examination was conducted using scanning electron microscopy (SEM), coherence correlation interferometry (CCI), and X-Ray diffraction (XRD). Wear debris resulting from tribological interaction were also investigated using SEM and XRD. Additionally, the friction coefficient was measured. High speed filming and interrupted tests were also performed at specific sliding distances. This work reports a severe-to-mild wear transition occurring during the first stage of tribological interaction (running-in) and its relation to the load distribution variation at the interface throughout the tribological tests. The wear transition was observed in different steel-on-steel tribosystems in ball-on-disc contact configuration and occurred due to the combined effects of two factors: a) the contact pressure reduction, due to the increase of nominal contact area caused by wear; and b) subsurface strain hardening (when relevant). The pressure/distance variation was determined experimentally and modeled empirically. Subsurface strain hardening was observable (and measurable) mainly the austenitic steels. Significant differences in wear (and friction) were observed between homogeneous (monophasic) steels and the heterogeneous (multiphasic) SAE XEV-F valve steel. Wear in the homogeneous steels presented an inverse correlation with hardness. Wear on the AISI 310 presented non-linear wear rates for a significant portion of the test. Wear on the SAE XEV-F valve steel was pronounced (even in the mild regime) due to a combined effect of two factors: a) formation of hard debris, which induced an abrasive component to wear by relative sliding, and b) subsurface NbC fracture, which markedly affected the material removal due to plastic deformation in the surrounding matrix. Wear of the nitrided SAE XEV-F steel was lower than that of the non-nitrided samples by nearly two orders of magnitude. The benefits of nitriding in the SAE XEV-F were two-fold: a) an increased surface hardness, and b) the prevention of NbC fracture and detachment, which results in even higher wear resistance. / A principal motivação desta tese é ampliar o conhecimento atual sobre o comportamento tribológico de um aço inoxidável austenítico endurecível por precipitação (PH), o SAE XEV-F (ou DIN 1.4882), utilizado para a fabricação de válvulas de exaustão de motores de combustão interna para carros de passageiros. Para este propósito, foram realizados ensaios laboratoriais de deslizamento a seco usando este aço e outros, principalmente aços austeníticos e martensíticos, usados como materiais modelo para a caracterização comparativa do desgaste e do atrito. Os ensaios experimentais foram conduzidos usando um tribômetro SRV®4 em uma configuração esfera-disco com movimento alternado, em que os discos foram as amostras e as esferas são os contracorpos. Foram ensaiados quatro tipos de aços: a) AISI 310, b) SAE XEV-F, c) AISI H13, e d) SAE XEV-F nitretado. A esfera era feita de aço para rolamento AISI 52100. Os ensaios foram realizados a temperatura ambiente e usando condições fixas de tempo (distância total percorrida até 73.2 m), carga normal (100 N), frequência (10 Hz) e amplitude da oscilação (2 mm). O desgaste foi avaliado por meio de perda de massa, tanto do disco quanto da esfera, e exame das superfícies desgastadas utilizando microscopia eletrônica de varredura (MEV), interferometria de correlação de coerência (ICC) e difração de raios-X (DRX). Os debris de desgaste resultantes da interação tribológica também foram investigados usando MEV e DRX. Adicionalmente, a evolução do coeficiente de atrito foi analisada. Também foram realizadas filmagens de alta velocidade e ensaios interrompidos em tempos de deslizamento específicos. Este trabalho reporta uma transição de desgaste severo para moderado que ocorre durante as a primeira fase da interação tribológica (running-in) e sua relação com a variação da carga na interface durante os ensaios tribológicos. A transição de desgaste foi observada em diferentes tribo-sistemas de aço-contra-aço na configuração esfera-plano e ocorreu principalmente por efeitos combinados de dois fatores: a) a redução da pressão de contato, devida ao aumento da área nominal causada pelo desgaste; e b) o encruamento subsuperficial (quando relevante). A variação pressão/distância foi determinada experimentalmente e modelada empiricamente. Encruamento por deformação subsuperficial foi observável (e medível) principalmente nos aços austeníticos. Foram observadas diferenças significativas no desgaste (e atrito) entre os aços homogêneos (monofásicos) e o aço de válvula SAE XEV-F, heterogêneo (multifásico). O desgaste nos aços homogêneos apresentou uma correlação inversa com a dureza. O desgaste no aço válvula SAE XEV-F foi pronunciado (mesmo no regime de desgaste moderado) devido a um efeito combinado de dois fatores: a) a formação de debris duros, o que induziu uma componente abrasiva ao desgaste por deslizamento relativo, e b) a fratura subsuperficial do NbC, o que afetou significativamente a remoção de material devida à deformação plástica da matriz. O desgaste do aço nitretado SAE XEV-F foi menor que o das amostras não tratadas em quase duas ordens de grandeza. Os benefícios da nitretação no aço válvula SAE XEV-F foram dois: a) o aumento da dureza da superfície, e b) a prevenção da fratura e desprendimento de NbC, o que resulta em uma resistência de desgaste ainda maior.