Few studies have compared balance between aging black (BW) and white women (WW) and examined its relationship to muscle mass and bone mineral density (BMD). Nineteen BW and 56 WW between 60-91 years participated. Upper and lower body strength, body composition, BMD, volitional and non-volitional control of dynamic balance, and physical activity ratings were assessed. There were no differences in strength between the groups. A trend was reported for total body BMD (p=0.07). WW exhibited better control of rapid volitional movements, in the limits of stability and rhythmic weight shift tests. The relationships of strength and muscle mass to BMD and balance were weak. Physical activity ratings were higher for WW than BW (p<.05). In conclusion, differences reported in the literature between BW and WW for risk of falling may be due to other variables not assessed in this study. Future studies should examine other factors that contribute to increased risk of falling.

Orientador: Roberto Carlos Burini / Banca: Sebastião Gobbi / Banca: Fábio Leira Orsatti / Resumo: A redução da força muscular pode ser responsável pela menor mobilidade e capacidade funcional, maior dependência e em muitos casos, maior mortalidade. O objetivo do estudo foi discriminar os desvios de composição muscular esquelética e adiposa corporal mediante exercícios de força específicos para segmentos corporais de adultos. Foram avaliados em estudo transversal 460 indivíduos de ambos os sexos, com 40 anos ou mais, participantes voluntários do programa de mudança de estilo de vida "Mexa-se Pró-Saúde". Foram mensurados massa corporal e estatura para posterior cálculo do índice de massa corporal (IMC), circunferência abdominal (CA), massa muscular (MM), força muscular pelo teste de uma repetição máxima (1-RM), em diferentes exercícios e a força de preensão manual (PM). Os dados foram expressos em média e desvio padrão. A análise de variância (ANOVA) foi utilizada para verificar as diferenças entre os grupos, seguida do teste de Tukey. Foi feita distribuição percentilar para massa muscular e circunferência abdominal para obtenção dos quatro grupos antropométricos (Hipotróficos, Hipertróficos, Obesos Hipotróficos e Obesos Hipertróficos). Para as associações entre força muscular e os grupos, foi feito o teste de qui-quadrado, seguido de modelo de regressão logística para predição das razões de chance. Os grupos definidos pela maior ou menor massa muscular corporal e adiposa abdominal podem ser discriminados pelos exercícios de força apenas quando presente o déficit muscular, na ausência de hiperadiposidade. Foram sensíveis para essas discriminações os exercícios de membros superiores, e, individualmente, todos os exercícios realizados nas mulheres e, apenas três nos homens. O maior poder protetor para não pertencer ao grupo hipotrófico, foi a força muscular aumentada (P75) na extensão de cotovelo (OR 0,75), da flexão... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Muscle strength reduction may be responsible for impaired mobility and functional capacity, greater dependence and, in many cases, higher mortality. This study aimed at discriminating deviances in skeletal and adipose muscle composition by means of specific strength exercises for adults' body segments. Four hundred and sixty individuals, males and females aged 40 years or older were evaluated. They were voluntary participants in the lifestyle change program "Mexa-se Pró-Saúde". Body mass and stature were measured for later estimation of the body mass index (BMI), waist circumference (WC), muscle mass (MM), muscle strength by the one repetition maximum test (1-RM) in various exercises and hand grip (HG) strength. Data were expressed by means and standard deviations. The analysis of variance (ANOVA) was used to evaluate differences between groups, and it was followed by Tukey's test. Percentile distribution was performed for muscle mass and abdominal circumference in order to form the four anthropometric groups (Hypotrophy, Hypertrophic, Obese hypotrophy and Obese hypertrophy). The chi-square test was used for associations between muscle strength and the groups, which was followed by a logistic regression model for predicting the odds ratios. The groups defined by higher or lower body muscle mass and abdominal adipose mass can be discriminate by strength exercises only when muscular deficit is present, in the absence of hyperadiposity. The exercises for upper limbs and, individually, all the exercises performed in women and only three in men were sensitive for such discrimination. The greatest protective power for not belonging to the hypotrophic group was increased muscle power (P75) at elbow extension (OR 0.75), elbow flexion (OR 0.85) and HG (OR 0.85). Inversely, these indicators constituted a risk factor for belonging to the hypertrophic obese group for higher muscle... (Complete abstract click electronic access below) / Mestre

Made available in DSpace on 2014-06-11T19:29:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-25Bitstream added on 2014-06-13T18:59:07Z : No. of bitstreams: 1 dalanesi_rc_me_botfm.pdf: 278375 bytes, checksum: 056b03e1f7372583c352b61f3b53720d (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A redução da força muscular pode ser responsável pela menor mobilidade e capacidade funcional, maior dependência e em muitos casos, maior mortalidade. O objetivo do estudo foi discriminar os desvios de composição muscular esquelética e adiposa corporal mediante exercícios de força específicos para segmentos corporais de adultos. Foram avaliados em estudo transversal 460 indivíduos de ambos os sexos, com 40 anos ou mais, participantes voluntários do programa de mudança de estilo de vida “Mexa-se Pró-Saúde”. Foram mensurados massa corporal e estatura para posterior cálculo do índice de massa corporal (IMC), circunferência abdominal (CA), massa muscular (MM), força muscular pelo teste de uma repetição máxima (1-RM), em diferentes exercícios e a força de preensão manual (PM). Os dados foram expressos em média e desvio padrão. A análise de variância (ANOVA) foi utilizada para verificar as diferenças entre os grupos, seguida do teste de Tukey. Foi feita distribuição percentilar para massa muscular e circunferência abdominal para obtenção dos quatro grupos antropométricos (Hipotróficos, Hipertróficos, Obesos Hipotróficos e Obesos Hipertróficos). Para as associações entre força muscular e os grupos, foi feito o teste de qui-quadrado, seguido de modelo de regressão logística para predição das razões de chance. Os grupos definidos pela maior ou menor massa muscular corporal e adiposa abdominal podem ser discriminados pelos exercícios de força apenas quando presente o déficit muscular, na ausência de hiperadiposidade. Foram sensíveis para essas discriminações os exercícios de membros superiores, e, individualmente, todos os exercícios realizados nas mulheres e, apenas três nos homens. O maior poder protetor para não pertencer ao grupo hipotrófico, foi a força muscular aumentada (P75) na extensão de cotovelo (OR 0,75), da flexão... / Muscle strength reduction may be responsible for impaired mobility and functional capacity, greater dependence and, in many cases, higher mortality. This study aimed at discriminating deviances in skeletal and adipose muscle composition by means of specific strength exercises for adults’ body segments. Four hundred and sixty individuals, males and females aged 40 years or older were evaluated. They were voluntary participants in the lifestyle change program “Mexa-se Pró-Saúde”. Body mass and stature were measured for later estimation of the body mass index (BMI), waist circumference (WC), muscle mass (MM), muscle strength by the one repetition maximum test (1-RM) in various exercises and hand grip (HG) strength. Data were expressed by means and standard deviations. The analysis of variance (ANOVA) was used to evaluate differences between groups, and it was followed by Tukey’s test. Percentile distribution was performed for muscle mass and abdominal circumference in order to form the four anthropometric groups (Hypotrophy, Hypertrophic, Obese hypotrophy and Obese hypertrophy). The chi-square test was used for associations between muscle strength and the groups, which was followed by a logistic regression model for predicting the odds ratios. The groups defined by higher or lower body muscle mass and abdominal adipose mass can be discriminate by strength exercises only when muscular deficit is present, in the absence of hyperadiposity. The exercises for upper limbs and, individually, all the exercises performed in women and only three in men were sensitive for such discrimination. The greatest protective power for not belonging to the hypotrophic group was increased muscle power (P75) at elbow extension (OR 0.75), elbow flexion (OR 0.85) and HG (OR 0.85). Inversely, these indicators constituted a risk factor for belonging to the hypertrophic obese group for higher muscle... (Complete abstract click electronic access below)

京都大学 / 0048 / 新制・課程博士 / 博士(社会健康医学) / 甲第22153号 / 社医博第101号 / 新制||社医||10(附属図書館) / 京都大学大学院医学研究科社会健康医学系専攻 / (主査)教授 中山 健夫, 教授 小川 修, 教授 川村 孝 / 学位規則第4条第1項該当 / Doctor of Public Health / Kyoto University / DFAM

This study extends the Theory of Planned Behavior by drawing on research investigating the 'halo effect,' which posits that physically attractive people are more likely to be hired, get a raise, perceived positively, and/or live happily within certain professions. Extant work has shown this trend is not generalizable across all fields. For example, scientists who are viewed as relatively unattractive and unsociable are perceived as producing higher quality research compared to their more attractive and sociable counterparts. The fitness industry, and the bodybuilding community in particular, presents an interesting issue where muscularity is an indicator of expertise and credibility, however, for female bodybuilders a muscular physique may diminish her perceived attractiveness and diminish such evaluations. Drawing on the Theory of Planned Behavior, this study examines how muscularity influences assessments of attractiveness, credibility, and homophily and indirectly influences participants' attitudes and perceived control over theory own weight lifting behavior. Though the hypothesized model was not a good fit, an exploratory respecification of the proposed model shows physical attractiveness plays a central role in assessments of homophily, credibility, and attitude. / Master of Arts

Background.Studies have shown that low-grade chronic inflammation affect muscle mass negatively. Theimpact of inflammation in grip strength is not yet investigated. Existing studies are made on a few populations.This study aims to describe how inflammation, grip strength and muscle mass looks in agroup of 52-year-old men and women and to examine the differences between the sexes.Another aim is to investigate the correlations between low-grade chronic inflammation (n =32) and muscle mass (n = 23) and grip strength (n = 30).Method Data from an ongoing study were analyzed with a non-experimental descriptive, comparativeand correlating design. Lean muscle mass was calculated by subtracting the percentage of fatfrom weight. Grip strength was measured by Jamar dynamometer. CRP as inflammationparameter through blood-samples. Results The populations measured levels was consistent with current reference values för healthyindividuals. Tendencies to positive correlation between CRP and muscle mass could be seenfor both men and women. For men there were tendency towards positive correlation betweenCRP levels and grip strength, while tendency to negative correlation for women. Women hadhigher CRP levels compared to men. Men had higher levels of muscle mass and grip strength. Conclusion No conclusions could be drawn regarding the effect of low-grade chronic inflammation effectin fat-free mass and grip strength. The study has highlighted the need for further research inthe field.

Background: In 2014, there were nearly 2 billon overweight people around the world. This causes excessive costs for the society and is also a threat to the human condition. In recent time, there has been an increase of understanding the individual parts of the body composition. One method to measure body composition is using a bioelectrical impedance analyzer. The current recommendation is to measure during fasting conditions. However, there are few studies that have investigated a meal’s effect on body composition measured with bioelectrical impedance analysis, and those studies have presented varying results. If a bioelectrical impedance analyzer could be used without previous fasting, it would increase the use and utility of bioelectrical impedance analyzers. This could in turn, for example, reduce waiting lists in hospitals where bioelectrical impedance analyzers are used. Aim: The main aim of this study was to investigate a meal’s effect on body composition when measured with a bioelectrical impedance analyzer. The secondary aim was to investigate the correlation between skeletal muscle mass and hand grip strength when using a bioelectrical impedance analysis and a hand-held dynamometer respectively, during fasting conditions. Methods: In this present study, 27 subjects in the age of 21-59 years old participated. The subjects arrived at the laboratory in the morning during fasting conditions. Firstly, a bioelectrical impedance analyze and a hand grip strength test were completed. Thereafter, all subjects ate a meal containing at least 500 kcal. The following bioelectrical impedance analysis were completed 60, 90 and 120 minutes’ post meal intake. The data was then analyzed in SPSS version 20 through a paired T-test and a Pearson correlation test respectively. Results: The results showed that all body composition parameters investigated in this present study, except for minerals, not were statistically different 90 minutes after a meal intake containing at least 500 kcal, compared to the fasting condition, when measured with a bioelectrical impedance analyzer. Furthermore, a moderate correlation was found between hand grip strength and skeletal muscle mass for women. The same correlation was found weak for men. Conclusion: The results from this present study indicates that it is possible to measure body composition with a bioelectrical impedance analyzer 90 minutes’ post meal intake, except for minerals. Also, it indicates that a hand grip strength test is not a valid test for measuring skeletal muscle mass.

O presente estudo investigou o efeito de diferentes intensidades do treinamento de força (TF), aplicadas com volume total de treino (VTT) equalizado, nos ganhos de força dinâmica máxima (1RM) e massa muscular dos membros superiores e inferiores. Trinta voluntários do sexo masculino, com idade entre 18 e 30 anos, participaram de 12 semanas de TF com uma frequência semanal de duas sessões. Foi utilizado um protocolo de treinamento unilateral com um dos lados do corpo realizando o exercício com intensidade equivalente a 20% 1RM (G20) e o lado contralateral utilizando uma das três intensidades 40%, 60% ou 80% 1RM (G40, G60 e G80, respectivamente). O grupo G20 realizava três séries compostas de repetições até a falha concêntrica e o VTT era calculado e replicado para os demais grupos. A força dinâmica máxima e a área de secção transversa (AST) dos músculos flexores do cotovelo e do vasto lateral foram avaliadas nos momentos pré, 6 semanas e pós-treinamento. Os resultados demonstraram que os grupos G40, G60 e G80 apresentaram ganhos similares de AST (25%, 25,1% e 25%, flexores do cotovelo e 20,5%, 20,4% e 19,5% vasto lateral, respectivamente, p<0,05). Somente o grupo G80 demonstrou diferença significante com o grupo G20 na comparação do período pós-treinamento (25% e 14,4%, respectivamente para os flexores do cotovelo e 19,5% e 7,9%, respectivamente para vasto lateral, p<0,05). Para os ganhos de 1RM o grupo G80 demonstrou maiores aumentos após 12 semanas de TF para a flexão unilateral do cotovelo na posição em pé (54,2% p<0,05) e para o leg press 45º os grupos G60 e G80 demonstraram os maiores aumentos (55,4% e 45,7%, respectivamente, p<0,05). Assim, quando o VTT foi equalizado entre diferentes intensidades (40, 60 e 80% 1RM) os ganhos da AST tanto dos flexores do cotovelo quanto o vasto lateral foram semelhantes e a intensidade de 20% 1RM não causou aumento significante da AST. No que diz respeito a força muscular as intensidades mais elevadas (60% e 80% 1RM) foram superiores em promover ganhos de força do que as demais intensidades utilizadas. Esses dados sugerem que ao equalizar o VTT os ganhos de massa muscular são semelhantes para as intensidades de treinamento entre 40- 80% 1RM. Além disso, a intensidade de 20% 1RM, mesmo com o VTT equalizado com as intensidades maiores, não promove aumentos de massa muscular para ambos os segmentos corporais. Por outro lado, intensidades altas de treinamento produzem os maiores ganhos de força máxima em membros superiores e inferiores / The present study investigated the effect of different resistance training (RT) intensities, with equal total training volume (TTV), on maximal dynamic strength (1RM) and upper and lower limbs muscle cross sectional area (CSA). Thirty men engaged in a twice a week training period for 12 weeks. The study was carried out with a within subject design. Thus, one leg and one arm were set at 20% 1RM (G20) for all subjects and the contralateral side was randomly assigned to one of three possible groups (i.e. G40, G60 and G80, 40%, 60% and 80% 1RM, respectively). The leg and arm that were set at 20% 1RM always started the resistance training session and performed 3 sets to concentric muscle failure. TTV (sets x repetition x mass) was recorded and replicated to other groups. The maximal dynamic strength and elbow flexors and vastus lateralis CSA were assessed at pre, 6 weeks and post intervention. The main results showed similar increases in CSA for G40, G60 and G80 groups (25%, 25,1% and 25%, elbow flexors and 20,5%, 20,4% and 19,5% vastus lateralis, respectively, p<0,05). Only the G80 group showed significant difference from G20 group after 12 weeks of resistance training (25% and 14,4%, respectively for elbow flexors and 19,5% and 7,9%, respectively for vastus lateralis, p<0,05). Regarding 1RM the G80 group showed the greatest increase post 12 weeks of resistance training for elbow flexion (54.2% p<0,05) and for leg press 45º the groups G60 and G80 showed the greatest increases (55.4% e 45.7%, respectively, p<0,05). In summary, when different RT intensities (40, 60 and 80% 1RM) performed the same TTV gains of CSA for elbow flexors and vastus lateralis muscles are similar between them and intensities of 20% 1RM did not result a significant increase in CSA. For muscle strength the highest intensities (60% and 80% 1RM) seemed to be superior to promote strength gains than other intensities. These findings indicate that intensities between 40-80% 1RM with equal TTV can elicit significant increase in muscle hypertrophy in upper and lower limbs; however, high intensities are superior to augment strength adaptations in upper and lower limbs

Introdução: O estado de treinamento é um dos fatores que podem influenciar na frequência de treinamento, e de fato, evidências têm sugerido que sujeitos previamente treinados tenham necessidade de realizar o treinamento de força (TF) em maiores frequências semanais, com intuito de aumentar o desempenho de força e a massa muscular. Objetivo: Comparar as alterações no desempenho de força dinâmica máxima (1RM) dos membros inferiores e na área de secção transversa (AST) do músculo quadríceps femoral, após a realização de um programa de treinamento de força distribuído em diferentes frequências semanais, em um grupo de indivíduos previamente treinados em força. Materiais e Métodos: A amostra foi composta por 24 sujeitos do sexo masculino, com idade entre 18 e 35 anos, que participaram de um programa de TF de nove semanas. Os sujeitos foram distribuídos em duas condições: TFVE - treinamento de força com volumes equalizados e, TFVN - treinamento de força com volumes não equalizados. O protocolo de TF utilizou o exercício leg press 45º (unilateral) como único exercício, e deste modo, cada um dos membros inferiores (MMII) foi submetido a uma das frequências semanais de treinamento propostas (i.e., uma e três vezes). O teste de 1RM no exercício leg press 45º (unilateral) e as medidas de AST do músculo quadríceps femoral foram realizados nos momentos pré e pós-treinamento. Resultados: Os aumentos nos valores de 1RM foram significantes (p<0,001) e similares, nas diferentes frequências de TF tanto da condição TFVE (16,0 ± 10,0% e 17,2 ± 12,2% para uma e três vezes por semana, respectivamente) quanto da condição TFVN (19,4 ± 13,1% e 24,6 ± 14,2% para uma e três vezes por semana, respectivamente). Para AST, também houve aumentos significantes (p<0,001) e similares, nas diferentes frequências de TF tanto da condição TFVE (2,1 ± 2,1% e 2,0 ± 2,8% para uma e três vezes por semana, respectivamente) quanto da condição TFVN (1,5 ± 2,6% e 4,1 ± 5,0% para uma e três vezes por semana, respectivamente). Quando o effect size (ES) e o intervalo de confiança (IC) foram calculados, pôde-se observar que a maior frequência de treinamento apresentou melhores resultados nos valores de 1RM e AST, somente quando foi permitida a realização de um maior volume de treinamento (i.e., TFVN). Conclusão: O TF realizado três vezes por semana demonstrou aumentos de 1RM e AST similares àquele realizado somente uma vez, independentemente ou não da equalização do volume de treinamento. Quando a maior frequência de TF pôde proporcionar um maior volume total de treinamento, valores significantes do IC do ES foram observados para ambas as adaptações. Portanto, se indivíduos treinados necessitam de maiores volumes de treinamento para que sejam observados aumentos tanto na força quanto na massa muscular, alternativas como o aumento da frequência do TF podem ser consideradas / Introduction: Training status is one of the factors that may influence training frequency, and in fact, evidence has suggested that previously trained subjects need to perform strength training (ST) at higher weekly frequencies, in order to increase strength and muscle mass. Objective: To compare the changes in lower limbs maximal dynamic strength (1RM) and in the cross-sectional area (CSA) of the quadriceps femoris muscle, after performing a strength training program distributed at different weekly frequencies in a group of previously strength trained individuals. Materials and Methods: The sample was composed of 24 male subjects, aged between 18-35 years, who participated in a 9-week ST program. The subjects were divided into two conditions: STEV - strength training with equalized volumes and, STUV - strength training with unequalized volumes. The ST protocol used the leg press 45º exercise (unilateral) as the only exercise, and thus, each lower limb was submitted to one of the proposed weekly training frequencies (i.e., one and three times). The 1RM test in the leg press 45º exercise (unilateral) and the CSA measurements of the quadriceps femoris muscle were performed at the pre and post training moments. Results: The increases in the 1RM values were significant (p<0.001) and similar, in the different ST frequencies of the STEV condition (16.0 ± 10.0% and 17.2 ± 12.2% for one and three times a week, respectively) and STUV condition (19.4 ± 13.1% and 24.6 ± 14.2% for one and three times a week, respectively). For CSA, there were also similar and significant increases (p<0.001), in the different ST frequencies of the STEV condition (2.1 ± 2.1% and 2.0 ± 2.8% for one and three times a week, respectively) and STUV condition (1.5 ± 2.6% and 4.1 ± 5.0% for one and three times a week, respectively). When the effect size (ES) and the confidence interval (CI) were calculated, it was observed that the higher training frequency presented better results in the 1RM and CSA values, only when it was allowed to perform a higher training volume (i.e., STUV). Conclusion: The ST performed three times a week, showed 1RM and CSA increases similar the one performed only once, regardless of training volume equalization. When the higher frequency of ST allowed a greater total volume of training, significant values of the CI of the ES were observed for both adaptations. Therefore, if trained individuals require higher training volumes to increase strength and muscle mass, alternatives such as increased ST frequency can be considered

Recent advances in genomics now allow for the identification of the genes and mutations that underlie the heritability of agronomically important traits in livestock. The corresponding genes are said to map to Quantitative Trait Loci (QTL), and the mutations referred to as Quantitative Trait Nucleotides (QTN). The most commonly used approach relies on positional cloning which typically proceeds in three steps: QTL mapping by linkage analysis, QTL fine-mapping by linkage disequilibrium or association analysis, and QTN identification combining haplotype analysis and functional assays. Knowledge of QTL and QTN provides insights into the genetic architecture of complex traits and physiology of production traits, and opens novel possibilities for enhanced selection referred to as Marker Assisted Selection (MAS). This thesis is devoted to QTN identification of a QTL that was previously mapped to pig chromosome 2 and fine-mapped to a 250 Kb segment encompassing the imprinted IGF2 gene. The QTL was shown to have a major post-natal effect on muscle mass and fat deposition, and to be subject to parental imprinting as only the padumnal chromosome affects the phenotype. To identify the QTN we have first generated 32 Kb and 56 Kb of finished porcine sequence encompassing the IGF2 and H19 genes, respectively. The corresponding sequences were annotated including definition of gene models, identification of interspersed repeats and determination of 97 sequence elements that are highly conserved between pig, human and mouse. We have then resequenced 28 Kb encompassing the IGF2 gene for 15 boar chromosomes for which the QTL genotype had been determined by progeny-testing or Marker Assisted Segregation Analysis (MASA). This revealed 258 polymorphisms of which only one (Int3-3072G>A) cosegregated perfectly with QTL genotype. The corresponding single nucleotide polymorphism (SNP) is a G to A transition affecting one of the highly conserved sequence elements located just downstream of differentially methylated region 1 in intron 3. We have demonstrated that the Int3-3072 A allele associated with increased muscle mass is also associated with increased IGF2 mRNA levels in post-natal striated muscle (but not in pre-natal muscle nor in pre- and post-natal liver). However, the Int3-3072G>A SNP does not alter imprinting nor allele-specific methylation. Using a luciferase reporter assay, we then demonstrated that the Int3-3072 A allele reduces the cis activity of a silencer element, and using an electrophoretic mobility shift assay (EMSA), that it abrogates binding of a nuclear factor assumed to be a trans-acting silencing factor. Taken together both genetic and functional evidence strongly support the conclusion that the Int3-3072G>A SNP is the causative SNP. The thesis is concluded by a discussion that (i) highlights the factors that make domestic animals a unique resource for the molecular dissection of complex phenotypes, (ii) comments the Asian origin of the Int3-3072A allele associated with increased muscle mass, (iii) describes recent advances in characterizing the trans-acting silencing factor binding to the Int3-3072G allele, (iv) pinpoints statistical issues related to the detection of imprinted QTL, (v) reports on the utility of the Int3-3072G>A SNP for MAS applied to pig breeding, and (vi) makes projections on how latest progress in genome analysis will affect positional identification of QTN in the near future. Grâce aux progrès récents en génomique, il est maintenant possible didentifier les gènes et mutations qui sous-tendent lhéritabilité des caractères de production chez les animaux de rente. Ces gènes se localisent au niveau de Loci de Traits Quantitatifs (QTL), et les mutations correspondantes sont qualifiées de Nucléotides de Traits Quantitatifs (QTN). La démarche expérimentale la plus couramment utilisée est le clonage positionnel. Celui-ci comprend trois étapes: cartographie de QTL par analyses de liaison génétique, cartographie fine de QTL par études dassociation exploitant le déséquilibre de liaison, et identification de QTN par combinaison danalyses haplotypiques et fonctionnelles. Lidentification de QTL et QTN non seulement révèle larchitecture génétique des phénotypes complexes que sont les caractères de production, ainsi que les rouages moléculaires qui les sous-tendent, mais ouvre également des possibilités nouvelles de sélection plus performante dite Assistée par Marqueurs (MAS). Cette thèse est consacrée à lidentification dun QTN correspondant à un QTL dabord localisé sur le chromosome 2 du porc, et ensuite cartographié finement dans un segment chromosomique de 250 Kb comprenant le gène IGF2. Le QTL en question a un effet post-natal majeur sur la croissance musculaire et le dépôt graisseux. Il est soumis à lempreinte parentale, lallèle paternel étant le seul à influencer le phénotype. Afin didentifier le QTN, nous avons tout dabord généré 32 Kb et 56 Kb de séquences finies, comprenant respectivement les gènes IGF2 et H19. Les séquences correspondantes ont été annotées bioinformatiquement, y compris la définition de modèles gèniques, lidentification de séquences répétées dispersées, ainsi que de 97 éléments de séquence fortement conservés chez le porc, lhomme et la souris. Nous avons ensuite re-séquencé 28 Kb chevauchant le gène IGF2 pour 15 chromosomes dont le génotype au niveau du QTL fut préalablement déterminé par testage de descendance ou Ségrégation Assistée par Marqueurs. Cet exercice a révélé 258 polymorphismes dont un seulement (Int3-3072G>A) correspondait parfaitement aux génotypes QTL. Ce polymorphisme est une transition G à A affectant un des 97 éléments hautement conservés, situé juste en aval de la région différentiellement méthylée (DMR1) dans lintron 3. Nous avons ensuite démontré que lallèle Int3-3072 A, associé à une augmentation de la masse musculaire, est également associé à une augmentation des taux dARNm IGF2 dans le muscle strié post-natal (mais non dans le muscle strié pré-natal, ni dans le foie pré- et post-natal). Par contre, le polymorphisme Int3-3072G>A naffecte ni état dempreinte ni de méthylation allèle-spécifique du gène. Nous avons ensuite démontré à laide dun test rapporteur de type luciférase que lallèle Int3-3072 A réduit lactivité dun élément silenceur agissant en cis, et à laide dun test de type EMSA quil empêche la liaison dun facteur nucléaire. Conjointement, ces données génétiques et fonctionnelles démontrent que le polymorphisme Int3-3072G>A SNP correspond bien au QTN. Nous concluons la thèse par une discussion dans laquelle nous (i) démontrons pourquoi les animaux domestiques offrent des possibilités uniques pour la dissection moléculaire de phénotypes complexes, (ii) commentons lorigine asiatique de lallèle Int3-3072A associé à une augmentation du développement musculaire, (iii) décrivons les progrès récent dans lidentification du facteur nucléaire reconnaissant spécifiquement lallèle Int3-3072G, (iv) attirons lattention sur les artéfacts statistiques associés à la détection de QTL soumis à lempreinte, et (v) discutons limpact de nouvelles technologies génomiques sur le clonage positionnel de gènes.