Self-Control Training (SCT) and Brain Endurance Training (BET) are novel training modalities designed to enhance physical endurance by building fatigue resiliency. Despite their similarities, it has yet to be examined whether combining SCT and BET provides an additive or redundant/overlapping effect on endurance exercise performance. This study investigated the effects of SCT and combined SCT+BET on performance of a maximal exertion isometric resistance endurance task (high plank) and ratings of perceived exertion (RPE). Participants (N = 33) were randomized to engage in 4 weeks (18 training sessions) of SCT (isometric handgrip; n = 13), SCT+BET (10-minute cognitively demanding task, followed by SCT; n = 10), or no-training/control (n = 10). Isometric endurance performance trials were completed at pre-, mid-, and post-training. One-way analysis of covariance (ANCOVA) models were computed for each of the mid- and post-training trials (controlling for pre-training high-plank performance) to assess effects on performance. Results showed no significant effects of training on high plank performance between groups at mid-training; however, a large and significant effect for SCT compared to control was observed at post-training (p = .044, d = .961). No significant main effects or interaction effects were found for changes in RPE over time (p’s > .05). Findings support the use of SCT as an effective training method for physical endurance performance and suggest that BET may not offer additional performance benefit compared to SCT under the training and testing conditions used in this protocol. Future research should explore potential dose-response effects of SCT on performance and moderators such as trait self-control. / Thesis / Master of Science (MSc)

Skeletal muscle is a primary contributor to body mass and whole-body energy metabolism. It is an adaptive tissue with the ability to fluctuate in size and mechanical properties in response to stimulus. Health conditions involving chronic elevated inflammation levels often feature metabolic inflexibility and losses in skeletal muscle mass. Mononuclear stem cells, termed satellite cells, are mitotic and serve to donate nuclei to muscle fibers to enable skeletal muscle adaptation. Despite the well-characterized nature of satellite cell activation, proliferation, and differentiation, the underlying mechanisms regulating this process is not fully understood. Recent characterization of cytokines secreted by skeletal muscle in an endocrine type fashion has led to discoveries of inflammatory cytokines influencing satellite cell function. However, how the autocrine production and secretion of these cytokines during proliferation and differentiation in humans and their correlation with myogenic transcription factors is not well understood. Our study used satellite cells cultured from the vastus lateralis of 12 male human research subjects, and ELISA analysis to measure levels of TNF-α and IL-6 across proliferation, early differentiation, and late differentiation. Additionally, mRNA levels of Pax7, MyoD, myogenin, IL-6, TNF-α, and TGF-β were assessed in satellite cells cultured from a subset of two endurance trained and two sedentary individuals from the larger group of 12 human subjects. The novelty of our study is the large number of human research subjects and simultaneous analysis of inflammatory cytokine secretion, mRNA inflammatory cytokine expression, and myogenic transcription factor mRNA expression. Results showed an 83% decrease in IL-6 protein secretion 24 hours after exposure to differentiation media (p-value <0.05) before increasing 50-fold after 7 day of exposure to differentiation media (p-value < 0.05). Myogenin and TGF-β mRNA expression levels were positively correlated (R2 = 0.5814, p-value < 0.0001). A negative correlation was found between IL-6 and MyoD (R2 = 0.2473, p – value = 0.0257). After 1 day of exposure to differentiation media, satellite cells from endurance trained subjects exhibited higher levels of TGF-β mRNA expression compared to sedentary satellite cells of sedentary subjects of the same age and levels of adiposity (p-value < 0.05). Results support a potential relationship in humans satellite cells between myogenic transcription factors and inflammatory cytokines, however, further study is necessary in order to investigate the underlying mechanisms behind the correlations. / Master of Science / Skeletal muscle is responsible for conscious, voluntary movement. In addition, the tissue is responsible for the majority of energy expenditure in the human body. Skeletal muscle is able to adapt to exercise programs through the fusion of undifferentiated stem cells – called satellite cells – in the skeletal muscle fiber. In long-term diseased conditions, the immune response involves chronic rises in inflammation and results in the loss of skeletal muscle and corresponding loss of ability to move. A shorter rise in inflammation is also linked with the positive exercise response. Our study features satellite cells harvested from muscle samples of 12 male human research participants. We were interested in evaluating the relationships between the expression and secretion of two proteins associated with inflammation and regulation of the satellite cell cycle. The two proteins of interest in our study are tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). We also measure the gene expression of another inflammatory protein, transforming growth factor beta (TGF-β). In order to know where the cells were in their life cycle, we measured expression of genes associated with the division (Pax7), early fusion (MyoD), and late fusion of satellite cells (myogenin). Our study found a decrease in IL-6 secretion and expression as the process of satellite cells turning into muscle fibers was initiated. Additionally, a 50-fold increase in IL-6 expression was found at day 7 compared to day 0 of the satellite cell cycle. Additionally, we found a positive correlation between TGF-β and myogenin and a negative correlation between IL-6 and MyoD. Although we found correlations between satellite cell cycle genes and inflammation genes, more research is necessary to see if there is a pathway causing this relationship.

Obesity is associated with reduced skeletal muscle insulin sensitivity, a major risk factor for development of type II diabetes. These metabolic diseases are commonly associated with an accumulation of mitochondrial dysfunction, which is speculated to contribute toward insulin resistance. High-fat diets reduce human skeletal muscle insulin sensitivity and mitochondrial function. Conversely, endurance training increases insulin sensitivity and enhances mitochondrial performance. Recent evidence in mice has found that central mechanisms of mitochondrial quality control, autophagy and mitophagy, may be suppressed in response to excess fat intake, but upregulated following endurance exercise training. These data may provide a mechanism for dietary and exercise-mediated regulation of mitochondrial quality and metabolic function. The current study investigated the impact of an acute high-fat diet on skeletal muscle autophagy and mitophagy in sedentary, healthy, non-obese college age males'. The expression of skeletal muscle autophagy and mitophagy protein markers were analyzed in response to a high-fat meal before and after a 5-day high-fat diet. Next, we examined the differences in skeletal muscle autophagy and mitophagy protein markers, and associations with skeletal muscle metabolic flexibility between endurance-trained male runners' and sedentary, healthy, non-obese males' following an overnight fast and in response to a high-fat meal. Autophagy markers' indicated reduced autophagy activity in response to a high-fat meal and following a high-fat diet, which exacerbated the high-fat meal response. However, these data could not be confirmed due to methodological limitations. Mitophagy markers were not significantly affected by the high-fat meal or diet. There were no significant differences in the expression of autophagy protein markers between endurance-trained and sedentary groups', but mitophagy markers were significantly elevated in endurance-trained runners'. Metabolic flexibility was not significantly different between groups' following an overnight fast or in response to a high-fat meal, and was not associated with the expression of autophagy and mitophagy protein markers. In conclusion, autophagy may be suppressed by a 5-day high-fat diet, but further analysis is required for confirmation. Endurance-trained male runners show increased markers of mitophagy, which were not associated with improved metabolic flexibility while fasted or following a high-fat meal. / Ph. D.

In healthy individuals, satellite cells are partly responsible for muscle repair and preventing atrophy. Previous studies have linked the loss of muscle mass associated with aging to satellite cell dysfunction, postulating that satellite cell function diminishes with age. New evidence suggests that this may not be true as satellite cells collected from healthy aged participants appear indistinguishable from their healthy young counterparts. Satellite cell dysfunction appears to be more mechanistically linked to poor lifestyle factors such as low physical activity, improper diet, and increased adiposity. For this study, satellite cell function was evaluated against the effects of aging, diet, activity level, and adiposity. Satellite cells were collected from the vastus lateralis of sedentary (<2 hours/week activity) male donors categorized into young (18-30 years) and older (60-80 years) groups, as well as a young endurance trained group (18-30 years, 5+ hours/week of running/cycling). Cells were collected in young sedentary males before and after a four-week, high fat (55% of kcal), and hypercaloric (+1000 kcal over DEE) diet (HFHCD). Cells were also subjected to an in-vitro, high substrate media (HSM) challenge, then grown in media with a fivefold increase in glucose (25 mM) and an additional 400 uM of fatty acids (2:1 palmitate:oleate) before seven days of serum starved differentiation. The cells were evaluated for their proliferation rate, ability to differentiate (fusion index), rate of reactive oxygen species (ROS) production, and capacity for substrate oxidation (glucose and fatty acid). The young group exhibited a lower proportion of body fat than the older group (22.4%±8.1 vs. 28.3%±6.3). When compared to the older group, the young group also presented elevated oxidative efficiency (68%, p<0.05) and reduced pyruvate oxidation (-60%, p<0.05) in measures of muscle tissue homogenate. However, isolated satellite cells from the young and older group demonstrated no observable differences in any measures (proliferation rate, fusion index, ROS production, or substrate oxidation), other than increased oxidative efficiency in cells from older vs. younger donors. Cells from young endurance trained donors demonstrated faster proliferation rates (39%, p<0.05) and elevated early stage fusion (33%, p<0.05) when compared to cells from older individuals. Compared to pre-diet measures, cells collected post HFHCD revealed significantly reduced proliferation rates (-19%, p<0.05). When grown in HSM (as compared to control media), cells from young lean (<25% BF) and trained participants had blunted proliferation rates (-4.8% and -12.6%, p<0.05), fusion index scores (p<0.05), and ROS production rates. Cells collected from participants with higher adiposity (>25% BF) and those collected post HFHCD experienced increased proliferation and fusion when exposed to the HSM. This data suggests that donor activity level, adiposity, and diet but not age are mediating factors for satellite cell function. The cells appear to develop a preference for their in-vivo environment, as cells collected from the leaner and trained participants had their proliferation and fusion rates reduced when exposed to HSM. Conversely, exposure to the HSM accelerated the proliferation and fusion of cells collected from donors with higher body fat and those collected post HFHCD. / PHD / The continually active nature of muscle tissue leaves it vulnerable to physical and chemical damage. Any physical activity especially exercise can cause numerous sites of micro-damage to the muscle tissue. To maintain function, damaged muscle tissue is continually remodeled throughout lifespan. To replace damaged muscle tissue, a special type of muscle specific stem cell, termed a satellite cell, is utilized. Satellite cells lay dormant inside the muscle tissue until their activity is promoted by signals that result from muscle injury. Once activated, satellite cells develop into new muscle cells, a process known as myogenesis. Proper function of satellite cells is required for our muscle tissue to respond to injury. Past studies have demonstrated that aging adversely impacts satellite cell activity, which is thought to contribute to loss of muscle mass and strength typically observed with aging. However, newer evidence suggest that an unhealthy diet and a sedentary lifestyle may contribute to satellite cell dysfunction. This study studied satellite cell function to determine if aging, sedentary life style, and unhealthy diet contributed to satellite cell dysfunction. The results demonstrated that age had no effect on any measures of satellite cell function. Findings suggested that a sedentary lifestyle resulted in diminished satellite cell function regardless of age. This study demonstrated that four weeks on a high-fat/high-calorie “western style” diet decreased satellite cell function. It was also demonstrated that exposing satellite cells to a high-sugar/high-fat treatment altered their cellular function. These data suggest that alterations in macronutrient content of a person’s diet may adversely impact satellite cell function, and decrease the potential for myogenesis. In conclusion aging had no effect satellite cell function. A high-fat/high-calorie diet and sedentary lifestyle did contribute to satellite cell dysfunction. It appears that the loss of muscle mass and strength observed in aged individuals is not associated with satellite cell function.

In this study the effects of age (18-55 years), differing levels of fitness (VO 2max ranging from 35.5 to 68.8ml.kg-1.min-1) and endurance training (10 weeks) on heart rate control were investigated. Fitness level was initially determined by a VO2max stress test, succeeded by cold hand and cold face pressor test of autonomic activity. Following these baseline measurements, the subjects (32 nonsmoking male volunteers) were endurance-trained three to four times a week for a 10-week period. The baseline tests were readministered following the 10-week dynamic exercise training period. These data suggest that a natural consequence of aging is a diminishment of autonomic heart rate control; however, endurance training appears to interrupt the aging influence. Individuals of low fitness level appear to have heart rate control dominated by the sympathetic system, while individuals with high fitness levels have a vagally dominated heart rate control system.

The research presented in this thesis examined the issue of the compatibility of strength and endurance training within one training regime, termed concurrent training, in recreational cyclists. Various research designs used in the previous literature resulted in inconclusive findings. The overall aim of this thesis was therefore to examine, in three systematically designed studies, the effects of various components of concurrent training regimes on cycling efficiency and recovery, and to identify some of the mechanisms that may be responsible for the interference or impedance of strength and/or endurance adaptations.

The research presented in this thesis examined the issue of the compatibility of strength and endurance training within one training regime, termed concurrent training, in recreational cyclists. Various research designs used in the previous literature resulted in inconclusive findings. The overall aim of this thesis was therefore to examine, in three systematically designed studies, the effects of various components of concurrent training regimes on cycling efficiency and recovery, and to identify some of the mechanisms that may be responsible for the interference or impedance of strength and/or endurance adaptations.

O sistema cardiovascular pode adaptar-se ao treinamento. Pouco se sabe sobre a influência do treinamento sobre a regulação autonômica, estrutura cardíaca e função em crianças e adolescentes atletas. O objetivo deste estudo foi avaliar a estrutura e função do ventrículo esquerdo em nadadores adolescentes. Foram comparados 28 atletas nadadores entre 15 e 17 anos (15 meninos e 13 meninas), que nadavam entre 25 km e 45 km/semana, nos últimos 2 anos, com grupo controle de 28 adolescentes (14 meninos e 14 meninas) com idade, peso e altura similares. Foi realizado ecocardiograma bidimensional e modo-M para avaliação cardiológica. Foram avaliados: diâmetro interno do ventrículo esquerdo durante a sístole (VES), diâmetro interno do ventrículo esquerdo durante a diástole (VED), septo interventricular (S), parede posterior do ventrículo esquerdo (PP), através da ecocardiografia modo-M. A massa do ventrículo esquerdo (MVE), índice de massa do VE, fração de encurtamento (ΔD) e fração de ejeção (FE) foram calculadas. Parâmetros diastólicos incluindo a velocidade do fluxo pela valva mitral e pelas veias pulmonares foram medidos: velocidade de enchimento rápido (pico da onda E), e tardio (pico da onda A), relação E/A, tempo de relaxamento isovolumétrico (TRIV) e tempo de desaceleração (TD), velocidade da onda de fluxo sistólico e diastólico pulmonar. Para comparar os dois grupos foi utilizando Teste t de Student para amostras independentes. Não foram encontradas diferenças antropométricas significativas entre os grupos. Comparado com o controle, nadadores do sexo masculino apresentaram uma diferença significativamente maior nas medidas do diâmetro interno do VED (53,6 ± 4,3 mm, p = 0,009), na espessura do septo interventricular (7,9 ± 1 mm, p = 0,0001) e da espessura da parede posterior do ventrículo esquerdo (7,90 ± 1,3 mm vs. 6,4 ± 0,08 mm, p = 0,001) e aumento da massa do VE (192,7 ± 54,7 g vs. 128,7 ± 28,6 g, p = 0,001). As nadadoras do sexo feminino apresentaram um significante aumento do diâmetro interno do VED (48 ± 3,7 vs. 45 ± 2,4 mm, p = 0,007), mas não houve diferenças nas medidas de S e PP, nem da massa do VE. Os parâmetros de fluxo transmitral foram semelhantes em ambos os grupos, exceto pelo prolongamento do TD nos nadadores (220 ± 47 vs. 181 ± 20 ms, p = 0,008 no sexo masculino, e 227 ± 50 vs. 177 ± 31 ms, p = 0,004 no sexo feminino). Estes achados sugerem que o treinamento de natação por um período prolongado em adolescentes causa aumento do tamanho e da massa do VE, mantendo a função sistólica normal e melhorando a complacência ventricular. A hipertrofia do VE com aumento da complacência ventricular é característico da adaptação fisiológica ao treinamento de endurance. Os parâmetros de fluxo transmitral foram semelhantes em ambos os grupos, exceto pelo prolongamento do TD nos nadadores (220 ± 47 vs. 181 ± 20 ms, p = 0,008 no sexo masculino, e 227 ± 50 vs. 177 ± 31 ms, p = 0,004 no sexo feminino). Estes achados sugerem que o treinamento de natação por um período prolongado em adolescentes causa aumento do tamanho e da massa do VE, mantendo a função sistólica normal e melhorando a complacência ventricular. A hipertrofia do VE com aumento da complacência ventricular é característico da adaptação fisiológica ao treinamento de endurance. / The cardiovascular system can adapt to aerobic training. Little is known about the influence of training on autonomic regulation and cardiac structure and function in children and adolescent athletes. The purpose of the present study was to evaluate left ventricular structure and function in adolescent swimmers. We compared 28 eight swimmers between 15 and 17 years old (15 boys and 13 girls), training between 25 km to 45 km /week for the last three years and 28 non training control subjects (14 boys and 14 girls) similar in age, weight and height of the athletes. Two-dimensional, M-mode and Doppler-echocardiography were performed. Left ventricular internal diameters in diastole (LVIDd) and systole (LVIDs), interventricular septum thickness (IVS), left ventricular posterior wall (LVPW) were measured from M-mode echocardiography. Left ventricular mass (LVM), LVM index, shortening fraction (SF) and ejection fraction (EF) were calculated. Diastolic parameters including mitral valve inflow velocities and pulmonary vein flow were measured: maximal early (peak E wave), and late (peak A wave) mitral velocities, E/A ratio, isovolumic relaxation time (IVRT) and deceleration time (DT), pulmonary systolic (S), diastolic (D) and Ar wave velocities. Comparisons between the two groups were made using the independent samples Student t-test. There were no significant anthropometric differences between the two groups. Compared with controls, male swimmers showed a significantly greater LVIDd (53.6 ± 4.3 mm, p < 0.009), a thicker IVS (7.9 ± 1 mm, p < 0.0001) and LVPW (7.90 ± 1.3 mm vs. 6.4 ± 0.08 mm, p < 0,001), an increased LVM (192.7 ± 54.7 g vs. 128.7 ± 28.6 g, p < 0.001). Female swimmers had a significanty greater LVIDd (48 ± 3.7 vs. 45 ± 2.4 mm, p < 0.007), but no greater IVS or LVPW thickness, neither LVM. SF and EF were similar in both groups. Transmitral inflow parameters were similar in both groups, except for a prolonged TD in the swimmers group (220 ± 47 vs. 181 ± 20 ms, p < 0.008 in males and 227 ± 50 vs. 177 ± 31 ms, p < 0.004 in females). These findings suggest that long-term swimming in adolescents promotes increase in left ventricular size and mass with normal systolic function and improved diastolic compliance. LV hypertrophy with an improved compliance is characteristic of physiological adaptation of endurance training.

O sistema cardiovascular pode adaptar-se ao treinamento. Pouco se sabe sobre a influência do treinamento sobre a regulação autonômica, estrutura cardíaca e função em crianças e adolescentes atletas. O objetivo deste estudo foi avaliar a estrutura e função do ventrículo esquerdo em nadadores adolescentes. Foram comparados 28 atletas nadadores entre 15 e 17 anos (15 meninos e 13 meninas), que nadavam entre 25 km e 45 km/semana, nos últimos 2 anos, com grupo controle de 28 adolescentes (14 meninos e 14 meninas) com idade, peso e altura similares. Foi realizado ecocardiograma bidimensional e modo-M para avaliação cardiológica. Foram avaliados: diâmetro interno do ventrículo esquerdo durante a sístole (VES), diâmetro interno do ventrículo esquerdo durante a diástole (VED), septo interventricular (S), parede posterior do ventrículo esquerdo (PP), através da ecocardiografia modo-M. A massa do ventrículo esquerdo (MVE), índice de massa do VE, fração de encurtamento (ΔD) e fração de ejeção (FE) foram calculadas. Parâmetros diastólicos incluindo a velocidade do fluxo pela valva mitral e pelas veias pulmonares foram medidos: velocidade de enchimento rápido (pico da onda E), e tardio (pico da onda A), relação E/A, tempo de relaxamento isovolumétrico (TRIV) e tempo de desaceleração (TD), velocidade da onda de fluxo sistólico e diastólico pulmonar. Para comparar os dois grupos foi utilizando Teste t de Student para amostras independentes. Não foram encontradas diferenças antropométricas significativas entre os grupos. Comparado com o controle, nadadores do sexo masculino apresentaram uma diferença significativamente maior nas medidas do diâmetro interno do VED (53,6 ± 4,3 mm, p = 0,009), na espessura do septo interventricular (7,9 ± 1 mm, p = 0,0001) e da espessura da parede posterior do ventrículo esquerdo (7,90 ± 1,3 mm vs. 6,4 ± 0,08 mm, p = 0,001) e aumento da massa do VE (192,7 ± 54,7 g vs. 128,7 ± 28,6 g, p = 0,001). As nadadoras do sexo feminino apresentaram um significante aumento do diâmetro interno do VED (48 ± 3,7 vs. 45 ± 2,4 mm, p = 0,007), mas não houve diferenças nas medidas de S e PP, nem da massa do VE. Os parâmetros de fluxo transmitral foram semelhantes em ambos os grupos, exceto pelo prolongamento do TD nos nadadores (220 ± 47 vs. 181 ± 20 ms, p = 0,008 no sexo masculino, e 227 ± 50 vs. 177 ± 31 ms, p = 0,004 no sexo feminino). Estes achados sugerem que o treinamento de natação por um período prolongado em adolescentes causa aumento do tamanho e da massa do VE, mantendo a função sistólica normal e melhorando a complacência ventricular. A hipertrofia do VE com aumento da complacência ventricular é característico da adaptação fisiológica ao treinamento de endurance. Os parâmetros de fluxo transmitral foram semelhantes em ambos os grupos, exceto pelo prolongamento do TD nos nadadores (220 ± 47 vs. 181 ± 20 ms, p = 0,008 no sexo masculino, e 227 ± 50 vs. 177 ± 31 ms, p = 0,004 no sexo feminino). Estes achados sugerem que o treinamento de natação por um período prolongado em adolescentes causa aumento do tamanho e da massa do VE, mantendo a função sistólica normal e melhorando a complacência ventricular. A hipertrofia do VE com aumento da complacência ventricular é característico da adaptação fisiológica ao treinamento de endurance. / The cardiovascular system can adapt to aerobic training. Little is known about the influence of training on autonomic regulation and cardiac structure and function in children and adolescent athletes. The purpose of the present study was to evaluate left ventricular structure and function in adolescent swimmers. We compared 28 eight swimmers between 15 and 17 years old (15 boys and 13 girls), training between 25 km to 45 km /week for the last three years and 28 non training control subjects (14 boys and 14 girls) similar in age, weight and height of the athletes. Two-dimensional, M-mode and Doppler-echocardiography were performed. Left ventricular internal diameters in diastole (LVIDd) and systole (LVIDs), interventricular septum thickness (IVS), left ventricular posterior wall (LVPW) were measured from M-mode echocardiography. Left ventricular mass (LVM), LVM index, shortening fraction (SF) and ejection fraction (EF) were calculated. Diastolic parameters including mitral valve inflow velocities and pulmonary vein flow were measured: maximal early (peak E wave), and late (peak A wave) mitral velocities, E/A ratio, isovolumic relaxation time (IVRT) and deceleration time (DT), pulmonary systolic (S), diastolic (D) and Ar wave velocities. Comparisons between the two groups were made using the independent samples Student t-test. There were no significant anthropometric differences between the two groups. Compared with controls, male swimmers showed a significantly greater LVIDd (53.6 ± 4.3 mm, p < 0.009), a thicker IVS (7.9 ± 1 mm, p < 0.0001) and LVPW (7.90 ± 1.3 mm vs. 6.4 ± 0.08 mm, p < 0,001), an increased LVM (192.7 ± 54.7 g vs. 128.7 ± 28.6 g, p < 0.001). Female swimmers had a significanty greater LVIDd (48 ± 3.7 vs. 45 ± 2.4 mm, p < 0.007), but no greater IVS or LVPW thickness, neither LVM. SF and EF were similar in both groups. Transmitral inflow parameters were similar in both groups, except for a prolonged TD in the swimmers group (220 ± 47 vs. 181 ± 20 ms, p < 0.008 in males and 227 ± 50 vs. 177 ± 31 ms, p < 0.004 in females). These findings suggest that long-term swimming in adolescents promotes increase in left ventricular size and mass with normal systolic function and improved diastolic compliance. LV hypertrophy with an improved compliance is characteristic of physiological adaptation of endurance training.

O sistema cardiovascular pode adaptar-se ao treinamento. Pouco se sabe sobre a influência do treinamento sobre a regulação autonômica, estrutura cardíaca e função em crianças e adolescentes atletas. O objetivo deste estudo foi avaliar a estrutura e função do ventrículo esquerdo em nadadores adolescentes. Foram comparados 28 atletas nadadores entre 15 e 17 anos (15 meninos e 13 meninas), que nadavam entre 25 km e 45 km/semana, nos últimos 2 anos, com grupo controle de 28 adolescentes (14 meninos e 14 meninas) com idade, peso e altura similares. Foi realizado ecocardiograma bidimensional e modo-M para avaliação cardiológica. Foram avaliados: diâmetro interno do ventrículo esquerdo durante a sístole (VES), diâmetro interno do ventrículo esquerdo durante a diástole (VED), septo interventricular (S), parede posterior do ventrículo esquerdo (PP), através da ecocardiografia modo-M. A massa do ventrículo esquerdo (MVE), índice de massa do VE, fração de encurtamento (ΔD) e fração de ejeção (FE) foram calculadas. Parâmetros diastólicos incluindo a velocidade do fluxo pela valva mitral e pelas veias pulmonares foram medidos: velocidade de enchimento rápido (pico da onda E), e tardio (pico da onda A), relação E/A, tempo de relaxamento isovolumétrico (TRIV) e tempo de desaceleração (TD), velocidade da onda de fluxo sistólico e diastólico pulmonar. Para comparar os dois grupos foi utilizando Teste t de Student para amostras independentes. Não foram encontradas diferenças antropométricas significativas entre os grupos. Comparado com o controle, nadadores do sexo masculino apresentaram uma diferença significativamente maior nas medidas do diâmetro interno do VED (53,6 ± 4,3 mm, p = 0,009), na espessura do septo interventricular (7,9 ± 1 mm, p = 0,0001) e da espessura da parede posterior do ventrículo esquerdo (7,90 ± 1,3 mm vs. 6,4 ± 0,08 mm, p = 0,001) e aumento da massa do VE (192,7 ± 54,7 g vs. 128,7 ± 28,6 g, p = 0,001). As nadadoras do sexo feminino apresentaram um significante aumento do diâmetro interno do VED (48 ± 3,7 vs. 45 ± 2,4 mm, p = 0,007), mas não houve diferenças nas medidas de S e PP, nem da massa do VE. Os parâmetros de fluxo transmitral foram semelhantes em ambos os grupos, exceto pelo prolongamento do TD nos nadadores (220 ± 47 vs. 181 ± 20 ms, p = 0,008 no sexo masculino, e 227 ± 50 vs. 177 ± 31 ms, p = 0,004 no sexo feminino). Estes achados sugerem que o treinamento de natação por um período prolongado em adolescentes causa aumento do tamanho e da massa do VE, mantendo a função sistólica normal e melhorando a complacência ventricular. A hipertrofia do VE com aumento da complacência ventricular é característico da adaptação fisiológica ao treinamento de endurance. Os parâmetros de fluxo transmitral foram semelhantes em ambos os grupos, exceto pelo prolongamento do TD nos nadadores (220 ± 47 vs. 181 ± 20 ms, p = 0,008 no sexo masculino, e 227 ± 50 vs. 177 ± 31 ms, p = 0,004 no sexo feminino). Estes achados sugerem que o treinamento de natação por um período prolongado em adolescentes causa aumento do tamanho e da massa do VE, mantendo a função sistólica normal e melhorando a complacência ventricular. A hipertrofia do VE com aumento da complacência ventricular é característico da adaptação fisiológica ao treinamento de endurance. / The cardiovascular system can adapt to aerobic training. Little is known about the influence of training on autonomic regulation and cardiac structure and function in children and adolescent athletes. The purpose of the present study was to evaluate left ventricular structure and function in adolescent swimmers. We compared 28 eight swimmers between 15 and 17 years old (15 boys and 13 girls), training between 25 km to 45 km /week for the last three years and 28 non training control subjects (14 boys and 14 girls) similar in age, weight and height of the athletes. Two-dimensional, M-mode and Doppler-echocardiography were performed. Left ventricular internal diameters in diastole (LVIDd) and systole (LVIDs), interventricular septum thickness (IVS), left ventricular posterior wall (LVPW) were measured from M-mode echocardiography. Left ventricular mass (LVM), LVM index, shortening fraction (SF) and ejection fraction (EF) were calculated. Diastolic parameters including mitral valve inflow velocities and pulmonary vein flow were measured: maximal early (peak E wave), and late (peak A wave) mitral velocities, E/A ratio, isovolumic relaxation time (IVRT) and deceleration time (DT), pulmonary systolic (S), diastolic (D) and Ar wave velocities. Comparisons between the two groups were made using the independent samples Student t-test. There were no significant anthropometric differences between the two groups. Compared with controls, male swimmers showed a significantly greater LVIDd (53.6 ± 4.3 mm, p < 0.009), a thicker IVS (7.9 ± 1 mm, p < 0.0001) and LVPW (7.90 ± 1.3 mm vs. 6.4 ± 0.08 mm, p < 0,001), an increased LVM (192.7 ± 54.7 g vs. 128.7 ± 28.6 g, p < 0.001). Female swimmers had a significanty greater LVIDd (48 ± 3.7 vs. 45 ± 2.4 mm, p < 0.007), but no greater IVS or LVPW thickness, neither LVM. SF and EF were similar in both groups. Transmitral inflow parameters were similar in both groups, except for a prolonged TD in the swimmers group (220 ± 47 vs. 181 ± 20 ms, p < 0.008 in males and 227 ± 50 vs. 177 ± 31 ms, p < 0.004 in females). These findings suggest that long-term swimming in adolescents promotes increase in left ventricular size and mass with normal systolic function and improved diastolic compliance. LV hypertrophy with an improved compliance is characteristic of physiological adaptation of endurance training.