Motivation: Cardiovascular disease (CVD) is one of the leading causes of mortality and morbidity in South Africa and worldwide. Various investigations have confirmed the hypothesis that elevated plasma homocysteine (Hcy) levels may be linked to vascular disease, and it has become clear that hyperhomocysteinemia is an independent risk factor for atherosclerosis and atherothrombosis. Extensive research on the influence of vitamin supplementation leading to the lowering of homocysteine levels has been done, but extensive research on the effect of physical activity on high homocysteine levels is lacking. The interaction of vitamin supplementation in combination with physical activity has also not been investigated. If a conditioning exercise programme can demonstrate a lowering effect on elevated homocysteine levels, it will confirm the importance of physical activity as a less expensive alternative for a better lifestyle that can also continue to lower morbidity and mortality rates. Objective: This study examined the effect of a conditioning program, vitamin supplement and a combination of both on Hcy levels in men with coronary heart disease risk factors. Methods: In a randomized, placebo-controlled, blinded crossover study, 84 men matched for physical activity (PA) levels, age and risk factors were randomly assigned to one of 4 groups [A = physical conditioning, 20-30 min; 70-80% (THR), 8 = physical conditioning + supplement, C = supplement (12,5 ug vitamin 812; 200 ug folic acid) or D = control). Groups A, B, and C were crossed over according to the Latin square design. Total plasma homocysteine, maximal oxygen consumption (V02max) and body composition (BMI & Fat %) were measured before and after each 12-week intervention period. A 6-week washout period separated the crossovers. Results: The experimental and control groups presented similar baseline characteristics and the profile analysis of the V02max values and Hcy concentrations indicated positive results (multivariate p-value <0.0001), due to the fact that the four groups repeated measurements, presented different patterns. A phase effect for the V02max values and a phase and interaction effect for the Hcy concentrations were indicated, though all the subjects were requested to maintain their normal daily routine (eating pattern, PA levels and alcohol consumption) for the duration of the study. The lack of compliance to the conditioning programme makes it impossible to draw conclusions for V02max values. The poor compliance lead to a small sample size that eventually leads to less statistical power. Conclusion: This study found that a 12-week conditioning programme had no effect on Hcy concentrations. The results of this study make it impossible, due to poor compliance, to suggest that the effect of increased PA on homocysteine may play an important role in the prevention and treatment of CVD. It is, therefore, recommended that more studies should be conducted to further investigate the effect of PA and vitamin supplements on tHcy levels. / Thesis (M.Sc. (Human Movement Science))--North-West University, Potchefstroom Campus, 2006.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Motivation: Cardiovascular disease (CVD) is one of the leading causes of mortality and morbidity in South Africa and worldwide. Various investigations have confirmed the hypothesis that elevated plasma homocysteine (Hcy) levels may be linked to vascular disease, and it has become clear that hyperhomocysteinemia is an independent risk factor for atherosclerosis and atherothrombosis. Extensive research on the influence of vitamin supplementation leading to the lowering of homocysteine levels has been done, but extensive research on the effect of physical activity on high homocysteine levels is lacking. The interaction of vitamin supplementation in combination with physical activity has also not been investigated. If a conditioning exercise programme can demonstrate a lowering effect on elevated homocysteine levels, it will confirm the importance of physical activity as a less expensive alternative for a better lifestyle that can also continue to lower morbidity and mortality rates. Objective: This study examined the effect of a conditioning program, vitamin supplement and a combination of both on Hcy levels in men with coronary heart disease risk factors. Methods: In a randomized, placebo-controlled, blinded crossover study, 84 men matched for physical activity (PA) levels, age and risk factors were randomly assigned to one of 4 groups [A = physical conditioning, 20-30 min; 70-80% (THR), 8 = physical conditioning + supplement, C = supplement (12,5 ug vitamin 812; 200 ug folic acid) or D = control). Groups A, B, and C were crossed over according to the Latin square design. Total plasma homocysteine, maximal oxygen consumption (V02max) and body composition (BMI & Fat %) were measured before and after each 12-week intervention period. A 6-week washout period separated the crossovers. Results: The experimental and control groups presented similar baseline characteristics and the profile analysis of the V02max values and Hcy concentrations indicated positive results (multivariate p-value <0.0001), due to the fact that the four groups repeated measurements, presented different patterns. A phase effect for the V02max values and a phase and interaction effect for the Hcy concentrations were indicated, though all the subjects were requested to maintain their normal daily routine (eating pattern, PA levels and alcohol consumption) for the duration of the study. The lack of compliance to the conditioning programme makes it impossible to draw conclusions for V02max values. The poor compliance lead to a small sample size that eventually leads to less statistical power. Conclusion: This study found that a 12-week conditioning programme had no effect on Hcy concentrations. The results of this study make it impossible, due to poor compliance, to suggest that the effect of increased PA on homocysteine may play an important role in the prevention and treatment of CVD. It is, therefore, recommended that more studies should be conducted to further investigate the effect of PA and vitamin supplements on tHcy levels. / Thesis (M.Sc. (Human Movement Science))--North-West University, Potchefstroom Campus, 2006.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal. / Le premier objectif de ce travail était de faire une revue des études disponibles dans la littérature sur la relation entre la puissance relative (% du VO₂max) et la durée du travail jusqu'à épuisement (Tlim, min). Cette revue permet d'établir la relation entre le % VO₂max et Tlim pour une étendue de temps de travail allant de 1,3 à 240 min : % RAM = 93,76 - 55,60 x log (log Tlim) ou % PAM = 94,37 - 54,47 x log (log Tlim) selon que l'on utilise les données des études ayant rapporté un ou plusieurs couples % PAM-Tlim, ou ayant modélisé la relation % PAM-Tlim. Le fait que ces deux équations soient très voisines bien qu'elles dérivent de deux ensembles de données expérimentales totalement indépendantes, est un gage de leur validité. La valeur de Tlim pour une PAM donnée pourrait être un peu plus basse sur ergocycle que sur tapis roulant ou à la course sur le terrain, au moins pour les valeurs élevées de Tlim. Elles sont aussi plus basses en laboratoire ou lors d'une évaluation sur le terrain qu'en compétition. Par contre, elles ne semblent pas être différentes selon les sexes. Enfin, elles pourraient être un peu plus hautes pour les sujets qui ont un VO₂max élevé. L'étude expérimentale, qui a porté sur dix coureurs à pied de niveau récréatif (33,1 ± 5,6 ans, 174,1 ± 3,6 cm, 69,1 ± 6,9 kg, VO₂max sur tapis roulant et ergocycle : 60,4 ± 4,7 et 59,6 ± 5,9 mL.kg⁻¹.min⁻¹), montre que les Tlim à 100 % VO₂max ne sont pas significativement différents sur tapis roulant et sur ergocycle (388 ± 71 et 386 ± 51 s). Comme l'ont montré Billat et al. (1994 a), la valeur moyenne de Tlim à 100 % VO₂max est donc très reproductible. Toutefois, l'étendue des valeurs de Tlim sur chacun des deux ergomètres est importante, comme cela a été aussi observé dans toutes les études sur cette question. En outre, nous ne trouvons pas de relation entre les valeurs de Tlim sur les deux ergomètres, contrairement aux résultats de Billat et al. (1994 a), qui ont observé une relation significative entre les valeurs de Tlim mesurées à deux reprises. Billat et al. (1994 a et b, 1995 a et b, 1996) ont aussi observé dans certains cas des relations entre Tlim à 100 % de la PAM et diverses autres caractéristiques bioénergétiques, comme le VO₂max, la vitesse aérobie maximale, et des indices de la capacité anaérobie et de l'endurance. Ces relations ne sont pas toujours consistantes et nous ne les avons pas retrouvées dans notre étude. Par contre, l'analyse de toutes les données de la littérature suggère que Tlim à 100 % du VO₂max pourrait être effectivement relié de façon inverse au VO₂max et à la VAM. Prises dans leur ensemble, les données de Billat et al. (1994 a) et nos propres données sur la fidélité de Tlim à 100 % de la PAM montrent que la mesure de cette variable est reproductible dans un groupe de sujets, mais ne l'est pas de façon convenable pour un sujet pris individuellement : les risques d'erreurs étant beaucoup trop grands. Ceci empêche de pouvoir actuellement considérer la valeur de Tlim à 100 % du VO₂max comme une variable d'intérêt dans l'évaluation de l'athlète et dans le suivi de son entraînement.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal