Cardiovascular disease is one of the leading causes of death and disability, and is responsible for approximately one third of all deaths. Conversely, effective functioning of the heart is critical for performance in many sports and recreational activities. Therefore, developing effective strategies for preventing cardiovascular disease and promoting enhanced function of the heart is paramount. The overarching purpose of this thesis was to evaluate how cardiac muscle develops and ways to improve its function through dietary and exercise intervention.

The work of this thesis was conducted in three phases. In the first phase, we compared both the structural and mechanical adaptations of the heart in response to aerobic and resistance exercise training. We concluded that exercise affects the structure and function of the heart, and its cellular components in a manner that is specific to the exercise protocol, and that there may be additional benefit of combining aerobic and resistance exercise training. In the second phase, we evaluated the effects of systematic protein supplementation in addition to aerobic exercise on the structural and mechanical properties of the heart. We concluded from these findings that a whey supplemented high-protein diet did not provide additional benefit for cardiac adaptation following aerobic exercise. In the final phase, we compared contractile properties of the heart muscle over the first year of life in rats. We concluded from these findings that many of the previously observed changes in systolic function associated with aging, occur between 12 and 21-33 months of age, while early signs of increased diastolic stiffness manifest sooner.

Overall, though more work is required, this thesis presents evidence that structural and mechanical properties of the heart are adaptable and can be modified by either positive (exercise and diet) or negative (obesity and aging) factors.