Role of the Cardiovascular System and the Brain in Determining Individual Tolerance to Exercise

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How easy exercise feels for an individual can determine their willingness to participate in physical activity (tolerance for exercise). Being physically active is an important part of quality of life for Canadians. Understanding what contributes to an individual's exercise tolerance is therefore important to establish. It is known that when a person exercises in environments where there is a reduced amount of oxygen, such as at altitude, exercise feels more difficult. This is explained by the fact that the supply of oxygen provided to muscle during exercise can determine how well the muscle functions. This supply depends on the small blood vessels inside exercising muscle widening to allow more blood flow, and the heart increasing its output of blood to the body.****The current view is that if you are a young and healthy adult in normal oxygen environments your oxygen delivery is tightly matched to the demands of the exercising muscles and therefore is not determining your exercise tolerance. This view is based on research studies where the average response of a group is used to understand how this matching works when a person is exercising. However, in my laboratory we have recently discovered that a healthy young individual's heart and blood vessel response might be inherently better or worse than another's at this matching. Not only that, but this might actually be a reason why one person feels a certain amount of exercise as more difficult than another person. However there is currently a very poor understanding of this individual difference phenomenon. Therefore, the specific objectives of this proposal I and my HQP will pursue are to A) Establish the existence of individual differences in exercising muscle blood vessel and heart responses to sustainable exercise, B) Demonstrate that these differences are closely linked to the oxygen levels in the muscle, C) Demonstrate that they contribute to exercise tolerance differences between individuals, D) Identify what mechanisms are different across individuals that explain this.***Another possible contributor to how difficult (or not) exercise feels is how the brain senses the exertion of exercise. Research into which areas of the brain are involved in the perception of exertion and how this perception can be modified is only really beginning. A big problem for researchers has been that the best technique to monitor activity of the brain and identify how much and where this activity is (magnetic resonance imaging (MRI)) requires the head to be very still. This has required researchers to look at the brain immediately after, rather than during, exercise. We are developing a way of exercising that will overcome this problem. With this approach I and my HQP will pursue these specific objectives A) Map the brain responses during exercise that are related to perception of effort and B) Identify how the brain responses change when perceived exertion is made to increase or decrease.******