Neural and muscular aspects of fatigue and long-term acclimatization to high altitude.

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My program of research involves the use of innovative techniques to advance our understanding of human neuromuscular physiology, with emphasis on the development of fatigue. Fatigue produced by physical activity is a common experience for healthy individuals and it is magnified for many populations (e.g., healthy older adults, patients with cancer, heart disease, chronic lung disease, stroke survivors, etc.) such that the performance of even day-to-day tasks can be limited. Importantly, the development of fatigue is dependent not only on the conditions of the task but also factors such as the sex and age of the participant. It is a long-term objective of my research program to identify the physiological mechanisms of fatigue and to use this knowledge to develop interventions that will help to reduce the impact of fatigue on the lives of Canadians. This research proposal includes three themes of experiments designed to increase our understanding of the mechanisms of fatigue. In the first theme, multiple stimulation techniques (magnetic stimulation of the brain as well as electric stimulation of the spinal cord and peripheral nerve) will be used during voluntary contractions to examine mechanisms of fatigue within the central nervous system (central fatigue). There is evidence that more than 50% of force loss with fatigue can be caused by changes in the brain and spinal cord so it is imperative to identify these mechanisms and also determine if there are differences between females and males. In theme two, fatigue will be induced by applying stimulation over a muscle to cause contraction without input from the nervous system and thereby allow insight into mechanisms of fatigue within the muscle (peripheral fatigue) for females and males. These electrically-evoked contractions are an important means to maintain muscle mass or restore motor function for individuals with limited exercise capacity (e.g., a stroke survivor) but lead to rapid force loss so it is important to find the optimal stimulation parameters to minimize fatigue. The last theme of experiments is dedicated to understanding the role that reduced oxygen availability has on fatigue. To do this, people who reside close to sea level will travel to high altitude and complete voluntary and electrically-evoked protocols to assess central and peripheral fatigability with acute exposure to hypoxia and during acclimatization. Establishing the relationship between oxygen tension and fatigability is essential to our comprehension of pathologies associated with low levels of oxygen in the blood.