Effects of Endurance Exercise on Cerebral and Muscle Oxygenation

Abstract

It has been suggested that during exhaustive exercise both a central and peripheral mechanism of fatigue exists. Indeed, a central debate in the exercise science literature is the nature of fatigue that determines exercise performance under different conditions (Swart et al., 2009a). Hypoxia, for example, has a small but direct role on the cessation of exercise, specifically during endurance performances (Millet, Aubert, Favier, Busso, & Benoit, 2008; Secher, Seifert, & Van Lieshout, 2008). Numerous studies to date have provided new information related to the factors implicated in short-term high intensity exercise, while more studies of a longer nature (endurance time trials), measuring central and peripheral fatigue factors simultaneously, and under hypoxic conditions, are needed to add additional information to guide our understanding of the mechanisms involved in central and peripheral fatigue. This thesis represents a contribution to the much needed research within this area. Four key papers, separated into four chapters, discuss this research in this thesis. To investigate these effects, an integrative physiological approach was used by including muscle and cerebral oxygenation changes (NIRS), cardiovascular and pulmonary responses and blood biochemistry during cycling exercise in a normoxic and hypoxic environment. The primary inference of this thesis is that in hypoxia the brain is protected and the muscle is in need of a similar oxygenation and extraction to do less work; a finding that contributes to the support of previous speculations in the literature. A secondary inference of this thesis is that a difference in the pattern of oxygenation between continuous and incremental exercise exists; a finding that has not been previously identified in the literature. The findings from this study have therefore furthered our understanding of the nature of fatigue, specifically in endurance exercise under acute hypoxic conditions, and the relationship between the central and peripheral factors associated with fatigue.