The effects of repeated bouts of prolonged cycling and carbohydrate supplementation on immunoendocrine responses in man
Prolonged strenuous exercise affects the circulating numbers and functions of immune cells. These effects are thought to be largely mediated by the actions of elevated circulating stress hormones and alterations in regulatory cytokines. Although the effects of a single acute bout of exercise on immune system function are quite well established, it is still not clear how time of day and repeated bouts of prolonged exercise on the same day influence immune function. It is of particular interest to understand the effects of nutritional supplementation on immunoendocrine responses. Therefore, the aims of the studies described in this thesis were to determine the effects of two bouts of prolonged cycling and carbohydrate supplementation on immunoendocrine responses. The saliva collection study showed that the use of a swab for collecting saliva is not an ideal method because it affects the results of saliva composition (Chapter 4). The comparison of the effects of exercise at different times of day on immunoendocrine responses showed that a single bout of prolonged exercise performed in the afternoon induces a larger perturbation in the redistribution of leukocytes into the circulation than an identical bout of morning exercise, which maybe due to higher hypothalamic-pituitaryadrenal (HP A) activation and. circadian rhythms. However, in terms of oral mucosal immunity, performing prolonged cycling at different times of day does not differently affect the salivary responses. The second compared with the first of two bouts of prolonged exercise on the same day induces a greater HP A activation, a larger leukocyte trafficking into the circulation, a decreased neutrophil degranulation response to lipopolysaccharide (LPS) on per cell basis and a lower saliva flow rate, but does not increase plasma interleukin-6 (IL-6), or change saliva immunoglobulin A (slgA) secretion rate (Chapter 5). Furthermore, carbohydrate (CHO) ingestion during any period of two bouts of prolonged exercise shows limited beneficial effect in blunting these higher responses in the second exercise bout compared with the first identical exercise bout on the same day (Chapter 6, 7 and 8). The determination of the effects of CHO ingestion on exercise-induced immunoendocrine responses showed that when two bouts of exercise are performed on the same day, the greater benefit in terms of circulating immunoendocrine responses is obtained by feeding CHO at the earliest opportunity (Chapter 6, 7 and 8). A 3-h interval is insufficient for recovery of leukocyte mobilisation and neutrophil function from the impact of previous exercise whether subjects consumed placebo or CHO during exercise or recovery (Chapter 5, 6, 7 and 8). However, an 18-h interval is sufficient for full recovery of all immunoendocrine variables that were measured in this thesis from the impact of two bouts of prolonged exercise (Chapter 8).