The role of oxidative, inflammatory and neuroendocrinological systems during exercise stress in athletes
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Introduction: Exercise induces a stress reaction that initiates adaptive processes, which can be modified by intensive physical training and / or exogenous antioxidant supplementation. However, the optimal exercise training strategy and corresponding level of antioxidant support for positive adaptation remains unclear. Therefore, the overall aim of this thesis was to investigate the interactions between exercise-induced changes within the oxidative, inflammatory and neuroendocrinological systems and antioxidant supplementation on athletic performance during intensive physical training. Three separate studies were undertaken and reported in four manuscripts. Study 1: In Study 1, well-trained athletes (n = 23) completed a 4 day food record during a period of intensified physical training. Collectively, the participants consumed a sufficient dietary intake of antioxidants (vitamin A, C and E) according to the Australian recommendations. Study 2: Study 2 used a crossover experimental design to examine the effect of intensive physical training on oxidative damage, inflammation, hormonal disturbances and performance capacity. Participants (n = 7) completed a high-intensity intermittent running protocol following both a reduced (LOW) and intensive (HIGH) 4 day physical training period. The results demonstrated that HIGH physical training led to an increased amount of muscle damage, decreases in sprint velocity (P < 0.001) and a reduction in total distance covered (P < 0.05) during the high-intensity intermittent running protocol. HIGH physical training also induced a greater increase in oxidative damage (xanthine oxidase) markers 2 h post-exercise (paper 1). Neuroendocrinological measures (growth and thyroid hormones) were not altered by training-induced fatigue (paper 2). These findings suggest that 4 day HIGH training can impair high-intensity running performance and exacerbate oxidative damage. Study 3: Study 3 used a double blind randomised placebo-controlled crossover design to investigate the effect of 9 d oral N-acetylcysteine (NAC) supplementation (1200 mg/day) in eight well-trained triathletes. Changes in performance (cycle ergometer race simulation) and pre- to post-exercise biochemistry measures were taken to determine the ergogenic effect of NAC and associated reaction within the oxidative and inflammatory systems. It was demonstrated that oral NAC supplementation enhanced repeat sprint cycling performance via an improved redox balance and promoted adaptive processes in well-trained triathletes undergoing intensive physical training. NAC supplementation was also effective at blunting the inflammatory response to exercise. Conclusion: Collectively, this thesis provides novel information regarding the dose-response relationship between training-induced fatigue, antioxidant supplementation and athletic performance.
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