Dietary antioxidants and the efficiency of oxygen transport and uptake during endurance exercise : a thesis submitted for the degree of Doctor of Philosophy, School of Sport and Exercise, College of Health, Massey University
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2018
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Massey University
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Abstract
This thesis aimed to determine whether various dietary antioxidant supplementation protocols could enhance the efficiency of oxygen (O2) transport during endurance cycling, and subsequently improve exercise performance. Two naturally-sourced supplements (keratin; KER and pomegranate extract; POMx) were selected for investigation, based on their rich content of either thiols (KER) or polyphenols (POMx).
Study One was a crossover study which compared the effect of chronic KER intake compared to a sodium caseinate placebo (CAS) of equal protein content. Fifteen endurance-trained males consumed the supplement on six days per week, for a period of four weeks (0.8 g.kg-1d-1), while participating in endurance cycling training. Blood samples collected throughout each intervention period were unchanged by either supplement for any parameter measured (all p > 0.05). Likewise, neither the O2 consumption (VO2) required to sustain a given level of submaximal cycling exercise, nor the maximal VO2 attained during a graded exercise test to exhaustion were affected by KER or CAS (submaximal VO2, p = 0.13; VO2max, p = 0.25). Further, the maximal power output obtained in the VO2max test was not significantly different between treatments (p = 0.51). Consequently, KER was not recommended as an ergogenic aid for athletes.
Study Two investigated the effects of acute POMx supplementation on VO2 during submaximal and maximal cycling exercise, in normoxic (sea-level; SEA) and hypoxic (1657m altitude; ALT) environments. In a randomized, double-blinded, crossover study design, eight highly-trained cyclists ingested 1000 mg of POMx or a placebo (PLAC), 2.5 hours prior to completing three stages of submaximal cycling at 50%, 65% and 80% of maximal O2 consumption (VO2max), followed by a time trial to exhaustion at a workload calculated to elicit 100%VO2max (TTE100%). The protocol was completed on four occasions: in SEA and ALT, with a POMx, and a PLAC trial in each environment. POMx did not alter VO2 during submaximal exercise in either environment (p = 0.67), or during the TTE100% in SEA (p = 0.46). However, its intake allowed maintenance of SEA VO2 values during intense exercise in hypoxic conditions, as indicated by the VO2 measured five minutes into the TTE100% (+3.8 ml.min-1kg-1, 95% CI, -5.7, 9.5, p = 0.001). However, despite this, POMx did not significantly affect TTE100% performance in either environment (p = 0.41), possibly due to the highly-trained nature of participants, who may have required a longer supplementation period for an ergogenic effect to be observed with POMx.
Study Three was based on the above findings, and aimed to determine whether an 8-day supplementation period with POMx would be sufficient to alter VO2 and cycling performance at sea-level. Further, this study explored the benefits of combining thiol and polyphenol antioxidants to take advantage of their theoretically complementary effects on erythrocytes and nitric oxide (NO). Eight trained cyclists completed four supplementation protocols in a randomized, blinded, crossover designed study: placebo (stevia, PLAC), POMx only, N-acetylcysteine (NAC) only and POMx + NAC (BOTH) for eight days (15 mg.kg-1d-1). On the eighth day, 2.5 hours after the final dose, the participants completed a submaximal cycling protocol, as described for Study Two, followed by a five-minute time trial. As opposed to the acute supplementation protocol in the previous study, short-term POMx supplementation decreased the VO2 required to complete each stage of the submaximal part of the exercise test compared to all other supplement conditions (-2.1 ml.min-1kg-1, 95% CI, -2.8, -0.23, p < 0.04). In contrast, NAC significantly increased submaximal VO2 (+1.9 ml.min-1kg-1, 95% CI, 0.26, 3.6, p < 0.03), negating the POMx-lowering effects on POMx when the two were co-supplemented. Regardless, none of the treatments significantly
altered performance in the subsequent time trial (p > 0.05). Thus, it is suggested that this test was too short for the increased VO2 efficiency to show any meaningful effects on performance.
In conclusion, based on the lack of evidence for enhancement of performance, this thesis does not support the recommendation of the selected dietary antioxidant supplements for athletes, for performance-enhancing effects at least. However, because the primary outcome measure of this thesis, VO2, appears to be altered by POMx, the intake of polyphenol-rich products warrants further investigation. Based on the results of Chapters 6 and 7, it appears that the benefits of POMx become more significant as demands on O2 transport and utilization processes increase. Therefore, the suggested areas of future research would involve exercise of greater duration, and environmental conditions where O2 availability and/or limitations to the various transport parameters differ.
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Content removed from thesis for copyright reasons: Crum, E.M., O'Connor, W.J., Van Loo, L., Valckx, M., & Stannard, S.R. (2017). Validity and reliability of the Moxy oxygen monitor during incremental cycling exercise. European Journal of Sport Science, 17(8), 1037-1043
Keywords
Antioxidants, Oxygen, Physiological transport, Endurance sports, Physiological aspects, Athletes, Nutrition, Research Subject Categories::INTERDISCIPLINARY RESEARCH AREAS::Sports