Dietary Nitrate Supplementation: Dose Response Relationships and Effects on Intermittent Exercise Performance
Dietary supplementation with inorganic nitrate (NO3 has been shown to lower the oxygen (O2) cost of submaximal exercise and to improve performance during continuous endurance exercise. The objectives of this thesis were: 1) to improve understanding of the supplementation procedures in which NO3 is most likely to benefit exercise physiology and performance, and 2) to explore the ergogenic potential of dietary NO3 in intermittent exercise. Recreationally active adult participants volunteered to participate in the original investigations presented in this thesis. These participants underwent various oral NO3 supplementation regimes and subsequently provided venous blood samples for the determination of plasma nitrate concentration [NO3 and plasma nitrite concentration [NO2 and completed different exercise tests to assess the potential for NO3 supplementation to improve physiological responses during exercise and exercise performance. Chapter 4: Following the ingestion of 70, 140 and 280 mL concentrated NO3 rich beetroot juice (BR: containing 4.2, 8.4 and 16.8 mmol NO3 respectively) plasma [NO2 increased dose dependently, with peak changes occurring at ~2 3 h post ingestion. The O2 cost of submaximal exercise and exercise tolerance were also influenced dose dependently 2.5 h post acute BR ingestion when compared to a NO3 depleted placebo (PL) Specifically, 8.4 mmol and 16.8 mmol lowered the O2 cost of moderate intensity exercise by 1.7% (P 0.06) and 3.0% (P 0.05) respectively. Exercise tolerance during severe intensity exercise was significantly improved after ingestion of 8.4 mmol +14% P 0.05) with no further improvement evident following ingestion of 16.8 mmol +12% P 0.05) 4.2 mmol NO3 did not significantly lower the O2 cost of submaximal exercise or improve exercise tolerance. Chapter 5: Plasma [NO2 was dose dependently elevated 2 h and after 7 days and ~4 weeks of supplementation with 3 mmol and 6 mmol NO3 Compared to pre supplementation baseline, and PL, moderate intensity exercise O2 uptake O2) was not lowered with a low dose of dietary NO3 (3 mmol NO3 acutely (2 h) or after ingesting it daily up to ~4 weeks. In contrast, ingestion of 6 mmol NO3 significantly lowered submaximal exercise O2 by 3% after 2 h (P 0.06) 7 days and ~4 weeks (both P 0.05) of supplementation. Another interesting observation was that the reduction in submaximal exercise O2 after ~4 weeks of supplementation with 6 mmol NO3 was preserved 24 h after consumption of the final NO3 dose despite plasma [NO2 having returned to baseline. Chapter 6: In recreational team sport players, 28 mmol dietary NO3 administered over ~30 h improved performance in the Yo Yo