Nitrate supplementation’s improvement of 10–km time–trial performance in trained cyclists
 
 
Journal Title (Medline/Pubmed accepted abbreviation):  Int. J. Sport Nutr. Exerc. Metab.
Year: 2012
Volume: 22
Page numbers: 64-71

Summary of background and research design:

Background: Nitric oxide (NO) is a compound that increases blood flow and improves muscle contractibility, among other biological effects that could benefit athletes. Dietary nitrate and nitrite can be converted to NO within the body. Specifically, it has been shown that 0.5 L (about 2 cups) of beetroot juice, which is high in nitrate, per day for 6 days reduces the oxygen requirement during exercise, implying more efficient use of oxygen.

Hypothesis: Consumption of 0.14 L (about 2/3 cup) of concentrated beetroot juice for 6 days will improve performance on a 10–km cycling time trial.

Subjects: Twelve male cyclists or triathletes, age 31 ± 3 y completed the study

Experimental Design: randomized, double–blind, cross–over, placebo–controlled

Treatments: Concentrated beetroot juice that contained about 8 mmol nitrite per day or a placebo: nitrate–depleted concentrated beetroot juice (140 mL, or about 2/3 cup)

Protocol: Before the study, the participants were familiarized with the procedures and were evaluated for VO2max. For 6 days the participants consumed one of the treatments after breakfast. On the 6th day, the participants completed a cycling time trial (2.5 hrs after the standardized breakfast and supplement). A resting blood pressure measurement and baseline blood samples were acquired, and then the participants cycled at 45% of their previously determined maximal work output (Wmax) for 30 min then 65% Wmax for 30 min. Gas exchange (oxygen and carbon dioxide) heart rate, and perceived level of exertion were monitored at defined intervals throughout the ride, and blood samples were acquired. After the 60 min ride, participants completed a simulated 10 km time trial at maximum effort where only time was noted. At least 14 days later, the participants repeated the experiment with the other treatment. Plasma was analyzed for nitrite, glucose, insulin, lactate, and free fatty acids.


Summary of research findings:
  • Consumption of beetroot juice resulted in lower amount of oxygen consumption (VO2) at both 45 and 60% Wmax, suggesting more efficient use of oxygen.
  • There was no difference observed in VCO2, heart rate, respiratory exchange ratio, or perceived exertion.
  • Although carbohydrate oxidation rates appeared similar between treatments, there appeared to be a slightly lower rate of fat oxidation with the beetroot juice.
  • However, there was a greater amount of free fatty acids in the blood immediately after exercise, indicating a greater amount of fat mobilization. (This discrepancy was not addressed).
  • Beetroot juice was associated with a 12–second faster time trial compared to the placebo (P < 0.05).

Key practice applications: : Consumption of concentrated beetroot juice for 6 days has the ability to enhance performance, possibly by improving the efficiency of oxygen utilization.

Key search terms for this article (5-7 terms):nitrate, nitrite, nitric oxide, beetroot, beet root, endurance, cycling

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