Dietary nitrate supplementation improves rowing performance in well-trained rowers


Journal Title (Medline/Pubmed accepted abbreviation): Int. J. Sport Nutr. Exerc. Metab.
Year: 2012
Volume: 22
Page numbers: 251-256
Summary of background and research design:
Background: Nitric oxide (NO) is a molecule that increases blood flow.  Increased generation of NO by the body during exercise is thought to lead to increased performance since it is possible for increased rate of nutrients to the muscles and removal of waste products from the muscles.  NO is a gas and therefore cannot be ingested directly, but nitrate is converted to NO in the body.  Beetroot juice is an excellent source of nitrates and had not currently been tested in rowers.

Hypothesis:  Consumption of 500 mL beetroot juice for 6 days will improve the performance of elite rowers.

Subjects:  Highly trained junior male rowers (n = 14), age 16.7 ± 0.5 y

Experimental design: randomized, double-blind, placebo-controlled, crossover study

Treatments:
Homemade beetroot juice- 500 mL/day (about 2 cups, 5.5 mmol nitrate /day) divided into 2 × 250 mL servings
Placebo- black-currant juice (negligible nitrate content)

Protocol: Physiological measures were recorded at the commencement of the study including urine specific gravity, pH of the urine, nitrates in the urine, blood pressure, and oxygen saturation in the blood.  Baseline performance was evaluated on a stationary rowing machine.  On 4 separate equations during one month, they completed 6 × 500 m rowing sessions at maximum intensity with 90 seconds rest in between.  Four sessions were completed to assure that baseline assessments were accurate.  The time it took to complete each sprint was measured.  Heart rate and oxygen saturation were measured 0, 1, and 2 min after the exercise sessions; blood was acquired for analysis of lactate concentration; and urine was collected for the measurements as at baseline.  Their coach was there for all sessions.  After baseline testing, the participants were assigned to one of the beverages.  After 6 days of supplementation, the 6 × 500 m test was repeated.  They then had a 1 week washout period and repeated the protocol with the other beverage.
Summary of research findings: 
  • The beetroot juice improved the average time for the participants to complete the sprints, from 90.19 sec to 89.40 sec.  This is equal to a 0.4% benefit (± 1.0%, 95% confidence limit).  In elite rowers, it has been shown that a 0.3% increase in performance can make a difference between first and second place.
  • The benefit was much greater for the latter sprints (1.7 ±1.0% benefit during sprints 4-6 compared to a -1.0 ± 1.7% effect on performance during sprints 1-3).
  • The nitrate concentration in the urine was not different between the legs of the study: 2.50 ± 1.2 mg/dl with beetroot juice vs. 2.43 ± 0.09 with the placebo.  This suggests that a) the nitrates that had been consumed had already been excreted from the system or b) nitrates were accumulating in the system.

Key practice applications: Supplementation with beetroot juice for 6 days increased high-intensity rowing performance, especially sprints that were completed in the later stages of the evaluation

Limitations: Beetroot juice is a whole food-based supplement and therefore it is not known if the nitrates themselves are responsible for the performance benefits.  Other nutrients or combinations of nutrients may indeed be responsible.  However, it should be noted that other studies, using de-nitrated beetroot juice, have shown similar results, suggesting that it is, in fact, the nitrate that is responsible for the observed effects.

Key search terms for this article (5-7 terms): nitrates, nitrites, nitric oxide, blood flow, rowing
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