No improvement in endurance performance after a single dose of beetroot juice


Journal Title (Medline/Pubmed accepted abbreviation): Int. J. Sport Nutr. Exerc. Metab.
Year: 2012
Volume: 22
Page Numbers: 470-478
doi:

Summary of background and research design:
Background: Consumption of beetroot juice is gaining popularity in many athletic competitions. Due to its high amount of nitrate, beetroot juice is able to improve oxygen delivery to the muscles and improve exercise tolerance.

Hypothesis: Like larger volumes of beetroot juice, a 140-mL dose of concentrated beetroot juice will improve performance on a cycling time trial lasting about 1 hour in experienced cyclists.

Experimental Design: randomized, double-blind, crossover study

Subjects: Trained, male cyclists or triathletes (n = 20), age 26 ± 1 y

Treatments: Concentrated beetroot juice: 140 mL juice containing 98% beetroot juice and 2% concentrated lemon juice. One serving contained 8.72 mmol nitrate (~540 mg).
Placebo- the same juice with the nitrate removed (0.004 mmol nitrate/serving, ~0.25 mg)

Protocol: The participants were first evaluated for maximal workload capacity (Wmax) and maximal oxygen capacity (VO2max) on a stationary bicycle. In a subsequent visit, they were familiarized with the time trial protocol. They then reported to the laboratory twice, visits separated by one week, to perform the time trial with one of the two treatments. They consumed a standardized dinner the night before each trial, and then reported to the laboratory the next morning after an overnight fast. A baseline blood sample was collected, and then the participant consumed one of the two treatments (2.5 hours before the time trial). A standardized breakfast was consumed 15 min later (2.25 hours before the trial). Blood was then sampled every 30 min until the trial. After a 5 min warm-up on the stationary cycle, they were asked to complete 1,073 ± 21 kJ of work (calculated from Wmax so that the trial took about 1 hour). A post-workout blood sample was also collected. Blood was analyzed for nitrate, nitrite, glucose, insulin, lactose, and free fatty acid concentrations.

Summary of research findings:
  • In 120 min, plasma nitrate concentration increased from 37.7 ± 2.7 μM to 310 ± 5.3 μM with the beetroot juice and did not increase at all with the placebo. Nitrite, a metabolite of nitrate, increased about 2-fold with beetroot juice and not at all with the placebo.
  • Plasma concentrations of glucose, lactate, insulin, or free fatty acid did not differ between trials.
  • With beetroot juice, it took the participants 65.5 ± 1.1 min to complete the time trial. With the placebo, it took 65.0 ± 1.1 min. These results are not statistically different.

Key practice applications: A concentrated beetroot juice supplement containing 8.7 mmol nitrate did not improve performance on a time trail lasting about 1 hour long. The ability of beetroot juice to have a beneficial effect on exercise may be related to the duration and/or intensity of the exercise. A recent study reported benefits on a cycling trial that lasted 6-30 min. Therefore, beetroot juice/nitrate supplementation may be more beneficial in short duration exercise.
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