Influence of acute dietary nitrate supplementation on 50 mile time trial performance in well-trained cyclists


Journal Title (Medline/Pubmed accepted abbreviation): Eur. J. Appl. Physiol.
Year: 2012
Issue: 20 April
doi: 10.1007/s00421-012-2397-6
 

Summary of Background and Research Design

Background: Nitric oxide (NO) is a natural molecule that increases blood flow and is thought to aid in sports performance by delivering nutrients to muscles and removing waste products at a faster rate.  Beetroot juice is high in nitrate, which is converted to NO in the body.  Beetroot juice has been shown to increase performance in short cycling races (about 2-10 miles).  Elite athletes have been shown to exhibit a greater baseline concentration of nitrate in the blood, and greater ability to synthesize NO, and it is unknown if beetroot juice will have the same effect on elite athletes performing longer races.

Hypothesis: Beetroot juice will improve performance for elite cyclists during a 50 time trial.

Subjects: Eight male competitive cyclists, age 31 ± 11 y, who trained 11.1 ± 2.5 hrs per week

Experimental design: randomized, double-blinded, placebo-controlled, cross-over trial

Treatments : 500 mL of beetroot juice (about 6.2 mmol nitrate) or nitrogen-depleted beetroot juice (about 0.0047 mmol of nitrate).

Protocol : Initially, the participants were familiarized with the equipment and the protocol and their VO2max was measured.  The time trial occurred indoors on their own bicycles mounted on a trainer system.  They arrived at the laboratory after not eating for at least 1 hour.  First, blood pressure was measured and a blood sample was collected for analysis of nitrate concentration.  Then, they consumed one of the test beverages.  Two hours later, their blood pressure was measured again and exactly 2.5 hrs after ingestion they began a 50 mile time trial.  Power output and gas exchange were monitored throughout the ride.  Every 10 miles, a finger-stick blood sample was acquired for measurement of blood lactate concentration.  The participants were allowed to consume sports beverages and/or snacks at will during the first ride, and the routine was repeated at the second ride.  Water was provided thoughout.  At least one week later the participants returned for a second time trial with the other beverage.
 

Summary of Research Findings
  • Beetroot juice supplementation increased nitrate concentration in the blood an average of 30%, from about 389 ± 107 nM to 472 ± 96 nM.
  • With beetroot juice, the participants rode faster than without beetroot juice, but the difference did not reach statistical significance (beetroot juice: 136.7 ± 5.6 min, nitrate-depleted beetroot juice: 137.9 ± 6.4 min, p > 0.05).
  • Analysis of the speed ran during the different segments of the time trial revealed that those who consumed beetroot juice ran faster during the last 10 miles than those who had the placebo (p < 0.05).
  • A correlation was seen in between the increase in nitrate concentration and time trial time (r = -0.81, p < 0.05).
  • There were three participants whose plasma nitrate concentration increased less than 10% with beetroot juice (“non-responders”); these participants performed similarly during both trials.
  • When only “responders” were considered, power output during the trial was significantly higher with beetroot juice compared to the placebo (p < 0.05).

Key practice applications

The most interesting finding in this study was that 3 of the 8 participants’ blood nitrate concentration did not increase after beetroot juice consumption, and these participants did not experience any gains from the supplement during their run.  In contrast, the other 5 participants’ blood nitrate concentrations increased >30%, and performance increased >0.8%, where the smallest “worthwhile change” is estimated to be 0.6%.  It is unknown why some participants were “responders” and some were non-responders”, but it may have to do with their habitual diet.
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