Friday, June 5, 2015

Nitrate Supplementation Study Supports "Increased Blood Flow ➲ Increased Peformance" Claim From NO-Write-Ups

Does the vasodilatory effect of nitrates have a direct ergogenic effect that correlates with increases in blood flow?
If you are someone who actually reads the "product write-ups" (=ads) for NO boosters you will have heard the claim that the NO-induced vasodilation and the subsequent increase in blood flow will have significant performance enhancing effects. If you are a critical thinker, you will yet also have noticed that a "[citation]" (=reference) that would prove this claim is missing... with the publication of a recent study from the Université Droit et Santé Lille this may change in future write-ups.

In said study, Julien Aucouturier et al. tried to determine whether 3 days on NO3-rich beetroot juice would boost the tolerance to supra-maximal intermittent exercise.
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To this ends, the French researchers had their subjects, who were not previously engaged in any form of intense endurance exercise perform a standardized exercise test, which consisted of 15-second exercise periods at 170% of the maximal aerobic power interspersed with 30-second passive recovery
periods, to failure.
Figure 1: Overview of the study design (Aucouturier. 2015).
All subjects performed the standardized testing procedure twice - at the same time of the day, but seperated by at least one, maximally two weeks. Once without after ingesting 680mg of NO3- for three days from beetroot juice, once after ingesting the low nitrate (<5mg/L) apple-black currant juice that was used as a placebo.
Figure 2: Individual data points for the increase in reps (=number of intervals to exhaustion) and markers of potential mechanisms that trigger this increase, i.e. ventilation (right, top) & oxygen uptake (right, bottom | Aucouturier. 2015)
The individual data points in Figure 2 (which are much more meaningful than group averages) show that the majority of the subjects experienced a measurable, some of them even a significant increase in exercise tolerance in response to the ingestion of 680mg of NO3- from beetroot juice over a three-day period.

Before we get back to the mechanism I hinted at in the introduction, already, I want to highlight one last thing that follows from the previously highlighted result: If "only" more than 50% of the subjects benefited from the NO3- almost 50% of them didn't benefit and that's not exactly news when it comes to beetroot juice and nitrate supplementation. Previous studies showed similarly conflicting results with some suggesting that the training status of the subjects may be a significant modifier (athletes may benefit less than couch potatoes), but the reason for the differentials response of the subjects is something to investigate in another study.
So what's the news and link to NO boosters, here? What is really interesting, about the study is not the performance increase. That's no news. What is news, though, is the potential mechanism.

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If we take a look at the data that is available it is obvious that the increase in exercise performance was not mediated by improvements in contractile function (maximal voluntary force during an isometric leg extensor exercise was not modified by NO3- supplementation) or resting hemodynamic parameters, which are the "usual suspects" when it comes to NO3-induced performance increases. Rather than that, the only difference that may explain the performance increase is surprisingly the previously mentioned increase in blood flow or, more specifically, the increase in microvascular total hemoglobin in the vastus lateralis muscle which was assessed by near infrared spectroscopy and increased by 18% (BJ: 9662±1228a.u. vs. placebo:8178±1589 a.u.; P<0.05).

That's not yet "prove" that it's a simple increase in blood flow that triggers the performance increase, though. After all, the scientists could simply have missed to measure another, hitherto unknown factor that triggers the performance increase,... but alas! In the end, it matters that more than 50% of the subjects saw performance increases, right? | Comment on Facebook!
  • Aucouturier, Julien, et al. "Effect of dietary nitrate supplementation on tolerance to supramaximal intensity intermittent exercise." Nitric Oxide (2015).