Nitrates Work! Even at Low Doses of 300-500mg. Athletes Who Take More or Confuse Nitrates With Nitrites Face Potential Health Risks. First NO2-"Victim" in the ER.

Image 1: With nitrate and nitrite, a
single letter is of literally vital importance.

You probably expected another issue of the famous "Ask Dr. Andro" segment today... ? Well, I have in fact been working on something, but firstly, the topic turned out to be so epic that I could hardly have delivered a post in the usual SuppVersity quality within the next few hours, and secondly, a previous installment of the series on creatine nitrate (cf. Ask Dr. Andro: Is Creatine Nitrate Worth It?), in which I explained why I think that the heavily marketed "revolutionary" creatine supplement probably does not provide any additional benefits beyond supplementing creatine monohydrate and nitrate, individually, urgently needed a follow up.

While the ergogenic potential of creatine monohydrate and its safety are well established (and I do not think I have to recite the whole litany about creatine causing kidney failure, again!? cf. Creatine Save - For Diabetics, As Well!), the studies which show that dietary supplementation with inorganic nitrate (NO3-) reduces whole body oxygen cost during physical exercise (Larson. 2007; Larson. 2010), are pretty recent and have, according to a letter to the editor of the Journal of Applied Physiology by Jon O. Lundberg et al. (Lundberg. 2011), already provoked a case of severe nitrite intoxication in an athlete who obviously wasn't aware of the major difference the "i" which distinguishes the highly reactive nitrite (NO2-) from its harmless precursor nitrate (NO3-) and developed symptoms suggestive of methemoglobinemia (increased oxidation of hemoglobin) after poisoning himself with nitrite salt.

Note! It is unlikely that you will develop methemoglobinemia from reasonable doses of nitrate, even when the lethal dose 50 (LD50 = the dose at which 50% of the subjects / lab rats who ingested the given amount of a chemical die) for nitrite is as low as 100-200mg/kg and thus in the range of cyanide. The reason for that is that, although your body will convert orally ingested nitrates to nitrite, the rate at which this process takes place is limited and this limitation is what avoids the accumulation of nitrite in your blood stream and thus saves the iron-containing oxygen-transport metalloprotein in your red blood cells from being oxidized.

Image 2: Beetroot juice is probably your
safest source of dietary nitrate (NO3-)
(image from planetorganic.com)

This case of unintentional nitrite poisoning goes to show that caution should be exercised, when you are buying and consuming nitrate salts for performance issues. Yet, although salpeter (nitrate salt) is readily available as a food conservative from your local grocery story, I personally would advice against its consumption and tend towards more natural sources of nitrate to elicit the desired ergogenic effects. In fact, the slow controlled release of nitrite from dietary nitrate as it is found in beat root juice (100-200ml would suffice to get into the effective range of 200-300mg nitrate, cf. Ask Dr. Andro: Is Creatine Nitrate Worth It?) may have additional desirable health effects on blood pressure (Larsson. 2006; Lundberg. 2008) and could be used as an adjunct in the treatment and prevention of ischemic conditions such as myocardial infarction and peripheral artery disease.

A final word of caution goes out to the real bros out there: When even nitrite salt can give you hypothension and oxidize your the oxigen carrying metalloprotein in your red blood cells, nitroglycerine and amyl nitrite, both drugs that are prescribed to patients with heart disease, may literally give you the "longest lasting pump of your life" - a pump that lasts until you drop dead to the floor.

High School Athletes on Dope? Not Really, But Roughly 1/3 Uses "Performance Enhancing Supplements"

"Don't you take those steroids!" Does this remind you of your mother, when, back in high school, you bought your first tub of creatine monohydrate? Recent doping "scandals" have, yet again, raised the awareness, or should I say panicky fear of parents and coaches that their children and wards are going to be delinquent, when they save their allowances for a shopping spree at the local GNC. Accordingly, many of them will not be happy to hear that a recent study published in the Journal of Strength & Conditioning Research (Piattolly. 2011) found that "[a]lmost a third [32.2%] of the high school sample surveyed reported using nutritional or performance enhancement supplements."

Figure 1: Type of performance enhancing supplement used by high school athletes (data adapted from Piattolly. 2011)

Interestingly, of those 32.2% of the young athletes that reported using supplements, the majority were male (87%) and in the age group of 15-17 year-olds. Prevalent sports were baseball (17.8%), football (32.7%), and track and field (22.3%) and the most popular supplements were protein shakes, multivitamins, NO2 boosters and creatine (cf. figure 1), of which more than 50% of the respondent used two or more in combination.

An interesting secondary finding of the study relates to gender differences and the afore mentioned role of parents in their children's choice and consumption of performance enhancing supplements:

When gender comparisons were made, significant t-tests demonstrated that young women rated higher on taking supplements to improve strength, increase size, decrease body fat (p < 0.05) to become a better athlete, and increase physique. With the exception of decrease body fat, all p-values were < 0.001. Significantly more young women reported learning about the supplement from a teammate or friend (p < 0.05), while young men reported learning about the supplement from their parents (p < 0.05).

It is, however, unsettling to know that other than the 25% of the athletes who "said they would consult a nutritionist or physician (25%)" to make sure they chose the right supplements, 26% of the young athletes conceded that "they would take a supplement that could harm their health if they could receive a scholarship".

In view of this last-mentioned result, the fears and anxieties of parents appear in a very different light. Banning or restricting the consumption of harmless supplements like protein shakes will yet hardly solve a dilemma that is rooted much more deeply within a scholarship system where athletic and lately cognitive performance is so tightly bound to the future prospects of adolescents that "doping" muscle and/or brain are on the verge of becoming the norm rather than the exception.

The Beat Your Personal Bests W/ Beets 101: How Much? 8.4 mmol Nitrate ~400-1300g Beets! When? 2.5h Pre Workout!

There are two things you have to keep in mind, when you want to reap the benefits: Timing and dosage. With the currently available nitrate-based / -containing supplements, and both were probably off for the average customer.

It has gotten quiet around nitrate supplements. Irrespective of a handful of interesting studies that were published in the past months (Hoon. 2013; Thompson. 2013), the negative results got more attention among the disappointed consumers of one of the profoundly underdosed nitrate supplements that have suffocated the initial enthusiasm on part of the average and extraordinary gym rat.

The use of the natural alternative, i.e. beet root juice, on the other hand, is complicated, because there is little information on how much nitrate you need and how much of it can be found in the average beet from the supermarket.

Nitrates for your heart: I know ergogenics are sexy, but how sexy is an increase in performance for someone who suffers from regular age- or self-induced lifestyle-related increases in large elastic artery stiffness and endothelial dysfunction? Against that background it's good to know that a group of researchers from the University of Colorado Boulder conclude in their review of the literature that "inorganic nitrite, as well as dietary nitrate, supplementation represents a promising therapy for treatment of arterial aging and prevention of age-associated CVD in humans." (Sindler. 2014)

Luckily Lee J. Wiley et al. must have realized that as well and set out to characterize the plasma NO3 and NO2 pharmacokinetics and the changes in BP after ingestion of three different quantities of NO3-rich beet root juices, as well as the corresponding dose-response relationship between beet root juice and NO3 intake and the physiological responses to exercise. To this ends, the researchers administered different amounts of a beet root concentrate, i.e.4.2, 8.4, and 16.8 mmol from 70, 140, and 280 ml of Beet It, and measure the plasma NO3 and NO2 response, and the blood pressure (BP) of their 10 healthy, recreationally active volunteers (23 yr, height 1.79m, weight 79kg) over a 24h period.

Figure 1: Average plasma NO3 and NO2 levels in healthy male volunteers after the consumption of different amounts of beet root juice concentrate (Wiley. 2014)

As you can see in Figure 1, the effects were dose-dependent and, with respect to the change (not the absolute values) in peak and average NO3 & NO2 levels, almost linear. A similar linearity was not observed for the systolic blood pressure levels which dropped (luckily) not significantly more in response to the ingestion of 16.8 vs. 8.4mmol of nitrate.

Figure 2: The profound drop in systolic BP could be a problem if your BP is already low ➲ dizziness and -worst case- blackout!

"[...S]ignificant main effects by dose and time and an interaction effect on systolic BP (all p < 0.05). [...] The peak reduction in systolic BP occurred 4 h postadministration of 4.2 (5  mmHg), 8.4 (10 mmHg), and 16.8 mmol NO3 (9 mmHg), respectively, relative to baseline (all p < 0.05). Systolic BP was reduced relative to baseline, CON, and 4.2 mmol NO3, at 2, 4, and 8 h postadministration of 8.4 mmol and 16.8 mmol NO 3 (all p < 0.05). There were no differences in systolic BP between 8.4 and 16.8 mmol NO 3 at any time point ( p < 0.05)." (Wiley. 2014)

In that it's certainly remarkable that these effects lasted for 24h, so that the systolic blood pressure was still significantly lower (by 5 mmHg) than at baseline when the scientists took the last reading.

Low blood pressure warning: For the average Westerner it certainly wouldn't be a problem if his blood pressure dropped by 10mmHg, but for a trained athlete who may already have a relatively low systolic BP, the high 16.8mmol (=280ml Beet It) could be straw that breaks the camels neck, i.e. make you feel as if you would black out (see Figure 2).

A similar effect, albeit not dose-dependent effect was observed for the diastolic blood pressure, which dropped significantly, relative to baseline and CON (all p < 0.05). As the researchers point out, the peak reduction in diastolic BP from baseline occurred at 4 h postadministration of 8.4 mmol NO3 (3 3 mmHg) and 2 h postadministration of 16.8 mmol NO3 (4 4 mmHg; both p< 0.05) relative to baseline (both p < 0.05) and returned to near-baseline values by 24 h (p < 0.05).

"What about the really important stuff?"

Oh yes, I almost forgot the effects the scientists observed, when the subjects consumed the beetroot juice 2.5h before a "moderate- and severe-intensity exercise" in the form of a "step" exercise test (20W ➲ 93W ➲ 258W) on a cycle ergometer.

Figure 2: Increase in time to exhaustion (="task failure) during incremental exercise test and average nitrate content (g/100g; based on Wiley. 2013) of beets depending on fertilizer use; the values on top indicate the amount of beets you would have to consume to get to the 8.4mmol nitrate threshold (based on Lee. 1971)

As you can see in Figure 2, these effects, here an increase in the time to exhaustion / "task failure" were not - as the more helps more logic would suggest - most pronounced after the ingestion of the maximal dosage of 16.8mmol of nitrate.

That's good for you, because as you can see on the right hand side of Figure 2, you do already have to consume more 1.3kg of unfertilized beet roots to get up to the medium and most effective dosage of 8.2mmol of nitrate.

Juicin' allowed: You know that I strongly advice against turning your fruits and veggies into an indistinguishable mush, but for beet roots it's probably necessary. Otherwise the nitrate peak will either be postponed or non- existent and the effects the researchers ob- served in the study at hand will be blunted or won't occur at all.

Bottom line: The study at hand confirms that the assumption that more helps more rarely applies, when the thing you could take / have / ingest more of are dietary supplements. Rather than taking more, you should thus make sure to get the timing right - 2.5h before the workout(!), that's when you want to take your nitrate supplements or drink your beet root juice.

In this context, it's worth mentioning that timing, as well as the speed of absorption (see info box to the right) are probably less important, if you are looking for the recently confirmed beneficial effects of nitrite, as well as dietary nitrate, on arterial aging and prevention of age-associated CVD in humans (Sindler. 2014), I discussed in the info-box "Nitrates for your heart".

Reference:

• Hoon, Matthew W., et al. "The Effect of Nitrate Supplementation on Exercise Performance in Healthy Individuals: A Systematic Review and Meta-Analysis." International journal of sport nutrition and exercise metabolism (2013).
• Lee, C. Y., et al. "Nitrate and nitrite nitrogen in fresh, stored and processed table beets and spinach from different levels of field nitrogen fertilisation." Journal of the Science of Food and Agriculture 22.2 (1971): 90-92.
• Sindler, Amy L., et al. "Inorganic Nitrite Supplementation for Healthy Arterial Aging." Journal of applied physiology (Bethesda, Md.: 1985) (2014).
• Thompson, Kevin G., et al. "Influence of dietary nitrate supplementation on physiological and cognitive responses to incremental cycle exercise." Respiratory physiology & neurobiology (2013).

With Beetroot Juice to the SuperBowl XLVIII: 490ml Beetroot Juice Will do the Ergogenic Trick in Team Sports. Plus: Brief Research Overview to Identify Who Else Will Benefit

There are a couple of important confounding factors which will determine whether or not you or anyone else can benefit from nitrate supplementation. Sex is yet - as far as I know know - not one of them... ah, by the way, there may be other benefits to nitrates that are "sex-specific", but in this case the semantics are somewhat different ;-)

You know that the SuppVersity is all about self-education (hence "-versity" as in University), so what would be better than using the publication of the latest paper on the purported ergogonic effects of nitrates as an incentive to "inform" you about the current state of the research? Sounds good? I would think so. Let's take a look, then. What's this nitrate business all about? Contrary to the argument many supplement vendors have been bringing forward to make muscleheads buy their products, the idea is not to use the vasodilating effects for cosmetic pumps that will make you feel - as Arnold said it - better than you felt last night with your significant other (or whom ever else you may have picked up). It's rather their purported effect on the VO2max, which is the maximal oxygen consumption during a workout and the downstream performance effects that puts scientists on -- scientists like Lee J. Wylie and colleagues from the department of Sport and Health Sciences at the University of Exeter, for example (Wylie. 2013).

The latest on dietary nitrate supplementation: Focus on team sport athletes

The paper we are taking a closer look at today has just been published ahead of print in the European Journal of Applied Physiology and investigated the acute effects 490 mL of concentrated, nitrate-rich beetroot juice (BR) and nitrate-depleted placebo juice (PL) had on the performance of fourteen male recreational team-sport players during a Yo–Yo intermittent recovery level 1 test (Yo–Yo IR1) that was performed ~30h after the ingestion of the purported ergogenic (the Yo-Yo IR1 test has been found to mirror the physical demands encountered during team sports, like soccer, football, basketball, rugby etc petty accurately.; cf. Atkins. 2006; Veale. 2010; Vernillo. 2012).

Would dosages as high as in the study at hand (or even higher) provide similar muscle gains, as they were observed with "real" nitrate in rodents (read more).

A note on the "optimal" dosage: The dosage that was used in the study at hand is equal to  ~29 mmol of nitrate, which is 4x more than the current recommended daily allowance in the UK and 6x more than what was most in the majority of previous. Aside from the subjects' training status, which has emerged as a possible confounding factor determining whether athletes will benefit from the consumption of beet-root juice / dietary nitrates, the dosage, as well as the plasma nitrate response (+400% vs. 50-150% in other trials), which was likewise much higher in the Wiley study than in most previous studies, could thus be another important, if not the most important confounding factor. Whether the "more helps more principle" actually holds, whether athletes need more than normalos and if / at which dosages negative side effects occur will yet still have to be elucidated in future trials.

As it was to be expected, the resting plasma nitrite concentration NO2(-) was ~400 % greater in the active compared to the passive trial of this double-blind, randomized cross-over trial (remember: Cross-over means, all participants completed two tests sessions on seperate occasions, one w/ the active, one with the placebo supplement).

Figure 1: Effects of 490ml beetroot juice on serum NO2/3(-) levels, performance and mean glucose concentration during the Yo-Yo R1 test (Wylie. 2013)

As you will learn from the comprehensive research overview further down, the fact that this increase in plasma NO2(-) did also translate into performance increases, on the other hand, was not really to be expected:

Betaine (TMG) increses IGF-1 & lowers cortisol (read more)

"Plasma [NO2 -] declined by 20 % in PL (P\0.05) and by 54 % in BR (P<0.05) from pre-exercise to end-exercise. Performance in the Yo–Yo IR1 was 4.2 % greater (P<0.05) with BR (1,704±304 m) compared to PL (1,636 ±288 m). Blood [lactate] was not different between BR and PL, but the mean blood [glucose] was lower (3.8 ±0.8 vs. 4.2±1.1 mM,P\0.05) and the rise in plasma [K+] tended to be reduced in BR compared to PL (P=0.08)." (Wylie. 2013)

That being said the study at hand confirms that the consumption of a significant bolus of nitrate with all the natural co-factors in beetroot, i.e. >20 betacyanins + derivatives, 11 betaxanthins, highly bioavailable folate, various carotenoids, and, of course betaine has beneficial ergogenic effects on the performance of recreationally active men (Nemzer. 2011). As we are about to see both, the training status of the subjects, as well as the nutrient combination (or absence of the latter) may be a confounding factor due to which this trial was a success whereas ostensibly similar ones were failures.

How does that stuff actually work?

Before we go over to the comparison phase, let's yet briefly check out what the scientists have to say about the underlying mechanism(s) of the ergogenic effects they observed:

• reduction of NO3(-) to NO2(-) and in (sub-)hypoxic or acidic conditions to NO (nitric oxide) - Based on their data, the researchers speculate that this it is likely that this reduction took place during the Yo-Yo  IR1 test (it''s about as likely in most similar high intensity exercise protocols). Base on previous data from Dreissigacker et al. who found signficantly higher baseline NO3(-) and NO2(-) levels in trained vs. untrained subjects an the results of Totzeck et al., who found that baseline NO2(-) correlates with lactate threshold and predicts exercise capacity during an incremental cycle test in highly trained athletes, Wiley and his colleagues argue that it is more than likely that the ability to produce more NO quasi 'on demand' is the underlying cause of the performance increases (Dreissigacker. 2010, Totzeck. 2012).
• dietary nitrate supplementation can protect the phosphocreatine (PCr) stores from being depleted - With PCr being the most readily available energy source for short burst activities like sprinting the preservation of the PCr stores (similar to their "supercharging" via supplemental creatine; click here to learn all about creatine supplementation) would certainly explain why the nitrate supplement delay, what the scientists label as "the attainment of a ‘critical’ intramuscular environment"  and would thus "extend the tolerable duration of high-intensity constant-work-rate exercise". This hyptothesis woul be supporte by the fact that NO increases skeletal muscle glucose uptake, the correspondingly lower blood glucose levels the researchers observed in the active arm of the study and the fact that readily available glucose will spare the PCr stores.
• decreased leakage of K+ (potassium) from the muscle - As the post hoc analysis revealed significantly lover plasma K+ levels during the beetroot juice condition of this double-blind ranomized cross-over study after 600 m of the test, a third mechanism by which the supplementation protocol could have postponed fatigue would thus be the preservation of the electrical potential which is established by the distribution of K and Na ions inside, respectively outside of the muscle cell.
• increased oxidative capacity and consequent glucose sparing - Previous rodent studies have shown that nitrate supplementation increases blood flow and oxygenation of the muscle, the latter could translate into faster recovery of the glycogen content of the muscles in the short recovery phase.
• increased force production due to increased sarcoplasmic reticulum calcium release and force production - The increase in force would likewise have an energy sparing effect as it would mean that at a given exercise intensity (in watts) a lower number of muscle fibers would have to be recruited to get the job done. As with the previous information on the oxygenation of the muscle, this is yet based on observations in rodents and warrants verification in human studies.

Irrespective of the underlying mechanisms, it's likewise necessary to put them into perspective before we freak out and start raving about a new "superstar supplement" being born. After all, the effect size was significant, but comparably modest. A 2011 study by Mohr et al. for example observed a +16% performance increase after the ingestion of 6mg/kg caffeine in a subsequent Yo–Yo IR2 test (Mohr. 2011) and the effect simple training (i.e. +29% for sprint-endurance training; cf. Mohr. 2007) has on the perfomance in the same test, is likewise nothing to sneeze at.

So what did previous studies show?

As I have already hinted at in the red infobox a couple of paragraphs above, the dosage alone may explain why Wiley et al. did observe beneficial effects of nitrate / beetroot juice supplementation, while previous studies have shown very mixed results. Two other factors, I have highlighted in the following mini-overview (in bold and w/ an underline) that are probably relevant, are the training status of the study participants and the duration of the supplementation:

The combination of beta-alanine an baking soda (esp. the latter) may serve as a viable alternative for those trainees who are "too advanced" for nitrates to do the trick (read more)

You should by now be aware that orally ingested arginine does not induce significant NO boosts or performance increases, but did you know that it could help you get shredded? (read more)

• recreationally active and trained but sub-elite subjects, short-term dietary nitrate supplementation: 
• increased exercise tolerance at a fixed sub-maximal work rate (Bailey. 2009, 2010; Lansley. 2011b)
• increased power output during self-paced endurance exercise leading to improved cycle time-trial performance (Cermak.2012a; Lansley. 2011a).
• well-trained subjects (details in brackets) short-term dietary nitrate supplementation:
• higher mean power output in HIIT 6 x 500m rowing trial (rowers, Bond. 2012)
• little / no effect in endurance trained athletes in their respective disciplines (Besco. 2012; Cermak. 2012b; Christensen. 2013; Peacock. 2012; Wilkerson. 2012) 
•  recreationally active no regular, planned exercise, regimen chronic nitrate supplementation:
• reduced BP and the O₂ cost of submaximal exercise are maintained over 15d supplementation period (Vanhatalo. 2010)

The number of studies investigating the long-term effects of nitrate supplementation is to low to make a definite statement about whether or not it may be likely that short-term supplementation studies, in the course of which the researchers did not observe any ergogenic benefits of supplemental nitrate, would have yielded different results, if the supplementation had lasted for a couple of days or weeks.

Did you know that the scientists adjusted the comparatively high dosage of dietary nitrate the subjects received in the study at hand to the levels you would get, if you followed the anti-hypertensive DASH (Dietary Approaches to Stop Hypertension) diet? Obviously not an there is a good reason I am telling you that, 'cause this means that a paleo-ish high greens diet could in fact bring your nitrate levels into the same range as those of the subjects in the active trial of the study at hand - without having to spend a single buck on extra supplements, of course.

Nevertheless, the results Vanhatalo et al. present, namely that the effects persist in recreationally active subjects over 15 days of continuous supplementation, do actually stand in line with the hypothesis that the low / non-existent response in highly trained athletes could be due to their higher baseline NO3(-) and NO2(-) levels. I have invoked the latter in the discussion of the possible beneficial effects of NO generation in the previous discussion of the underlying mechanisms, already. If we assume that there is some sort of a saturation level and/or at least a logarithmic response to nitrate supplementation, where high baseline levels require even higher amounts of supplemental NO3(-) in order to bump the levels further up, we would have to conclude that

• highly trained athletes won't benefit from nitrate supplementation at all, because their blood NO3(-) levels are "saturated" and don't respond to supplementation
• highly trained athletes need way more nitrate to see a minimal increase in their NO3(-) levels

If the former was the case, nitrate supplementation would not make sense at all for highly trained athletes, if the latter was the case, it could produce benefits, but those would be much less pronounced than those observed in the study at hand or similar studies with recreationally active or even previously sedentary individuals.

Bottom line: I seriously can't tell you whether you will see significant performance increases from dietary nitrate supplementation. Unfortunately, especially those of you for whom even small increases in performance count, namely people with years of training under their belt, are probably the ones who benefit least. That being said, nitrates are probably not going to make it into the SuppVersity "must have" supplement list (read more about those in Part II of my recent interview w/ Sean Casey). The fact that they can have ergogenic effects, especially for HIIT and other "endurance-like" exercises with non-aerobic elements in themm is yet obviously indisputable. Whether they are worth the money effective dosages would cost you is yet highly questionable.... When I think about all the rest of purported ergogenics you can buy all over the Internet, a nitrate supplement or a 6-pack of beetroot juice are yet probably still better investments than 90% of the other "auxiliary" revenue,... ah pardon me, I mean "performance enhancers" the supplement market has to offer  ;-)


References:

• Atkins SJ. Performance of the Yo–Yo intermittent recovery test by elite professional and semiprofessional rugby league players. J Strength Cond Res. 2006; 20:222–225
• Bailey SJ, Winyard P, Vanhatalo A, Blackwell JR, DiMenna FJ, Wilkerson DP, Tarr J, Benjamin N, Jones AM. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Appl Physiol. 2009; 107:1144–1155.
• Besco´s R, Ferrer-Roca V, Galilea PA, Roig A, Drobnic F, Sureda A, Martorell M, Cordova A, Tur JA, Pons A. Sodium nitrate supplementation does not enhance performance of endurance athletes. Med Sci Sports Exerc. 2012; 44:2400–2409. 
• Bailey SJ, Fulford J, Vanhatalo A, Winyard PG, Blackwell JR, DiMenna FJ, Wilkerson DP, Benjamin N, Jones AM. Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercise in humans. J Appl Physiol. 2010; 109:135–148.
• Bond H, Morton L, Braakhuis AJ. Dietary nitrate supplementation improves rowing performance in well-trained rowers. Int J Sport Nutr Exerc Metab. 2012; 22:251–256.
• Christensen PM, Nyberg M, Bangsbo J. Influence of nitrate supplementation on VO(2) kinetics and endurance of elite Cyclists. Scand J Med Sci Sports. 2013. 23:e21–e31
• Cermak NM, Gibala MJ, van Loon LJ. Nitrate supplemen-tation’s improvement of 10-km time-trial performance in trained cyclists. Int J Sport Nutr Exerc Metab. 2012a; 22:64–71.
• Cermak NM, Res P, Stinkens R, Lundberg JO, Gibala MJ, van Loon L JC. No improvement in endurance performance following a single dose of beetroot juice. Int J Sport Nutr Exerc Metab. 2012b; 22:470–478.
• Dreissigacker U, Wendt M, Wittke T, Tsikas D, Maassen N. Positive correlation between plasma nitrite and performance during high-intensive exercise but not oxidative stress in healthy men. Nitric Oxide; 2010; 23:128–135
• Iaia FM, Thomassen M, Kolding H, Gunnarsson T, Wendell J, Rostgaard T, Nordsborg N, Krustrup P, Nybo L, Hellsten Y, Bangsbo J. Reduced volume but increased training intensity elevates muscle Na(-)–K(+) pump alpha1-subunit and NHE1 expression as well as short-term work capacity in humans. Am J Physiol Regul Integr Comp Physiol  2008; 294:R966–R974.
• Lansley KE, Winyard PG, Bailey SJ, Vanhatalo A, Wilkerson DP, Blackwell JR, Gilchrist M, Benjamin N, Jones AM. Acute dietary nitrate supplementation improves cycling time trial performance. Med Sci Sports Exerc. 2011a; 43:1125–1131
• Lansley KE, Winyard PG, Fulford J, Vanhatalo A, Bailey SJ, Blackwell JR, DiMenna FJ, Gilchrist M, Benjamin N, Jones AM. Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study. J Appl Physiol. 2011b; 110:591–600.
• Mohr M, Krustrup P, Nielsen JJ, Nybo L, Rasmussen MK, Juel C, Bangsbo J. Effect of two different intense training regimens on skeletal muscle ion transport proteins and fatigue development. Am J Physiol Regul Integr Comp Physiol. 2007; 292:R1594–R1602
• Mohr M, Nielsen JJ, Bangsbo J. Caffeine intake improves intense intermittent exercise performance and reduces muscle interstitial potassium accumulation. J Appl Physiol. 2011; 111:1372– 1379.
• Nemzer B, Pietrzkowski C, Spórna A, Stalica P, Thresher W, Michałowski T, Wybraniee, S. Betalainic and nutritional profiles of pigment-enriched red beet root (Beta vulgaris L.) dried extracts. Food Chemistry. 2011; 127:42–53. 
• Peacock O, Tjønna AE, James P, Wisløff U, Welde B, Bo¨hlke N, Smith A, Stokes K, Cook C, Sandbakk O. Dietary nitrate does not enhance running performance in elite cross-country skiers. Med Sci Sports Exerc. 2012; 44:2213–2219. 
• Totzeck M, Hendgen-Cotta UB, Rammos C, Frommke LM, Knack-stedt C, Predel HG, Kelm M, Rassaf T. Higher endog-enous nitrite levels are associated with superior exercise capacity in highly trained athletes. Nitric Oxide. 2012; 27:75–81
• Vanhatalo A, Bailey SJ, Blackwell JR, DiMenna FJ, Pavey TG, Wilkerson DP, Benjamin N, Winyard PG, Jones AM. Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise. Am J Physiol Regul Integr Comp Physiol. 2010; 299:R1121–R1131
• Veale JP, Pearce AJ, Carlson JS. The Yo–Yo intermittent recovery test (level 1) to discriminate elite junior Australian football players. J Sci Med Sport. 2010;  13:329–331.  
• Vernillo G, Silvestri A, Torre AL. The Yo–Yo intermittent recovery test in junior basketball players according to performance level and age group. J Strength Cond Res. 2012; 26:2490–2494.
• Wilkerson DP, Hayward GM, Bailey SJ, Vanhatalo A, Blackwell JR, Jones AM. Influence of acute dietary nitrate supplemen-tation on 50 mile time trial performance in well-trained cyclists. Eur J Appl Physiol. 2012; 112:4127–4134. 
• Wylie LJ, Mohr M, Krustrup P, Jackman SR, Ermιdis G, Kelly J, Black MI, Bailey SJ, Vanhatalo A, Jones AM. Dietary nitrate supplementation improves team sport-specific intense intermittent exercise performance. Eur J Appl Physiol. 2013 Feb 1.