Next Article in Journal
The Importance of Parents for Childhood and Adolescent Obesity Prevention: Should We Pay More Attention to Automatic Processes and Parental Stress?
Previous Article in Journal
Effect of Individual Nutrition Therapy and Exercise Regime on Gait Speed, Physical Function, Strength and Balance, Body Composition, Energy and Protein, in Injured, Vulnerable Elderly: A Multisite Randomized Controlled Trial (INTERACTIVE)
Review

Effects of Nitrate Supplementation on Exercise Performance in Humans: A Narrative Review

by 1,* and 2,3
1
Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana; Jamnikarjeva 10, 1000 Ljubljana, Slovenia
2
Department of Nephrology, University Medical Centre Ljubljana, Zaloška 7, 1000 Ljubljana, Slovenia
3
Faculty of Medicine, University of Ljubljana, Korytkova ulica 2, 1000 Ljubljana, Slovenia
*
Author to whom correspondence should be addressed.
Academic Editor: Gary D. Miller
Nutrients 2021, 13(9), 3183; https://doi.org/10.3390/nu13093183
Received: 25 July 2021 / Revised: 4 September 2021 / Accepted: 10 September 2021 / Published: 13 September 2021
(This article belongs to the Section Sports Nutrition)

Abstract

Nitrates have become increasingly popular for their potential role as an ergogenic aid. The purpose of this article was to review the current scientific evidence of nitrate supplementation on human performance. The current recommendation of nitrate supplementation is discussed, as well as possible health complications associated with nitrate intake for athletes, and dietary strategies of covering nitrate needs through sufficient intake of nitrate-rich foods alone are presented. Pubmed, Scopus, and Web of Science were searched for articles on the effects of nitrate supplementation in humans. Nitrates are an effective ergogenic aid when taken acutely or chronically in the range of ~5–16.8 mmol (~300–1041 mg) 2–3 h before exercise and primarily in the case of exercise duration of ~10–17 min in less trained individuals (VO2max < 65 mL/kg/min). Nitrate needs are most likely meet by ingesting approximately 250–500 g of leafy and root vegetables per day; however, dietary supplements might represent a more convenient and accurate way of covering an athlete’s nitrate needs. Athletes should refrain from mouthwash usage when nitrate supplementation benefits are desired. Future research should focus on the potential beneficial effects of nitrate supplementation on brain function, possible negative impacts of chronic nitrate supplementation through different nitrate sources, and the effectiveness of nitrate supplementation on strength and high-intensity intermittent exercise.
Keywords: nitrate; sports; performance; nitric oxide; dietary supplements; exercise science nitrate; sports; performance; nitric oxide; dietary supplements; exercise science

1. Introduction

Nitric oxide (NO) is a signaling molecule involved in numerous vascular and cellular functions, such as cellular respiration, vasodilation, and angiogenesis. NO is produced through both endogenous and exogenous pathways by dietary nitrate (NO3) ingestion. NO3 is an active compound found in certain NO3 rich vegetables and elicits potentially ergogenic as well as health-promoting effects. As such, NO3 presents as an interesting compound from both a sports perspective as an ergogenic aid as well as a potentially cost-effective tool for reducing the likelihood of cardiovascular events [1].
NO impacts exercise performance through several mechanisms: decreased fatigue during exercise, increased nutrient and oxygen delivery to the working muscles, and increased excretion of metabolic by-products of high-intensity exercise. There are several supplements promoted as so-called ‘NO boosters’. Historically, the amino acid L-arginine has been used extensively in these products to increase blood flow through NO production. Later, the non-essential amino-acid L-citrulline, found primarily in watermelons, cucumbers, and other melons, has replaced L-arginine in these supplements to a certain degree. Oral intake of L-citrulline as a dietary supplement increases the bioavailability of L-arginine to a greater extent than supplementation with L-arginine, as it is directly transported to the kidneys where it is converted to L-arginine, whereas L-arginine is subjected to catabolism via the enzyme arginase [2]. An extensive review of the literature on the effects of L-arginine and L-citrulline is beyond the scope of this article. However, it is worth noting that the positive effects of increased NO bioavailability may be induced through not only NO3 supplementation but potentially through L-arginine and L-citrulline supplementation as well.
NO3 supplementation and its effects on different types of exercise performance have gained attention in the past 2 decades. The purpose of this narrative review was to review the current scientific literature on the effects of NO3 supplementation on human performance, mechanisms by which NO3 may act as an ergogenic aid, and whether NO3 supplements are needed. The review was conducted using the online databases PubMed, Scopus, and Web of Science by searching keywords of ‘nitrate supplementation’ and ‘nitrate supplementation exercise performance’. Studies published up to September 2021 (English language restriction) were included. Studies completed in animal models or individuals with certain medical conditions were excluded from the review.

1.1. Nitrates: Mechanisms of Action as an Ergogenic Aid

NO3 may improve sports performance primarily through its effects on skeletal muscle, blood vessels, and the brain [3]. Increased NO availability can affect mitochondrial respiration and biogenesis, increase blood flow in active muscles during physical activity, and consequently reduce adenosine triphosphate (ATP) consumption during muscle contraction, and reduce oxygen consumption during aerobic exercise [4]. The effect of NO3 on blood vessels is manifested through blood pressure reduction, an observation also seen in otherwise healthy populations with blood pressure values in reference ranges. NO3 may also increase heat loss through the skin during physical activity [3]. Research on the effect of NO3 on the brain is currently in its infancy and is not as well understood as are the effects on skeletal muscles and blood vessels. As such, there is currently no direct evidence that the addition of NO3 could, in fact, increase the availability of NO in the brain. Nevertheless, research completed in animal models reports that NO in the brain reduces oxygen consumption during exercise [5], accelerates heat loss through the skin during physical activity [6], and potentially exhibits protective effects against exercise-induced hyperthermia [6,7].

1.2. Nitrates: Metabolism

NO is synthesized either by ingesting foods rich in NO3, L-arginine, L-citrulline, or through endogenous synthesis. NO synthesis from L-arginine takes place via its oxidation, catalyzed by the family of enzymes called nitric oxide synthase (NOS), and takes place in the presence of oxygen. The oxidation of L-arginine to NO was once thought to be the only way NO is formed in the body. However, we now know that this is not the case and that NO can be produced through the reduction of NO3 and nitrites (NO2) in the body [8]. NO formation via the NO3–NO2–NO pathway takes place with a gradual decrease in oxygen concentration (hypoxia), which occurs during intense physical activity. This pathway can be described as an alternative or complementary pathway of NO formation in the absence of oxygen to the aforementioned pathway via the amino acid L-arginine [9].
After ingestion of NO3 from diet or dietary supplements, plasma NO3 levels peak after approximately 1–2 h or after 2–3 h for NO2 before concentrations of both compounds gradually decrease and return to baseline levels after approximately 24 h [10].
Digestion of ingested NO3 and NO2 begins in the mouth, where a certain portion (~25%) of ingested NO3 is digested by saliva via anaerobic bacteria that reside there and reduce NO3 to NO2. The greater part of NO3 reduction takes place later in the stomach because of the low pH of the environment. Further reduction of NO2 takes place via a non-enzymatic reaction in the gastric lumen. Most of the circulating NO3 is eventually excreted through urine. However, approximately 20–25% of NO3 is taken up by the pancreas from the bloodstream and concentrated in saliva. The cycle of NO3 metabolism is thus completed and is then repeated, where the anaerobic bacteria in human saliva initially reduce NO3 to NO2. NO2 and remaining non-reduced NO3 is then swallowed again where a smaller percentage of NO2 is further reduced to NO by the low pH environment of the gastric lumen [9]. Most of the remaining NO2, however, re-enters the systemic circulation and is transported to specific locations throughout the body where they are reduced to NO via various enzymatic or non-enzymatic degradation pathways. The exact mechanism of NO2 re-entry into the circulation is unknown, but the reduction takes place primarily in the vascular system under conditions of hypoxia and reduced pH levels. Through the NO3–NO2–NO pathway of NO3 degradation, endogenously ingested nitrates are recycled by oral bacteria and act as a kind of reservoir of NO synthesis precursors [11].
It is important to note that this NO3 recycling process is severely impaired when oral mouthwashes are used on a regular basis as they destroy oral bacteria and consequently lower plasma NO3 levels [12,13]. This may be an important implication for athletes who should possibly be cautioned against mouthwash usage, especially during NO3 supplementation periods. Interestingly, chlorine-sterilized pool water does not seem to impair the NO3 reduction pathway through oral bacteria breakdown, as previously speculated by some. This has important implications for swimmers, a population where NO3 supplementation might be efficacious [14].

2. Nitrates and Exercise Performance

NO3 have been frequently researched over the past decade and a half in terms of their impact on sports performance in a wide variety of training modalities. One of the first of such studies reported positive effects of NO3 supplementation on time to exhaustion [15]. Afterward, NO3 supplementation was found to have a positive impact on lowering oxygen consumption and time to exhaustion [16].
Several other studies report positive benefits of NO3 intake, such as lowering blood pressure [17,18], reduced use of ATP and reduced degradation of phosphocreatine (PCr), improved muscle contractile efficiency [16], reduced oxygen consumption during submaximal exercise [19,20,21], and improved performance [16,19,22,23,24]. Conversely, many other studies do not report the above-mentioned positive effects [25,26,27,28,29,30,31]. A more detailed analysis of studies examining the effects of NO3 supplementations on exercise performance is presented in Table 1.
The observation that NO3 supplementation effects are less pronounced in better-trained individuals is also supported in a systematic review and meta-analysis by Campos et al. (2018) [3]. These researchers reported that despite the smaller impact of NO3 on the performance of well-trained individuals, the effect of NO3 should not be neglected. NO3 is currently regarded as one of a handful of dietary supplements with a direct, positive effect on athlete’s performance based on the latest consensus statement by the International Olympic Committee (IOC) [72]. The effect of NO3 supplementation on performance may be particularly desirable on competition day, where the differences between the competitors are marginal.
Additionally, diet may also influence NO3 supplementation effects in well-trained individuals. This effect, speculative in nature, relates to the general eating habits of elite athletes. We can assume that most top athletes include decent amounts of foods rich in NO3 as well as L-arginine and L-citrulline, making the effect of the dietary supplementation less pronounced [4]. Of course, the latter works solely on the assumption that the athlete consumes enough NO3-rich foods, and if the intake of NO3 from the diet is too low, dietary supplement usage will most likely yield greater benefits. A parallel may be drawn with creatine supplementation. Vegetarians and vegans who consume diets poorest in creatine (meat, fish, and eggs) have the lowest levels of muscle creatine phosphate, and the effect of creatine supplementation on performance is significantly more pronounced in this population versus omnivores [73].
Lastly, a difference in performance outcomes observed in studies using NO supplementation might be attributed to NO’s ability to interact with other free radicals. As NO half-life in vivo is in the order of a few seconds, this reaction might be dependent on its initial concentration [74], thus making it potentially problematic in the context of NO supplementation where a bolus of NO3 is ingested at once without the presence of other ingredients affecting its digestion. In this context, a major concern might be the interaction between NO and superoxide (O2) leading to peroxynitrite (OONO) formation—a highly reactive nitrogen species (RNS) affecting mitochondrial function, signal transduction, and stress response [75,76]. Chronic OONO formation might directly lead to the production of RNS and reactive oxygen species (ROS) in other subcellular compartments, leading to increased oxidative stress [77], which might affect performance. As with other supplements affecting oxidative stress, special emphasis on using such supplements in the right context might have to be taken when using NO3 supplementation. For example, high doses of vitamin C and E have been shown to blunt aerobic exercise adaptations [78,79]. High antioxidant usage has also been shown to blunt body composition improvements following a resistance training protocol [80]. This might limit the usage of such supplements during specific conditions where an athlete’s recovery is more important than optimal adaptation (e.g., tournaments where an athlete has many competitions in a short time frame). For NO3 supplementation, no such guidelines can be given, and to our knowledge, no research has looked directly into differences in RNS formation from NO3 supplementation or via NO3 rich diet but should be taken into account, especially when chronic NO3 supplementation is being considered.
There are also several literature reviews and meta-analyses examining the effectiveness of NO3 supplementation on exercise performance. Hoon et al. (2013) reported a statistically significant improvement in performance for constant power/speed tests and smaller, statistically insignificant but positive effects in the case of incremental tests and time trials [81]. However, the meta-analysis did not consider differences in NO3 supplementation protocols between trials as well as the training status of individuals. Pawlak-Chaouch et al. published a meta-analysis including 26 randomized and placebo-controlled studies in 2016 and reported a significant reduction in VO2 during submaximal exercise [82]. Afterward, a meta-analysis by Van De Wall and Vukovich in 2018 reported that NO3 supplementation can improve tolerance to and efficiency of continuous high-intensity exercise and maximal exercise with increasing intensity [4]. The authors recommend the effectiveness of both acute as well as chronic NO3 supplementation (up to 15 days) when taken in an amount of 5–9 mmol with similar conclusions being found in a meta-analysis by McMahon et al. (2016) on the impact of NO3 supplementation specifically on endurance performance [83]. This meta-analysis included 47 studies and reported that the effect of NO3 supplementation was efficient on submaximal aerobic capacity, but lower effectiveness for time trial tests, which is in line with past research by Hoon et al. (2013) [81].

2.1. Nitrates: Supplementation Protocol

Even though a linear correlation exists between the amount of NO3 ingested and the increase in plasma NO3 levels, we can assume that there is an upper limit of NO3 intake that still elicits a positive effect on performance. Wylie et al. (2013) reported that ingestion of 4.2 mmol NO3 did not affect VO2 during moderate-intensity cycling, but VO2 was affected by NO3 supplemented at 8.4 mmol and 16.8 mmol [39]. However, ingestion of 16.8 mmol NO3 compared to 8.4 mmol NO3 did not provide additional benefits. Thus, we can assume that the effect of NO3 on performance exists within a specific interval. This interval is most likely between 5–9 mmol (310–560 mg) NO3 taken either acutely 2–3 h before exercise [41] or chronically over an extended period [4]. Similar recommendations can also be found from the IOC [72] and Senefeld et al. (2020) [84]. The authors of the latter meta-analysis report that the effect of NO3 is not statistically significant if NO3 is taken less than 2 h before exercise as this does not allow enough time for NO3 to NO conversion.
The effect of acute or chronic NO3 intake is expected to be similar based on the current literature [84]; however, chronic NO3 intake of more than 3 consecutive days before the race may potentially reap greater benefits for well-trained athletes [85].

2.2. Nitrates: Effects of Exercise Type and Conditions

The IOC reports the effectiveness of NO3 differs across not only training status but exercise type and trial duration as well [72]. As such, the impact of NO3 supplementation is reported to be in the range of 4–25% for time to exhaustion tests and 1–3 % for sport-specific tests lasting less than 40 min. NO3 is expected to have the greatest effect between the range of approximately 12 and 40 min. Furthermore, within this time frame, the effects of NO3 supplementation are likely most pronounced for exercise lasting between 601 and 999 s (~10–17 min), with the effects of NO3 being effective regardless of normoxic or hypoxic conditions [84].
Effects of NO3 supplementation have been studied in a wide variety of performance tests. However, the effects are most likely especially pronounced in time to exhaustion tests rather than time trial tests or incremental power tests. This may be due to the fact that time to exhaustion tests are supposedly better at measuring an athlete’s endurance capacity and are highly influenced by psychological factors (e.g., motivation, boredom, etc.) [3,86]. As for the type of exercise, Senefeld et al. (2020) report a significant effect of NO3 on cycling and running, the most commonly studied training modalities in research on NO3 supplementation, but not in knee extension tests or rowing rests. However, the lack of effect is most likely due to the relatively low proportion of studies completed on these two forms of performance tests rather than the exercise type per se [84].
NO3 might be particularly effective for team sports athletes because of their potential beneficial effect on cognition. Athletes who participate in team sports are forced to make many quick decisions during training and competition. However, prolonged high-intensity exercise can have a negative impact on reaction time and task performance [87]. Thompson et al. (2015) reported a statistically significantly shorter reaction time in individuals receiving NO3 supplementation in the amount of 6.4 mmol to 12.8 mmol for 7 consecutive days [88]. These positive effects of NO3 supplementation on cognition may arise from the positive effect of NO on neurovascular coupling [89] and increased cerebral perfusion, primarily in the prefrontal cortex responsible for executive function [90]. NO3 thus has a potentially positive effect on reducing the decline in cognitive function, primarily athlete’s reaction time, which is otherwise associated with repetitive high-intensity intermittent exercise.
A large majority of studies on NO3 supplementation effects on performance have been completed on endurance tests. Some research, however, focuses on investigating these effects on high-intensity exercise and strength, where mixed results are observed. Thompson et al. (2016) reported improvements in sprints in the Yo-Yo test after NO3 supplementation [91]. A similar effect in the same test in a sample of 32 football players is also reported by Nyakayiru et al. (2017) [24]. Cuenca et al. (2018) also reported an ergogenic effect of acute NO3 intake of 6.4 mmol in the Wingate test, primarily in the first half of the sprints [50]. However, Martin et al. (2014) do not report a positive effect of NO3 on the protocol of 8 s sprints with 30 s pauses [43].
A systematic review by San Juan et al. (2020) on the effect of NO3 on weight training in an otherwise limited sample of four studies reported a positive effect of NO3 on upper body strength and the number of repetitions performed in upper body strength test (bench press) as well as lower body strength test (squat) [92]. We certainly need more research into the impact of NO3 on high-intensity exercise and strength, but preliminary results suggest that NO3 could be beneficial in this sport context as well.
Another avenue of NO3 effects on performance is research completed in extreme conditions, such as hypoxic and cold environmental settings (e.g., mountaineering, skiing, altitude training, etc.). As altitude increases, hypoxic conditions reduce O2 availability and decrease exercise performance. We can somewhat overcome this problem with altitude acclimatization; however, this process may take up to several weeks to fully manifest, which is not always possible in certain sports situations. Additionally, physical fitness otherwise seen at sea level might not ever be fully regained, even with prolonged acclimatization [93]. It is suggested that NO plays an essential role in hypoxia-induced vasodilatation, thereby ensuring adequate O2 availability to the working muscle and brain tissue during hypoxic conditions [94,95]. Certain populations native to higher altitudes (e.g., Sherpa) have been proposed to exert abnormal hypoxic tolerance in part due to elevated circulating levels of NO [96]. Indeed, research completed at simulated altitude shows the benefits of NO3 supplementation on certain physiological parameters (e.g., improved mitochondrial respiration, O2 consumption during exercise, etc.). However, these findings do not seem to be observed in field tests at ’real’ altitudes, making real-world applications limited [93,96,97]. Certain researchers have postulated that chronic NO3 supplementation might even be detrimental for athletes training at altitude from a perspective of possibly blunting hypoxic adaptations by decreasing arterial and muscle O2 saturation, which may act as a signal for such adaptations [98]. As such, there is currently no clear benefit of NO3- supplementation for athletes performing at high altitudes, and more research is needed on this specific topic.

2.3. Nitrates: Food Sources and Supplementation

The primary sources of NO3 and NO2 is either through NO3 rich foods or through endogenous productions. Of these pathways, nutrition represents the one with greater potential to supply the body with a higher amount of NO3 as the endogenous supply of NO3 is relatively limited, and only a bowl of green leafy vegetables contains a higher amount of NO3 than is formed endogenously throughout the entire day [9]. Athletes should thus be advised to meet their NO3 through nutrition, either with NO3 supplementation or through NO3 rich foods—primarily leafy greens and root vegetables.
However, the NO3 content of these vegetables varies greatly, as it depends on many factors such as the origin of the vegetable, the quality and pH of the soil in which the vegetables are grown, type and frequency of nitrogen fertilizers, type of vegetable cultivation, time of vegetable harvesting, age of the plant at harvest, conditions of vegetable storage and weather conditions in which vegetables are grown, and method of vegetable preparation, etc. [99].
Given all these factors, it is difficult to make a specific recommendation for athletes to meet the needs of NO3 via the diet due to the large number of variable factors that affect the NO3 content in the diet. Speculations can be made based on current data on the average NO3 of NO3 rich foods (e.g., beetroot, endive, fennel, kohlrabi, lettuce, pak choi, radish, rocket, and spinach) that this figure would be set at 150 g of aforementioned foods at the lowest [100]. However, this number might be significantly higher or possibly lower in some cases, depending on the above-mentioned factors. As a higher vegetable intake than 150 g is generally recommended, athletes should probably be encouraged to ingest approximately 250–500 g of leafy and root vegetables per day to ensure adequate NO3 intake.
Additionally, ingesting a bolus of NO3 via supplementation might hold a greater risk of peroxynitrite production relative to covering NO3 needs through diet. This might be another limiting factor of NO3 supplementation, as discussed in the chapter titled ’Nitrates and exercise performance’.
Lastly, NO3 in the form of a dietary supplement may represent a more convenient and accurate way to cover the needs for NO3; however, as with any other dietary supplement, there is always the possibility of supplement contamination [101], and an athlete’s budget must also be considered.

3. Conclusions

Based on current literature, NO3 represents an effective ergogenic aid for improving performance through various mechanisms and is useful in a variety of sports situations and exercise modalities. The effect of NO3 is most pronounced in less-trained individuals when taken acutely or chronically in the range of ~5–16.8 mmol (~300–1041 mg NO3) 2–3 h before exercise and primarily in the case of exercise duration of ~10–17 min. Nitrate supplementation is less pronounced in well-trained individuals (VO2max > 65 mL/kg/min); however, it might still be desirable, especially during competition. Athletes should refrain from mouthwash usage when nitrate supplementation benefits are desired.
NO3 is found in certain vegetables, but due to many variable factors, we cannot make exact recommendations to cover these needs through diet alone. Given that there is a potential for supplement contamination, it would make sense to explore how dietary needs for NO3 can be covered through dietary sources. Currently, speculations can be made that this figure is roughly 250–500 g of leafy and root vegetables per day. Dietary supplements might represent a more convenient and accurate way of covering one’s needs for nitrate; however, potential supplement contamination and an athlete’s budget must be considered.
Future research should focus on the potential beneficial effects of NO3 on the brain, especially in regard to sport-specific situations, and on the effectiveness of NO3 in strength training and high-intensity intermittent training.

Author Contributions

Conceptualization, M.M. and B.K.; methodology, M.M.; validation, M.M. and B.K.; formal analysis, M.M.; investigation, M.M.; resources, M.M.; data curation, M.M.; writing—original draft preparation, M.M.; writing—review and editing, M.M.; visualization, B.K.; supervision, B.K.; project administration, B.K.; funding acquisition, B.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Clements, W.T.; Lee, S.; Bloomer, R.J. Nitrate ingestion: A review of the health and physical performance effects. Nutrients 2014, 6, 5224–5264. [Google Scholar] [CrossRef] [PubMed]
  2. Gonzalez, A.M.; Trexler, E.T. Effects of Citrulline Supplementation on Exercise Performance in Humans: A Review of the Current Literature. J. Strength Cond. Res. 2020, 34, 1480–1495. [Google Scholar] [CrossRef] [PubMed]
  3. Campos, H.O.; Drummond, L.R.; Rodrigues, Q.T.; Machado, F.S.M.; Pires, W.; Wanner, S.P.; Coimbra, C.C. Nitrate supplementation improves physical performance specifically in non-athletes during prolonged open-ended tests: A systematic review and meta-analysis. Br. J. Nutr. 2018, 119, 636–657. [Google Scholar] [CrossRef]
  4. Van De Walle, G.P.; Vukovich, M.D. The Effect of Nitrate Supplementation on Exercise Tolerance and Performance: A Systematic Review and Meta-Analysis. J. Strength Cond. Res. 2018, 32, 1796–1808. [Google Scholar] [CrossRef]
  5. Lacerda, A.C.R.; Marubayashi, U.; Balthazar, C.H.; Coimbra, C.C. Evidence that brain nitric oxide inhibition increases metabolic cost of exercise, reducing running performance in rats. Neurosci. Lett. 2006, 393, 260–263. [Google Scholar] [CrossRef]
  6. Wanner, S.P.; Leite, L.H.R.; Guimarães, J.B.; Coimbra, C.C. Increased brain L-arginine availability facilitates cutaneous heat loss induced by running exercise. Clin. Exp. Pharmacol. Physiol. 2015, 42, 609–616. [Google Scholar] [CrossRef]
  7. Lacerda, A.C.R.; Marubayashi, U.; Coimbra, C.C. Nitric oxide pathway is an important modulator of heat loss in rats during exercise. Brain Res. Bull. 2005, 67, 110–116. [Google Scholar] [CrossRef] [PubMed]
  8. Jones, A.M. Dietary nitrate supplementation and exercise performance. Sports Med. 2014, 44, 35–45. [Google Scholar] [CrossRef]
  9. Lundberg, J.O.; Weitzberg, E.; Gladwin, M.T. The nitrate-nitrite-nitric oxide pathway in physiology and therapeutics. Nat. Rev. Drug Discov. 2008, 7, 156–167. [Google Scholar] [CrossRef]
  10. Webb, A.J.; Patel, N.; Loukogeorgakis, S.; Okorie, M.; Aboud, Z.M.; Misra, S.; Rashid, R.; Miall, P.; Deanfield, J.; Benjamin, N.; et al. Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite. Hypertension 2008, 51, 784–790. [Google Scholar] [CrossRef] [PubMed]
  11. Stanaway, L.; Rutherfurd-Markwick, K.; Page, R.; Ali, A. Performance and Health Benefits of Dietary Nitrate Supplementation in Older Adults: A Systematic Review. Nutrients 2017, 9, 1171. [Google Scholar] [CrossRef] [PubMed]
  12. Clifford, T.; Howatson, G.; West, D.J.; Stevenson, E.J. The Potential Benefits of Red Beetroot Supplementation in Health and Disease. Nutrients 2015, 7, 2801–2822. [Google Scholar] [CrossRef] [PubMed]
  13. McDonagh, S.T.J.; Wylie, L.J.M.; Winyard, P.G.; Vanhatalo, A.; Jones, A.M. The Effects of Chronic Nitrate Supplementation and the Use of Strong and Weak Antibacterial Agents on Plasma Nitrite Concentration and Exercise Blood Pressure. Int. J. Sports Med. 2015, 36, 1177–1185. [Google Scholar] [CrossRef]
  14. Rowland, S.N.; Chessor, R.; French, G.; Robinson, G.P.; O’Donnell, E.; James, L.J.; Bailey, S.J. Oral nitrate reduction is not impaired after training in chlorinated swimming pool water in elite swimmers. Appl. Physiol. Nutr. Metab. 2021, 46, 86–89. [Google Scholar] [CrossRef] [PubMed]
  15. Larsen, F.J.; Weitzberg, E.; Lundberg, J.O.; Ekblom, B. Effects of dietary nitrate on oxygen cost during exercise. Acta Physiol. 2007, 191, 59–66. [Google Scholar] [CrossRef]
  16. Bailey, S.J.; Winyard, P.; Vanhatalo, A.; Blackwell, J.R.; Dimenna, F.J.; Wilkerson, D.P.; Tarr, J.; Benjamin, N.; Jones, A.M. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J. Appl. Physiol. (1985) 2009, 107, 1144–1155. [Google Scholar] [CrossRef]
  17. Bailey, S.J.; Fulford, J.; Vanhatalo, A.; Winyard, P.G.; Blackwell, P.R.; DiMenna, F.J.; Wilkerson, D.P.; Benjamin, N.; Jones, A.M. Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercise in humans. J. Appl. Physiol. (1985) 2010, 109, 135–148. [Google Scholar] [CrossRef] [PubMed]
  18. Vanhatalo, A.; Bailey, S.J.; Blackwell, J.R.; DiMenna, F.J.; Pavey, T.G.; Wilkerson, D.P.; Benjamin, N.; Winyard, P.G.; Jones, A.M. 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. [Google Scholar] [CrossRef] [PubMed]
  19. Masschelein, E.; Van Thienen, R.; Wang, X.; Van Schepdael, A.; Thomis, M.; Hespel, P. Dietary nitrate improves muscle but not cerebral oxygenation status during exercise in hypoxia. J. Appl. Physiol. (1985) 2012, 113, 736–745. [Google Scholar] [CrossRef]
  20. Muggeridge, D.J.; Howe, C.C.F.; Spendiff, O.; Pedlar, C.; James, P.E.; Easton, C. The effects of a single dose of concentrated beetroot juice on performance in trained flatwater kayakers. Int. J. Sport Nutr. Exerc. Metab. 2013, 23, 498–506. [Google Scholar] [CrossRef] [PubMed]
  21. Porcelli, S.; Ramaglia, M.; Bellistri, G.; Pavei, G.; Pugliese, L.; Montorsi, M.; Rasica, L.; Marzorati, M. Aerobic Fitness Affects the Exercise Performance Responses to Nitrate Supplementation. Med. Sci. Sports Exerc. 2015, 47, 1643–1651. [Google Scholar] [CrossRef] [PubMed]
  22. Lansley, K.E.; Winyard, P.G.; Bailey, S.J.; Vanhatalo, A.; Wilkerson, D.P.; Blackwell, J.R.; Gilchrist, M.; Benjamin, N.; Jones, A.M. Acute dietary nitrate supplementation improves cycling time trial performance. Med. Sci. Sports Exerc. 2011, 43, 1125–1131. [Google Scholar] [CrossRef]
  23. Murphy, M.; Eliot, K.; Heuertz, R.M.; Weiss, E. Whole beetroot consumption acutely improves running performance. J. Acad. Nutr. Diet. 2012, 112, 548–552. [Google Scholar] [CrossRef] [PubMed]
  24. Nyakayiru, J.; Jonvik, K.L.; Trommelen, J.; Pinckaers, P.J.M.; Senden, J.M.; van Loon, L.J.C.; Verdijk, L.B. Beetroot Juice Supplementation Improves High-Intensity Intermittent Type Exercise Performance in Trained Soccer Players. Nutrients 2017, 9, 314. [Google Scholar] [CrossRef] [PubMed]
  25. Cermak, N.M.; Res, P.; Stinkens, R.; Lundberg, J.O.; Gibala, M.J.; van Loon, L.J.C. No improvement in endurance performance after a single dose of beetroot juice. Int. J. Sport Nutr. Exerc. Metab. 2012, 22, 470–478. [Google Scholar] [CrossRef] [PubMed]
  26. Christensen, P.M.; Nyberg, M.; Bangsbo, J. Influence of nitrate supplementation on VO₂ kinetics and endurance of elite cyclists. Scand. J. Med. Sci. Sports 2013, 23, e21–e31. [Google Scholar] [CrossRef]
  27. McQuillan, J.; Dulson, D.; Laursen, P.; Kilding, A. Dietary Nitrate Fails to Improve 1 and 4km Cycling Performance in Highly-Trained Cyclists. Int. J. Sport Nutr. Exerc. Metab. 2017, 27, 1–26. [Google Scholar] [CrossRef]
  28. McQuillan, J.A.; Dulson, D.K.; Laursen, P.B.; Kilding, A.E. The Effect of Dietary Nitrate Supplementation on Physiology and Performance in Trained Cyclists. Int. J. Sports Physiol. Perform. 2017, 12, 684–689. [Google Scholar] [CrossRef]
  29. Nyakayiru, J.M.; Jonvik, K.L.; Pinckaers, P.J.M.; Senden, J.; van Loon, L.J.C.; Verdijk, L.B. No Effect of Acute and 6-Day Nitrate Supplementation on VO2 and Time-Trial Performance in Highly Trained Cyclists. Int. J. Sport. Nutr. Exerc. Metab. 2017, 27, 11–17. [Google Scholar] [CrossRef]
  30. Peacock, O.; Tjønna, A.E.; James, P.; Wisløff, U.; Welde, B.; Böhlke, 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. [Google Scholar] [CrossRef]
  31. Wilkerson, D.P.; Hayward, G.M.; Bailey, S.J.; Vanhatalo, A.; Blackwell, J.R.; Jones, A.M. Influence of acute dietary nitrate supplementation on 50 mile time trial performance in well-trained cyclists. Eur. J. Appl. Physiol. 2012, 112, 4127–4134. [Google Scholar] [CrossRef]
  32. Larsen, F.J.; Weitzberg, E.; Lundberg, J.O.; Ekblom, B. Dietary nitrate reduces maximal oxygen consumption while maintaining work performance in maximal exercise. Free. Radic. Biol. Med. 2010, 48, 342–347. [Google Scholar] [CrossRef]
  33. Vanhatalo, A.; Fulford, J.; Bailey, S.J.; Blackwell, J.R.; Winyard, P.G.; Jones, A.M. Dietary nitrate reduces muscle metabolic perturbation and improves exercise tolerance in hypoxia. J. Physiol. 2011, 589, 5517–5528. [Google Scholar] [CrossRef] [PubMed]
  34. Bescos, R.; Ferrer-Roca, V.; Galilea, P.A.; Roig, A.; Drobnic, F.; Sureda, A.; Martorell, M.; Cordova, A.; Tur, J.A.; Pons, A. Sodium Nitrate Supplementation Does Not Enhance Performance of Endurance Athletes. Med. Sci. Sports Exerc. 2012, 44, 2400–2409. [Google Scholar] [CrossRef] [PubMed]
  35. Bond, H.; Morton, L.; Braakhuis, A.J. Dietary nitrate supplementation improves rowing performance in well-trained rowers. Int J. Sport Nutr. Exerc. Metab. 2012, 22, 251–256. [Google Scholar] [CrossRef]
  36. Cermak, N.M.; Gibala, M.J.; van Loon, L.J.C. Nitrate supplementation’s improvement of 10-km time-trial performance in trained cyclists. Int. J. Sport. Nutr. Exerc. Metab. 2012, 22, 64–71. [Google Scholar] [CrossRef]
  37. Kelly, J.; Vanhatalo, A.; Wilkerson, D.; Wylie, L.; Jones, A. Effects of Nitrate on the Power–Duration Relationship for Severe-Intensity Exercise. Med. Sci. Sports Exercise. 2013, 45, 1798–1806. [Google Scholar] [CrossRef]
  38. Breese, B.C.; McNarry, M.A.; Marwood, S.; Blackwell, J.R.; Bailey, S.J.; Jones, A.M. Beetroot juice supplementation speeds O2 uptake kinetics and improves exercise tolerance during severe-intensity exercise initiated from an elevated metabolic rate. Am. J. Physiol. Regul. Integr. Comp. Physiol. 2013, 305, R1441–R1450. [Google Scholar] [CrossRef]
  39. Wylie, L.J.; Kelly, J.; Bailey, S.J.; Blackwell, J.R.M.; Skiba, P.F.; Winyard, P.G.; Jeukendrup, A.E.; Vanhatalo, A.; Jones, A.M. Beetroot juice and exercise: Pharmacodynamic and dose-response relationships. J. Appl. Physiol. (1985) 2013, 115, 325–336. [Google Scholar] [CrossRef] [PubMed]
  40. Wylie, L.J.; Mohr, M.; Krustrup, P.; Jackman, S.R.; Ermιdis, G.; Kelly, J.; Black, M.I.; Bailey, S.J.; Vanhatalo, A.; Jones, A.M. Dietary nitrate supplementation improves team sport-specific intense intermittent exercise performance. Eur. J. Appl. Physiol. 2013, 113, 1673–1684. [Google Scholar] [CrossRef]
  41. Hoon, M.W.; Jones, A.M.; Johnson, N.A.; Blackwell, J.R.; Broad, E.M.; Lundy, B.M.; Rice, A.J.; Burke, L.M. The effect of variable doses of inorganic nitrate-rich beetroot juice on simulated 2,000-m rowing performance in trained athletes. Int. J. Sports Physiol. Perform. 2014, 9, 615–620. [Google Scholar] [CrossRef]
  42. Boorsma, R.K.; Whitfield, J.; Spriet, L.L. Beetroot juice supplementation does not improve performance of elite 1500-m runners. Med. Sci. Sports Exerc. 2014, 46, 2326–2334. [Google Scholar] [CrossRef]
  43. Martin, K.; Smee, D.; Thompson, K.G.; Rattray, B. No improvement of repeated-sprint performance with dietary nitrate. Int. J. Sports Physiol. Perform. 2014, 9, 845–850. [Google Scholar] [CrossRef]
  44. Peeling, P.; Cox, G.R.; Bullock, N.; Burke, L.M. Beetroot Juice Improves On-Water 500 M Time-Trial Performance, and Laboratory-Based Paddling Economy in National and International-Level Kayak Athletes. Int. J. Sport. Nutr. Exerc. Metab. 2015, 25, 278–284. [Google Scholar] [CrossRef]
  45. Wylie, L.J.; Bailey, S.J.; Kelly, J.; Blackwell, J.R.; Vanhatalo, A.; Jones, A.M. Influence of beetroot juice supplementation on intermittent exercise performance. Eur. J. Appl. Physiol. 2015, 116, 415–425. [Google Scholar] [CrossRef] [PubMed]
  46. Christensen, P.M.; Petersen, N.K.; Friis, S.N.; Weitzberg, E.; Nybo, L. Effects of nitrate supplementation in trained and untrained muscle are modest with initial high plasma nitrite levels. Scand. J. Med. Sci. Sports 2017, 27, 1616–1626. [Google Scholar] [CrossRef]
  47. Vasconcellos, J.; Henrique Silvestre, D.; Dos Santos Baião, D.; Werneck-de-Castro, J.P.; Silveira Alvares, T.; Paschoalin, V.M.F. A Single Dose of Beetroot Gel Rich in Nitrate Does Not Improve Performance but Lowers Blood Glucose in Physically Active Individuals. J. Nutr. Metab. 2017, 2017, 7853034. [Google Scholar] [CrossRef] [PubMed]
  48. Shannon, O.M.; Barlow, M.J.; Duckworth, L.; Williams, E.; Wort, G.; Woods, D.; Siervo, M.; O’Hara, J.P. Dietary nitrate supplementation enhances short but not longer duration running time-trial performance. Eur. J. Appl. Physiol. 2017, 117, 775–785. [Google Scholar] [CrossRef]
  49. de Castro, T.F.; de Assis Manoel, F.; Figueiredo, D.H.; Figueiredo, D.H.; Machado, F.A. Effect of beetroot juice supplementation on 10-km performance in recreational runners. Appl. Physiol. Nutr. Metab. 2019, 44, 90–94. [Google Scholar] [CrossRef] [PubMed]
  50. Cuenca, E.; Jodra, P.; Pérez-López, A.; González-Rodríguez, L.G.; da Silva, S.F.; Veiga-Herreros, P.; Domínguez, R. Effects of Beetroot Juice Supplementation on Performance and Fatigue in a 30-s All-Out Sprint Exercise: A Randomized, Double-Blind Cross-Over Study. Nutrients 2018, 10, 1222. [Google Scholar] [CrossRef]
  51. Oskarsson, J.; McGawley, K. No individual or combined effects of caffeine and beetroot-juice supplementation during submaximal or maximal running. Appl. Physiol. Nutr. Metab. 2018, 43, 697–703. [Google Scholar] [CrossRef]
  52. Jo, E.; Fischer, M.; Auslander, A.T.; Beigarten, A.; Daggy, B.; Hansen, K.; Kessler, L.; Osmond, A.; Wang, H.; Wes, R. The Effects of Multi-Day vs. Single Pre-exercise Nitrate Supplement Dosing on Simulated Cycling Time Trial Performance and Skeletal Muscle Oxygenation. J. Strength Cond. Res. 2019, 33, 217–224. [Google Scholar] [CrossRef]
  53. Rokkedal-Lausch, T.; Franch, J.; Poulsen, M.K.; Thomsen, L.P.; Weitzberg, E.; Kamavuako, E.N.; Karbing, D.S.; Larsen, R.G. Chronic high-dose beetroot juice supplementation improves time trial performance of well-trained cyclists in normoxia and hypoxia. Nitric Oxide 2019, 85, 44–52. [Google Scholar] [CrossRef]
  54. Esen, O.; Nicholas, C.; Morris, M.; Bailey, S.J. No Effect of Beetroot Juice Supplementation on 100-m and 200-m Swimming Performance in Moderately Trained Swimmers. Int. J. Sports Physiol. Perform. 2019, 14, 706–710. [Google Scholar] [CrossRef] [PubMed]
  55. Wickham, K.A.; McCarthy, D.G.; Pereira, J.M.; Cervone, D.T.; Verdijk, L.B.; van Loon, L.C.J.; Power, G.A.; Spriet, L.L. No effect of beetroot juice supplementation on exercise economy and performance in recreationally active females despite increased torque production. Physiol. Rep. 2019, 7, e13982. [Google Scholar] [CrossRef]
  56. Kent, G.L.; Dawson, B.; McNaughton, L.R.; Cox, G.R.; Burke, L.M.; Peeling, P. The effect of beetroot juice supplementation on repeat-sprint performance in hypoxia. J. Sports Sci. 2019, 37, 339–346. [Google Scholar] [CrossRef] [PubMed]
  57. Mosher, S.L.; Gough, L.A.; Deb, S.; Saunders, B.; Mc Naughton, L.R. High dose Nitrate ingestion does not improve 40 km cycling time trial performance in trained cyclists. Res. Sports Med. 2019, 28, 138–146. [Google Scholar] [CrossRef] [PubMed]
  58. Ranchal-Sanchez, A.; Diaz-Bernier, V.M.; De La Florida-Villagran, C.A.; Llorente-Cantarero, F.J.; Campos-Perez, J.; Jurado-Castro, J.M. Acute Effects of Beetroot Juice Supplements on Resistance Training: A Randomized Double-Blind Crossover. Nutrients 2020, 12, 1912. [Google Scholar] [CrossRef] [PubMed]
  59. López-Samanes, Á.; Pérez-López, A.; Moreno-Pérez, V.; Nakamura, F.Y.; Acebes-Sánchez, J.; Quintana-Milla, I.; Sánchez-Oliver, A.J.; Moreno-Pérez, D.; Fernández-Elías, V.E.; Domínguez, R. Effects of Beetroot Juice Ingestion on Physical Performance in Highly Competitive Tennis Players. Nutrients 2020, 12, 584. [Google Scholar] [CrossRef]
  60. Liubertas, T.; Kairaitis, R.; Stasiule, L.; Viskelis, P.; Viškelis, J.; Urbonaviciene, D. The influence of amaranth (Amaranthus hypochondriacus) dietary nitrates on the aerobic capacity of physically active young persons. J. Int. Soc. Sport Nutr. 2020, 17, 37. [Google Scholar] [CrossRef]
  61. Rodríguez-Fernández, A.; Castillo, D.; Raya-González, J.; Domínguez, R.; Bailey, S.J. Beetroot juice supplementation increases concentric and eccentric muscle power output. Original Investigation. J. Sports Sci. Med. 2020, 24. [Google Scholar] [CrossRef]
  62. Jonvik, K.L.; Hoogervorst, D.; Peelen, H.B.; de Niet, M.; Verdijk, L.B.; van Loon, L.J.C.; van Dijk, J.W. The impact of beetroot juice supplementation on muscular endurance, maximal strength and countermovement jump performance. Eur. J. Sport Sci. 2021, 21, 871–878. [Google Scholar] [CrossRef]
  63. Dumar, A.M.; Huntington, A.F.; Rogers, R.R.; Kopec, T.J.; Williams, T.D.; Ballmann, C.G. Acute Beetroot Juice Supplementation Attenuates Morning-Associated Decrements in Supramaximal Exercise Performance in Trained Sprinters. Int. J. Env. Res. Public Health 2021, 18, 412. [Google Scholar] [CrossRef]
  64. Marshall, A.R.; Rimmer, J.E.; Shah, N.; Bye, K.; Kipps, C.; Woods, D.R.; O’Hara, J.; Boos, C.J.; Barlow, M. Marching to the Beet: The effect of dietary nitrate supplementation on high altitude exercise performance and adaptation during a military trekking expedition. Nitric Oxide 2021, 113–114, 70–77. [Google Scholar] [CrossRef]
  65. Fowler, R.; Jeffries, O.; Tallent, J.; Theis, N.; Heffernan, S.M.; McNarry, M.A.; Kilduff, L.; Waldron, M. No thermoregulatory or ergogenic effect of dietary nitrate among physically inactive males, exercising above gas exchange threshold in hot and dry conditions. Eur. J. Sport Sci. 2021, 21, 370–378. [Google Scholar] [CrossRef] [PubMed]
  66. Townsend, J.R.; Hart, T.L.; Haynes, J.T., 4th; Woods, C.A.; Toy, A.M.; Pihera, B.C.; Aziz, M.A.; Zimmerman, G.A.; Jones, M.D.; Vantrease, W.C.; et al. Influence of Dietary Nitrate Supplementation on Physical Performance and Body Composition Following Offseason Training in Division I Athletes. J. Diet. Suppl. 2021, 1–16. [Google Scholar] [CrossRef]
  67. Andersen, P.; Henriksson, J. Capillary supply of the quadriceps femoris muscle of man: Adaptive response to exercise. J. Physiol. 1977, 270, 677–690. [Google Scholar] [CrossRef] [PubMed]
  68. Poveda, J.J.; Riestra, A.; Salas, E.; Cagigas, M.L.; López-Somoza, C.; Amado, J.A.; Berrazueta, J.R. Contribution of nitric oxide to exercise-induced changes in healthy volunteers: Effects of acute exercise and long-term physical training. Eur. J. Clin. Investig. 1997, 27, 967–971. [Google Scholar] [CrossRef]
  69. Nevill, A.M.; Brown, D.; Godfrey, R.; Johnson, P.J.; Romer, L.; Stewart, A.D.; Winter, E.M. Modeling Maximum Oxygen Uptake of Elite Endurance Athletes. Med. Sci. Sports Exer. 2003, 35, 488–494. [Google Scholar] [CrossRef] [PubMed]
  70. Saltin, B.; Astrand, P.O. Maximal oxygen uptake in athletes. J. Appl. Physiol. 1967, 23, 353–358. [Google Scholar] [CrossRef] [PubMed]
  71. Tanaka, H.; Seals, D.R. Endurance exercise performance in Masters athletes: Age-associated changes and underlying physiological mechanisms. J. Physiol. 2008, 586, 55–63. [Google Scholar] [CrossRef] [PubMed]
  72. Maughan, R.J.; Burke, L.M.; Dvorak, J.; Larson-Meyer, D.E.; Peeling, P.E.; Phillips, S.M.; Rawson, E.S.; Walsh, N.P.; Garthe, I.; Geyer, H.; et al. IOC consensus statement: Dietary supplements and the high-performance athlete. Br. J. Sports Med. 2018, 52, 439–455. [Google Scholar] [CrossRef] [PubMed]
  73. Burke, D.G.; Chilibeck, P.D.; Parise, G.; Candow, D.G.; Mahoney, D.; Tarnopolsky, M. Effect of creatine and weight training on muscle creatine and performance in vegetarians. Med. Sci. Sports Exerc. 2003, 35, 1946–1955. [Google Scholar] [CrossRef]
  74. Stamler, J.S.; Singel, D.J.; Loscalzo, J. Biochemistry of nitric oxide and its redox-activated forms. Science 1992, 258, 1898–1902. [Google Scholar] [CrossRef]
  75. Freeman, B. Free radical chemistry of nitric oxide. Looking at the dark side. Chest 1994, 105, 79–84. [Google Scholar] [CrossRef]
  76. Kuchakulla, M.; Masterson, T.; Arora, H.; Kulandavelu, S.; Ramasamy, R. Effect of nitroso-redox imbalance on male reproduction. Transl. Urol. 2018, 7, 968–977. [Google Scholar] [CrossRef]
  77. Simon, J.N.; Ziberna, K.; Casadei, B. Compromised redox homeostasis, altered nitroso-redox balance, and therapeutic possibilities in atrial fibrillation. Cardiovasc. Res. 2016, 109, 510–518. [Google Scholar] [CrossRef]
  78. Gomez-Cabrera, M.C.; Domenech, E.; Romagnoli, M.; Arduini, A.; Borras, C.; Pallardo, F.V.; Sastre, J.; Viña, J. Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. Am. J. Clin. Nutr. 2008, 87, 142–149. [Google Scholar] [CrossRef] [PubMed]
  79. Morrison, D.; Hughes, J.; Della Gatta, P.A.; Mason, S.; Lamon, S.; Russell, A.P.; Wadley, G.D. Vitamin C and E supplementation prevents some of the cellular adaptations to endurance-training in humans. Free. Radic. Biol. Med. 2015, 89, 852–862. [Google Scholar] [CrossRef]
  80. Dutra, M.T.; Alex, S.; Silva, A.F.; Brown, L.E.; Bottaro, M. Antioxidant Supplementation Impairs Changes in Body Composition Induced by Strength Training in Young Women. Int. J. Exerc. Sci. 2019, 12, 287–296. [Google Scholar]
  81. Hoon, M.W.; Johnson, N.A.; Chapman, P.G.; Burke, L.M. The effect of nitrate supplementation on exercise performance in healthy individuals: A systematic review and meta-analysis. Int. J. Sport Nutr. Exerc. Metab. 2013, 23, 522–532. [Google Scholar] [CrossRef] [PubMed]
  82. Pawlak-Chaouch, M.; Boissière, J.; Gamelin, F.X.; Cuvelier, G.; Berthoin, S.; Aucouturier, J. Effect of dietary nitrate supplementation on metabolic rate during rest and exercise in human: A systematic review and a meta-analysis. Nitric Oxide. 2016, 53, 65–76. [Google Scholar] [CrossRef] [PubMed]
  83. McMahon, N.F.; Leveritt, M.D.; Pavey, T.G. The Effect of Dietary Nitrate Supplementation on Endurance Exercise Performance in Healthy Adults: A Systematic Review and Meta-Analysis. Sports Med. 2017, 47, 735–756. [Google Scholar] [CrossRef]
  84. Senefeld, J.W.; Wiggins, C.C.; Regimbal, R.J.; Dominelli, P.B.; Baker, S.E.; Joyner, M.J. Ergogenic Effect of Nitrate Supplementation: A Systematic Review and Meta-analysis. Med. Sci. Sports Exerc. 2020, 52, 2250–2261. [Google Scholar] [CrossRef]
  85. Jones, A.M. Influence of dietary nitrate on the physiological determinants of exercise performance: A critical review. Appl. Physiol. Nutr. Metab. 2014, 39, 1019–1028. [Google Scholar] [CrossRef]
  86. Laursen, P.B.; Francis, G.T.; Abbiss, C.R.; Newton, M.J.; Nosaka, K. Reliability of time-to-exhaustion versus time-trial running tests in runners. Med. Sci. Sports Exerc. 2007, 39, 1374–1379. [Google Scholar] [CrossRef] [PubMed]
  87. Fery, Y.A.; Ferry, A.; Hofe, A.V.; Rieu, M. Effect of Physical Exhaustion on Cognitive Functioning. Percept. Mot. Ski. 1997, 84, 291–298. [Google Scholar] [CrossRef] [PubMed]
  88. Thompson, C.; Wylie, L.J.; Fulford, J.; Kelly, J.; Black, M.I.; McDonagh, S.T.J.; Jeukendrup, A.E.; Vanhatalo, A.; Jones, A.M. Dietary nitrate improves sprint performance and cognitive function during prolonged intermittent exercise. Eur. J. Appl. Physiol. 2015, 115, 1825–1834. [Google Scholar] [CrossRef]
  89. Aamand, R.; Dalsgaard, T.; Ho, Y.C.L.; Møller, A.; Roepstorff, A.; Lund, T.E. A NO way to BOLD? Dietary nitrate alters the hemodynamic response to visual stimulation. Neuroimage 2013, 83, 397–407. [Google Scholar] [CrossRef] [PubMed]
  90. Haskell-Ramsay, C.; Thompson, K.; Jones, A.M.; Blackwell, J.R.; Winyard, P.G.; Forster, J.S. Nitrate-rich beetroot juice modulates cerebral blood flow and cognitive performance in humans. Appetite 2011, 57, 560. [Google Scholar] [CrossRef]
  91. Thompson, C.; Vanhatalo, A.; Jell, H.; Fulford, J.; Carter, J.; Nyman, L.; Bailey, S.J.; Jone, A.M. Dietary nitrate supplementation improves sprint and high-intensity intermittent running performance. Nitric Oxide 2016, 61, 55–61. [Google Scholar] [CrossRef] [PubMed]
  92. San Juan, A.F.; Dominguez, R.; Lago-Rodríguez, Á.; Montoya, J.J.; Tan, R.; Bailey, S.J. Effects of Dietary Nitrate Supplementation on Weightlifting Exercise Performance in Healthy Adults: A Systematic Review. Nutrients 2020, 12, 2227. [Google Scholar] [CrossRef]
  93. Shannon, O.M.; McGawley, K.; Nybäck, L.; Duckworth, L.; Barlow, M.J.; Woods, D.; Siervo, M.; O’Hara, J.P. “Beet-ing” the Mountain: A Review of the Physiological and Performance Effects of Dietary Nitrate Supplementation at Simulated and Terrestrial Altitude. Sports Med. 2017, 47, 2155–2169. [Google Scholar] [CrossRef] [PubMed]
  94. Van Mil, A.H.M.; Spilt, A.; Van Buchem, M.A.; Bollen, E.L.E.M.; Teppema, L.; Westendorp, R.G.J.; Blauw, G.J. Nitric oxide mediates hypoxia-induced cerebral vasodilation in humans. J. Appl. Physiol. 2002, 92, 962–966. [Google Scholar] [CrossRef]
  95. Diesen, D.L.; Hess, D.T.; Stamler, J.S. Hypoxic vasodilation by red blood cells: Evidence for an s-nitrosothiol-based signal. Circ. Res. 2008, 103, 545–553. [Google Scholar] [CrossRef]
  96. Martin, D.S.; Gilbert-Kawai, E.T.; Meale, P.M.; Fernandez, B.O.; Cobb, A.; Khosravi, M.; Mitchell, K.; Grocott, M.P.; Levett, D.Z.; Mythen, M.G.; et al. Xtreme Alps Research Group. Design and conduct of ‘Xtreme Alps’: A double-blind, randomised controlled study of the effects of dietary nitrate supplementation on acclimatisation to high altitude. Contemp. Clin. Trials 2013, 36, 450–459. [Google Scholar] [CrossRef]
  97. Cumpstey, A.F.; Hennis, P.J.; Gilbert-Kawai, E.T.; Fernandez, B.O.; Grant, D.; Jenner, W.; Poudevigne, M.; Moyses, H.; Levett, D.Z.; Cobb, A.; et al. Effects of dietary nitrate supplementation on microvascular physiology at 4559 m altitude—A randomised controlled trial (Xtreme Alps). Nitric Oxide. 2020, 94, 27–35. [Google Scholar] [CrossRef]
  98. Stellingwerff, T.; Peeling, P.; Garvican-Lewis, L.A.; Hall, R.; Koivisto, A.E.; Heikura, I.A.; Burke, L.M. Nutrition and Altitude: Strategies to Enhance Adaptation, Improve Performance and Maintain Health: A Narrative Review. Sports Med. 2019, 49, 169–184. [Google Scholar] [CrossRef]
  99. Salehzadeh, H.; Maleki, A.; Rezaee, R.; Shahmoradi, B.; Ponnet, K. The nitrate content of fresh and cooked vegetables and their health-related risks. PLoS ONE 2020, 15, e0227551. [Google Scholar] [CrossRef]
  100. Van der Avoort, C.M.T.; Van Loon, L.J.C.; Hopman, M.T.E.; Verdijk, L.B. Increasing vegetable intake to obtain the health promoting and ergogenic effects of dietary nitrate. Eur. J. Clin. Nutr. 2018, 72. [Google Scholar] [CrossRef]
  101. Walpurgis, K.; Thomas, A.; Geyer, H.; Mareck, U.; Thevis, M. Dietary Supplement and Food Contaminations and Their Implications for Doping Controls. Foods 2020, 9, 1012. [Google Scholar] [CrossRef] [PubMed]
Table 1. Effects of nitrate supplementation on exercise performance.
Table 1. Effects of nitrate supplementation on exercise performance.
Study (Year)Number of Participants (Sex)Participant Characteristics Supplementation ProtocolPerformance Protocol (Measured Variable)Main Findings
Larsen et al. (2007) [15]9 (7 M, 2 F)Cyclists and triathlon competitors (VO2peak 55 ± 3.7 mL/kg/min)0.033 mmol NO3/kg BM for 2 consecutive days thrice dailyIncremental ergometer test (time in s)↔ Time to exhaustion
Bailey et al. (2009) [16]8 (M)Healthy and recreationally active VO2max 49 ± 5 mL/kg/min)5.5 mmol NO3 for 6 consecutive daysHigh-intensity exercise (time in s)↓ O2 uptake during high-intensity exercise
↑ Time to exhaustion
↓ Systolic blood pressure
Bailey et al. (2010) [17]7 (M)Healthy and recreationally active 5.1 mmol NO3 for 6 consecutive days High-intensity exercise (time in s)↓ Muscle phosphocreatine degradation
↑ Time to exhaustion
↑ ATP turnover
Vanhatalo et al. (2010) [18]8 (5 M, 3 F)Healthy individuals 5.2 mmol NO3 twice daily for 15 consecutive days Incremental cycling test (power in W)↓ Steady-state VO2
↑ Peak power and work rate
Larsen et al. (2010) [32]9 (7 M, 2 F)Healthy and recreationally active (VO2max 3.72 ± 0.33 mL/kg/min)0.1 mmol NO3/kg BM for 2 consecutive days Incremental ergometer test (time in s)↔ Time to exhaustion
Vanhatalo et al. (2011) [33]9 (7 M, 2 F)Healthy and recreationally active 9.3 mmol NO3 split into three doses taken 24, 12, and 2.5 h prior to testingKnee extension (time in s)↑ Knee extension performance
↑ PCr recovery time constant
Lansley et al. (2011) [22]9 (M)Well-trained cyclists VO2peak 56 ± 5.7 mL/kg/min)≃6.2 mmol NO34 km and 16.1 km time trial (time in min and power in W)
↑ Power output in both 4 km and 16.1 km trial
↑ Performance in both 4 km and 16.1 km trial
Murphy et al. (2011) [23]11 (5 M, 6 F)Healthy and recreationally active 500 g beetroot (≃500 mg or 8 mmol NO3)5 km running time trial (velocity in km/h)↔ Performance
↓ RPE
Masschelein et al. (2012) [19]15 (M)Healthy and recreationally active (VO2peak 61.7± 2.1 mL/kg/min)0.07 mmol NO3/kg BM/day for 6 consecutive days Incremental ergometer test (time in s)↓ VO2 and ↑ arterial O2 saturation during rest and exercise in hypoxic conditions
Bescos et al. (2012) [34]13 (M)Cyclists and triathlon competitors 11.8 mmol NO3Incremental test (time in s and power in W)↔ Mean distance
↔ Power output
Peacock et al. (2012) [30]10 (M)Cross-country skiers (VO2max 69.6 ± 5.1 mL/kg/min)1 g KNO3 (9.9 mmol or 614 mg NO3)5 km running time trial (time in s)↔ Time trail performance
↔ O2 cost
Bond et al. (2012) [35]14 (M)Rowers5 mmol NO3 for 6 consecutive days 6 × 500 m ergometer test at high-intensity (time in s)↔ Rowing performance
Cermak et al. (2012) [36]12 (M)Cyclists and triathlon competitors (VO2peak = 58 ± 2 mL/kg/min; Wmax = 342 ± 10 W)8 mmol NO3 for 6 consecutive days 10 km running time trial (time in s and power in W)↑ Time trial performance
↑ Power output
Cermak et al. (2012) [25]20 (M)Cyclists and triathlon competitors (VO2peak 60 ± 1 mL/kg/min; Wmax 398 ± 7.7 W)8.7 mmol NO3Cycling at 75 % Wmax to ≃1073 kJ (caloric-expenditure-based time trial) (time in min and power in W)↔ Time trial
↔ Power output
↔ HR
Kelly et al. (2013) [37]9 (M)Healthy and recreationally active (VO2max 54.5 ± 7.5 mL/kg/min)8.2 mmol NO3 for 5 consecutive days Cyclic ergometry at 1) 60%, 2) 70%, 3) 80%, and 4) 100% Wmax (time in s)↑ Exercise tolerance at 60%, 70%, and 80% peak power
↔ At 100% peak power
Breese et al. (2013) [38]9 (4 M, 5 F)Healthy individuals 8 mmol NO3 for 6 consecutive days Incremental cycling test (time in s)↑ VO2 kinetics
↑ Time-to-task failure
Wylie et al. (2013) [39]10 (M)Healthy individuals (1) 4.2 or (2) 8.4 or (3) 16.8 mmol NO3Cycling to complete exhaustion (time in s) ↓ Steady-state O2 uptake during moderate-intensity exercise and ↑ time-to-task failure for 8.4 and 16.8 mmol NO3
Wylie et al. (2013) [40]14 (M)Team sports athletes (VO2max 52 ± 7 mL/kg/min)4.1 mmol NO3 twice daily for 2 consecutive days Yo-Yo test (distance in m)↑ Yo-Yo performance
Muggeridge et al. (2013) [20]8 (M)Kayak competitors (VO2max 49 ± 6.1 mL/kg/min)5.0 mmol NO315 min rowing at 60 % Wmax (power in W)↓ VO2
↔ Peak power or time trial performance
Christensen et al. (2013) [26]10 (M)Cyclists (VO2max 72 ± 4 mL/kg/min)5.0 mmol NO3 4 for 6 consecutive days Repeated sprints (power in W) and time trial ≃1677 kJ (energy-expenditure-based time trial) (time in s and power in W)↔ Vo2 kinetics
↔ Exercise economy
↔ Time trial performance
Hoon et al. (2014) [41]28 (M)Cyclists4.1 mmol NO34 min time trial (power in W)↔ Time trial performance
Boorsma et al. (2014) [42]8 (M)Elite 1500 m runners (VO2max 80 ± 5 mL/kg/min)19.5 mmol NO31500 m running time trial (time in s)↔ VO2peak
↔ Time trial performance
Martin et al. (2014) [43]16 (9 M, 7 F)Team sports athletes (VO2max M: 57.4 ± 8 mL/kg/min; F: 47.2 ± 8 mL/kg/min)4.83 mmol NO38 s repeated sprints test on cyclic ergometer (number of sprints, work in kJ, power in W) ↔ Mean power output
↓ Number of sprints
↓ Total work
Peeling et al. (2015) [44]6 (M)National-level kayak competitors (VO2peak 57.15 ± 2.8 mL/kg/min)5.5 mmol NO34 min maximal ergometer test (power in W and distance in m)↓ VO2
↑ Exercise economy
↑ Time trial performance
Porcelli et al. (2015) [21]21 (M)8 individuals with lower aerobic capacity (VO2peak 28.2–44.1 mL/kg/min), 7 individuals with medium aerobic capacity (VO2peak: 45.5–57.1 mL/kg/min), and 6 individuals with high aerobic capacity (VO2peak: 63.9–81.7 mL/kg/min)5.5 mmol NO3 for 5 consecutive days 3 km running time trial ↑ Time trial performance for lower and medium aerobic capacity
↔ Time trial performance for high aerobic capacity
Wylie et al. (2015) [45]10 (M)Healthy and recreationally active 8.2 mmol NO3 3, 4 or 5 consecutive days 24 × 6 s sprints with 24 s rest; 7 × 30 s sprints with 240 s rest; 6 × 60 s sprints with 60 s rest (power in W)↑ Power output for condition 1
↔ Power output for conditions 2 and 3
McQuillan et al. (2017a) [27]9 (M)Cyclists (VO2peak: 68 ± 3 mL/kg/min)9 mmol NO3 3 for 7 consecutive days 1 km time trial at fourth and seventh day of investigation and 4 km time trial at third in sixth day of investigation (time in s and power in W)↔ Time trial
↔ Power output
McQuillan et al. (2017b) [28]8 (M)Cyclists (VO2peak = 63 ± 4 mL/kg/min)~4 mmol NO3 for 8 consecutive days 4 km time trial (time in s in power in W)↔ Time trial
↔ Power output
Christensen et al. (2017) [46]17 (M)8 recreationally active (VO2max 46 ± 3 mL/kg/min) and 9 well-trained cyclists (VO2max: 64 ± 3 mL/kg/min) 9 mmol NO3Incremental test for cycling
and arm cranking (power in W)
↔VO2max
↑ Peak power for cycling
↔ Peak power for arm cranking
Nyakayiru et al. (2017a) [29]17 (M)Cyclists and triathlon competitors (65 ± 4 mL/kg/min, Wmax 411 ± 35 W)4 mmol NO3 for 6 consecutive days 10 km time trial (time in s)↔VO2
↔ Time trial
Nyakayiru et al. (2017b) [24]32 (M)Football players12.9 mmol NO3 for 6 consecutive days Yo-Yo test (distance in m)↑ Covered distance
Vasconcellos et al. (2017) [47]25 (14 M, 11 F)Runners (M: VO2peak 64.31 ± 4.71 mL/kg/min−1; F: VO2peak 52.79 ± 4.57 mL/kg/min9.92 NO3 ± 1,97 mmolHigh-intensity running (time in s)↔ Time to fatigue
↔ VO2max
↓ Blood glucose
↔ Systolic and diastolic blood pressures
↔ Serum cortisol,
↔ Blood lactate
Shannon et al. (2017) [48]8 (M)Runners in triathlon competitors (VO2max: 62.3 ± 8.1 mL/kg/min)~12.5 mmol NO3Running for 1500 m and 10 000 m (time in s)↔ Resting blood pressure
↑ Blood lactate for 1500 m time trial
↔ Blood lactate for 10,000 m time trial
↑ Time trial performance for 1500 m
↔ Time trial performance for 10,000 m
De Castro et al. (2018) [49]14 (M)Healthy and recreationally active runners (VO2max: 45.4 ± 5.9 mL/kg/min)8.4 mmol NO3 for 3 consecutive days 10 km running time trial (time in min and velocity in km/h)↔ Time trial performance
↔ Mean velocity
Cuenca et al. (2018) [50]15 (M)Healthy and recreationally active6.4 mmol NO3WAnT and CMJ (power in W, time to Wpeak)↑ Peak and mean power output
↓ Time taken to reach Wpeak
Oskarsson et al. (2018) [51]9 (M 7, F 2)(M: VO2max 59.0 ± 2.9 mL/kg/min; F: VO2max 53.1 ± 11.4 mL/kg/min) 6.4 mmol NO31 km running time trial (time in s)↔ Relative oxygen uptake, running economy, respiratory exchange ratio, HR, or RPE at submaximal intensities
↔ Performance, maximum HR, peak blood lactate concentration, or RPE during the maximal-intensity time trial
Jo et al. (2019) [52]29 (M 15, F 14)Healthy and recreationally active 8 mmol NO3 for 15 consecutive days 8 km time trial (time in s, power in W, velocity in km/h)Multiday NO3 supplementation:
↑ Time trial performance
↑ Average power
↑ Velocity
Single serving NO3:
↔ Time trial performance
↔Average power
↔ Velocity
Rokkedal-Lausch et al. (2019) [53]12 (M)Cyclists (VO2max 66.4 ± 5.3 mL/min/kg)12.4 mmol NO3 for 7 consecutive days 10 km time trial in normoxic and hypoxic conditions (time in s and power in W)↑ Time trial performance in normoxic and hypoxic conditions
↔ HR
↔ Oxygen saturation
↔ Muscle oxygenation
Esen et al. (2019) [54]10 (5 M, 5 F)Swimmers with a minimum of 10 years training experience and minimum of 5 years competing experience~800 mg NO3 for 3 consecutive days 100 in 200 m swimming for time (time in s)↔ Time trial performance for 100 and 200 m
↓ Systolic blood pressure
Wickham et al. (2019) [55]12 (F)Healthy and recreationally active (VO2peak: 40.7 ± 4.3 mL/kg/min)Acute and chronic supplementation (~26 mmol) of NO3 for either 1 or 8 consecutive days10 min time trial at 50 and 70 % VO2max (time in s)↔ MVC voluntary activation
↔ Peak twitch torque, ↔ time to peak torque, ↔ half relaxation time
↔ Time trial performance
↔ VO2
Kent et al. (2019) [56]12 (M)Team sports athletes (VO2peak 53.1 ± 8.7 mL/kg/min)12.9 mmol NO3Four cycling sprints at sea and 3000 m altitude↔ Peak and mean power
Mosher et al. (2019) [57]11 (M)Cyclists (VO2max: 60.8 ± 7.4 mL/kg/min)12.8 mmol NO3 for 3 consecutive days 40 km time trial (time in s)↔ Time trial performance
↔ VO2
↔ Blood lactate
↔ RPE
Ranchal-Sanchez et al. (2020) [58]12 (M)Healthy and recreationally active 6.4 mmol NO3Incremental test at 60, 70, and 80% maximal power for bench press and squat (number of repetitions, power in W, and velocity in m/s)↑ NOR for 60 and 70% 1 RM
↔ NOR for 80% 1 RM
↑ NOR for squat
↔ NOR for bench press
↔ Power
↔ Velocity
López-Samanes et al. (2020) [59]13 (M)Professional tennis players300 mg NO3Serving speed, CMJ, IHS, 5-0-5 agility test, and 10 m sprints test↔ Serve velocity
↔ CMJ
↔ IHS
↔ 5-0-5 agility test
↔ Sprint performance
Liubertas et al. (2020) [60]13 (M)Healthy individuals Acute and chronic intake (for 6 consecutive days) of 400 mg NO3Incremental cycling test first, third, and sixth day of investigation (power in W and VO2max) ↑ Peak power
↑ VO2max
Rodríguez-Fernández et al. (2020) [61]18 (M)Healthy and recreationally active 800 mg NO3Four sets of eight all-out half-squats with each set completed at different moment intertia (power in W)↑ Mean and peak power output in the concentric and eccentric movement phases
Jonvik et al. (2021) [62]15 (M)Recreationally active985 mg NO3 for 6 consecutive daysCMJ, upper leg voluntary isometric (30° and 60° angle) and isokinetic contractions (60, 120, 180, and 300°s−1) and test of 30 reciprocal isokinetic voluntary contractions at 180°s−1↔ CMJ
↔ Maximal isometric knee extensor strength and isokinetic knee extension power
↔ Muscular endurance
Dumar et al. (2021) [63] 10 (M)National Collegiate Athletic Association sprinters400 mg NO3 2 h prior to exercise3 × 15 s WAnT with 2 min rest in the AM and PM (power in W and anaerobic capacity in Wkg−1)NO3 attenuated the decrease in AM exercise performance
↔ RPE
↓ HR
Marshall et al. (2021) [64]22 (12 M, 10 W)Healthy adults~12.5 mmol NO3 for 20 consecutive daysHarvard Step Test fitness at baseline (44 m altitude), 2350 m (day 9), 3400 m (day 12), and 4800 m (day 17)NO3 attenuated the decline in fitness scores with altitude
↑ HR recovery
↔ RPE
↔ High-altitude illness occurrence
Fowler et al. (2021) [65]11 (M)Healthy adults (VO2max: 41.1 ± 3.6 mL/kg/min)∼9.2 mmol NO3 for 5 consecutive daysCycling exercise tolerance test in hot and dry conditions (35 °C, 28% relative humidity)↔ Performance
↓ Arterial pressure
↔ Sweat rate
↔ Heart rate
↔ Oxygen consumption and carbon dioxide production
↔ Thermal sensation
Townsend et al. (2021) [66]16 (M)Division I baseball athletes180 mg NO3 daily for 11 weeks1 RM bench press, WAnT, body composition analysis via a 4-compartment model↔Perfromance (1 RM bench press and WAnT; observed trend for improved peak power in the WAnT)
↔ Body composition and muscle thickness
↔ HR and blood pressure
↑ = Significantly greater (p < 0.05) compared with placebo; ↔ = no significant change compared with placebo; ↓ = significantly lower (p < 0.05) compared with placebo; NO3 = nitrates; BM = body mass; PCr = phosphocreatine; RPE = rating of perceived exertion; WAnT = Wingate anaerobic test; CMJ = counter movement jump; HR = heart rate; MVC = maximum voluntary strength; NOR = number of repetitions; 1 RM = repetition maximum; HIS = isometric grip strength. Potential reasons why some studies presented in Table 1 report a positive effect of NO3 supplementation and others do not may result from different research methodological approaches, different testing, and supplementation protocols, potentially through the production of free radicals through NO reaction with O2, and differences between participants training status. The latter may be the most prominent reason why researchers report different findings, and many factors may contribute to this effect. The first is that intense exercise itself increases NOS activity [67], making top-tier athletes less dependent on the NO3–NO2–NO pathway of NO production and having higher baseline levels of NO3 in comparison to less trained individuals [4]. Poveda et al. (1997) reported a 158% increase in baseline plasma NO2 concentration in a sample of 10 well-trained runners and cyclists versus non-trained individuals [68]. Porcelli et al. (2015) reported that when VO2max is low (<65 mL/kg/min), the effect of NO3 on reducing oxygen consumption during exercise is most pronounced and can be as high as 10%. On the other hand, at higher VO2max (>65 mL/kg/min), the effect of NO3 is negligible [21]. It is worth noting that VO2max is affected by both sports’ specificity as well as age. Certain elite-level athletes where NO3 supplementation might be useful participating in sports requiring not only endurance, but also speed, strength, and anaerobic capacity might not have the same level of VO2max as solely endurance athletes [69,70]. Additionally, in master athletes, there is a progressive decline of VO2max with age [71]. Thus, a specific cut-off point at 65 mL/kg/min justifying the usage of NO3 supplementation might or not might not be valid in all sports situations.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Back to TopTop