Supplement Review: Dietary Nitrate and Beetroot Juice

In the human body, Nitric Oxide (NO) promotes vasodilation, or widening of the blood vessels, which increases blood flow and reduces blood pressure [1-3]. NO is heavily involved with many physiological processes that affect exercise performance, including the regulation of blood flow, skeletal muscle contraction, and mitochondrial respiration and biogenesis [3-5].

Note: You may have noticed that a few words are highlighted in blue; abbreviations for these words are used extensively in this article.

Through these mechanisms, NO can enhance exercise performance via improved function of type II (fast-twitch) muscle fibers [6], reduced ATP (energy) cost of muscle force production [7], increased efficiency of mitochondrial respiration [3], and increased blood flow (and thus delivery of oxygen and nutrients) to the muscles active during exercise [1, 7].

Nitrate

Dietary Nitrate and Endurance Exercise Performance

There’s a substantial body of evidence that shows dietary nitrate supplementation can improve endurance exercise performance. For example, oxygen efficiency during submaximal exercise [8-10], time-to-exhaustion [10-12] and time trial performances [13-16] have all been improved with dietary nitrate supplementation. A recent meta-analysis and systematic review of the literature supports these performance enhancements [17].

Endurance performances lasting ~12-40 minutes are generally enhanced by dietary nitrate supplementation [8-19, 43]. Research supporting ergogenicity for exercise tasks lasting <12 minutes is inconclusive [20-25], and exercise performance lasting >40 minutes is not supported [26-29]. In World-Class, short-track speed skaters, 1000-m time trial performance lasting ~90 seconds was not enhanced with chronic dietary nitrate supplementation [20]. Similarly, 4-km and 168-m performances by elite cyclists and trained swimmers, respectively, were not enhanced [21, 22]. On the other hand, dietary nitrate supplementation improved 1,500-m and 4-km time trial performances in trained runners [18] and competitive cyclists [19], respectively. Differences in supplementation timing and dosing are likely contributors to these mixed outcomes [30, 31].

DN2.jpg

Dietary Nitrate and Intermittent High-Intensity Performance

More recently, research has focused on the potential for dietary nitrate to enhance performance in repeated high-intensity tasks, which is a physiological requirement for many team sports. Many different intermittent high-intensity protocols in various cohorts, ranging from untrained to elite team-sport athletes, have been investigated [32-39]. When dietary nitrate was consumed throughout 3 weeks of sprint interval training, maximal work rate during an incremental graded cycling test was enhanced, compared with placebo, in untrained males [34]. In high-level soccer players, 6 days of beetroot juice (i.e. dietary nitrate) supplementation improved performance on a Yo-Yo IR1 test (i.e. intermittent high-intensity running), compared with placebo [38]. Similarly, 5 days of beetroot juice intake was associated with sprint speed and Yo-Yo IR1 test performance improvements in football, rugby, and hockey athletes [36]. In recreational cyclists, national talent speed-skaters, and Olympic-level track cyclists, 6 days of beetroot juice intake reduced time to reach peak power in a 30-second all-out cycling sprint (Wingate), regardless of sport and level [32].

Nitrate 2

A recent review of the literature concluded that supplementation with beetroot juice, a common source of dietary nitrate, improves intermittent high-intensity performance, likely due to accelerated phosphocreatine (PCr) resynthesis and faster muscle shortening velocity [40]. The former would delay the PCr depletion during repeated high-intensity exercise efforts and the latter would improve muscle power output [40].

The Impact of Training Status

Training status may impact ergogenicity of nitrate supplementation [30, 41, 42], with highly trained athletes requiring higher intakes to reap performance benefits [30, 41], but this is not always true [15, 18, 34]. Overall, more research is needed to determine if and how training status impacts dietary nitrate supplementation ergogenicity.

The IOC Recommendation

Recently, beetroot juice has become a suggested, evidence-based approach to enhance athletic performance [43]. In fact, it’s one of the few supplements that the International Olympic Committee (IOC) recommends for the high-performance athlete [44].

Dietary Sources, Dosing, and Safety

Leafy green and root vegetables, including spinach, rocket salad, celery, and beetroot, are foods that contain high levels of nitrate [44]. Beetroot is perhaps the most popular for supplementation, likely due to its 100% bioavailability [49].

Acute performance benefits are generally observed 2-3 hours following ingestion [14, 45, 46]. Hoon et al. (2014) reported such benefits following 5-9 mmol of dietary nitrate intake [14]. However, it must be noted that substantial inter-individual differences in these pharmacokinetics can exist, resulting in varying optimal doses and timings for supplementation [47]. In other words, the dosage and timing that’s advised in the research may not be optimal for you or me. With that being said, 5-9 mmol seems to be the most effective dose for performance benefit, in most people [17]. However, high-level athletes may require greater intakes [7, 30, 48], perhaps between 9-11 mmol [48].

These quantities can easily be met through consumption of vegetables rich in dietary nitrate (i.e. beetroot, spinach, and rocket/rogula), but there doesn’t appear to be anything wrong with supplementary products. In general, there appears to be few, if any, side effects with nitrate supplementation in doses suggested in literature [43]. Some athletes may experience gastrointestinal (GI) upset, and thus, high dietary nitrate intakes and/or supplementation should be trialed during training, as opposed to competition [43].

Other Nitric Oxide (NO) Promoters: L-Arginine and L-Citrulline

L-arginine and L-citrulline supplementation can increase nitric oxide (NO) metabolites, but this don’t necessarily translate to increased NO in the body, or exercise performance benefits [50, 51]. Although one small study showed improved moderate-intensity exercise performance after acute 6g L-Arginine supplementation consumed pre-exercise [52], the majority of other L-arginine supplementation protocols resulted in no cardiovascular exercise performance benefit [53-58].

There’s less research on L-citrulline than L-arginine. Although there are multiple reports that indicate L-citrulline is more likely to benefit exercise performance than L-arginine [59-64], the research on L-citrulline ergogenicity is inconsistent and inconclusive, at this time [50, 64-66]. Like L-arginine, L-citrulline should not be recommended as an ergogenic aid because there is not enough research, currently, to support its efficacy.

Summary

Overall, dietary nitrate appears to be beneficial for endurance and intermittent high-intensity performance lasting 12-40 minutes, but not for performances of shorter [20-23, 43], or longer duration [26-29]. Foods high in dietary nitrate include leafy green and root vegetables, such as beets, radishes, turnips, lettuce, and spinach. Although 5-9 mmol seems like an appropriate dosage for most people [4, 17], it appears that athletes need higher intakes to experience exercise benefits. Overall, more research is needed to determine optimal dosing strategies.

The evidence on exercise performance ergogenicity when using other Nitric Oxide (NO) enhancers, such as L-arginine and L-citrulline, is less clear. L-arginine appears to offer no cardiovascular exercise performance benefit [53-58]. While L-citrulline is more likely to offer ergogenicity, reports have been inconsistent to-date [50, 59-66]. Research does not currently support supplementation with L-arginine or L-citrulline for improved cardiovascular exercise performance.

Reference:

  1. Besco R, Sureda A, Tur JA, Pons A. The effect of nitric-oxide-related supplements on human performance. Sports medicine. 2012 Feb 1;42(2):99-117.
  2. Lundberg, J.O., Weitzberg, E., Shiva, S. and Gladwin, M.T., 2011. The nitrate–nitrite–nitric oxide pathway in mammals. In Nitrite and nitrate in human health and disease (pp. 21-48). Humana Press.
  3. Larsen, F.J., Schiffer, T.A., Borniquel, S., Sahlin, K., Ekblom, B., Lundberg, J.O. and Weitzberg, E., 2011. Dietary inorganic nitrate improves mitochondrial efficiency in humans. Cell metabolism, 13(2), pp.149-159.
  4. Stamler, J.S. and Meissner, G., 2001. Physiology of nitric oxide in skeletal muscle. Physiological reviews, 81(1), pp.209-237.
  5. Shen, W., Xu, X., Ochoa, M., Zhao, G., Wolin, M.S. and Hintze, T.H., 1994. Role of nitric oxide in the regulation of oxygen consumption in conscious dogs. Circulation Research, 75(6), pp.1086-1095.
  6. Bailey, S.J., Varnham, R.L., DiMenna, F.J., Breese, B.C., Wylie, L.J. and Jones, A.M., 2015. Inorganic nitrate supplementation improves muscle oxygenation, O2 uptake kinetics, and exercise tolerance at high but not low pedal rates. Journal of applied physiology, 118(11), pp.1396-1405.
  7. Jones, A.M., 2014. Influence of dietary nitrate on the physiological determinants of exercise performance: a critical review. Applied Physiology, Nutrition, and Metabolism, 39(9), pp.1019-1028.
  8. Larsen, F.J., Weitzberg, E., Lundberg, J.O. and Ekblom, B., 2007. Effects of dietary nitrate on oxygen cost during exercise. Acta physiologica, 191(1), pp.59-66.
  9. Vanhatalo, A., Bailey, S.J., Blackwell, J.R., DiMenna, F.J., Pavey, T.G., Wilkerson, D.P., Benjamin, N., Winyard, P.G. and Jones, A.M., 2010. Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 299(4), pp.R1121-R1131.
  10. Bailey, S.J., Winyard, P., Vanhatalo, A., Blackwell, J.R., DiMenna, F.J., Wilkerson, D.P., Tarr, J., Benjamin, N. and Jones, A.M., 2009. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. Journal of applied physiology, 107(4), pp.1144-1155.
  11. Breese, B.C., McNarry, M.A., Marwood, S., Blackwell, J.R., Bailey, S.J. and Jones, A.M., 2013. Beetroot juice supplementation speeds O2 uptake kinetics and improves exercise tolerance during severe-intensity exercise initiated from an elevated metabolic rate. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 305(12), pp.R1441-R1450.
  12. Kelly, J., Vanhatalo, A., Wilkerson, D.P., Wylie, L.J. and Jones, A.M., 2013. Effects of nitrate on the power-duration relationship for severe-intensity exercise. Med Sci Sports Exerc, 45(9), pp.1798-806.
  13. Cermak, N.M., Gibala, M.J. and Van Loon, L.J., 2012. Nitrate supplementation’s improvement of 10-km time-trial performance in trained cyclists. International journal of sport nutrition and exercise metabolism, 22(1), pp.64-71.
  14. Hoon, M.W., Jones, A.M., Johnson, N.A., Blackwell, J.R., Broad, E.M., Lundy, B., Rice, A.J. and Burke, L.M., 2014. The effect of variable doses of inorganic nitrate-rich beetroot juice on simulated 2000-m rowing performance in trained athletes. International journal of sports physiology and performance, 9(4), pp.615-620.
  15. McMahon, N.F., Leveritt, M.D. and Pavey, T.G., 2017. The effect of dietary nitrate supplementation on endurance exercise performance in healthy adults: a systematic review and meta-analysis. Sports medicine, 47(4), pp.735-756.
  16. McQuillan, J.A., Dulson, D.K., Laursen, P.B. and Kilding, A.E., 2017. The effect of dietary nitrate supplementation on physiology and performance in trained cyclists. International journal of sports physiology and performance, 12(5), pp.684-689.
  17. Van De Walle, G.P. and Vukovich, M.D., 2018. The Effect of Nitrate Supplementation on Exercise Tolerance and Performance: A Systematic Review and Meta-Analysis. The Journal of Strength & Conditioning Research, 32(6), pp.1796-1808.
  18. Shannon OM, Barlow MJ, Duckworth L, Williams E, Wort G, Woods D, Siervo M, O’Hara JP. Dietary nitrate supplementation enhances short but not longer duration running time-trial performance. European journal of applied physiology. 2017 Apr 1;117(4):775-85.
  19. Lansley, K.E., Winyard, P.G., Bailey, S.J., Vanhatalo, A., Wilkerson, D.P., Blackwell, J.R., Gilchrist, M., Benjamin, N. and Jones, A.M., 2011. Acute dietary nitrate supplementation improves cycling time trial performance. Medicine & Science in Sports & Exercise, 43(6), pp.1125-1131.
  20. Richard, P., Koziris, L.P., Charbonneau, M., Naulleau, C., Tremblay, J. and Billaut, F., 2018. Time-trial Performance in World-Class Speed Skaters After Chronic Nitrate Ingestion. International journal of sports physiology and performance, pp.1-22.
  21. Lowings, S., Shannon, O.M., Deighton, K., Matu, J. and Barlow, M.J., 2017. Effect of dietary nitrate supplementation on swimming performance in trained swimmers. International journal of sport nutrition and exercise metabolism, 27(4), pp.377-384.
  22. McQuillan, J.A., Casadio, J.R., Dulson, D.K., Laursen, P.B. and Kilding, A.E., 2018. The effect of nitrate supplementation on cycling performance in the heat in well-trained cyclists. International journal of sports physiology and performance, 13(1), pp.50-56.
  23. Reynolds, C.M.E., Halpenny, C., Hughes, C., Jordan, S., Quinn, A. and Egan, B., 2016. Acute ingestion of beetroot juice does not improve repeated sprint performance in male team sport athletes. The Proceedings of the Nutrition Society, 75(OCE3).
  24. McQuillan, J.A., Dulson, D.K., Laursen, P.B. and Kilding, A.E., 2017. Dietary nitrate fails to improve 1 and 4 km cycling performance in highly trained cyclists. International journal of sport nutrition and exercise metabolism, 27(3), pp.255-263.
  25. Nyakayiru, J.M., Jonvik, K.L., Pinckaers, P.J., Senden, J., van Loon, L.J. and Verdijk, L.B., 2017. No effect of acute and 6-day nitrate supplementation on V̇o2 and time-trial performance in highly trained cyclists. International journal of sport nutrition and exercise metabolism, 27(1), pp.11-17.
  26. Cermak NM, Res P, Stinkens R, et al. No improvement in endurance performance following a single dose of beetroot juice. Int J Sport Nutr Exerc Metab. 2012;22:470–8.
  27. Wilkerson DP, Hayward GM, Bailey SJ, et al. Influence of acute dietary nitrate supplementation on 50 mile time trial performance in well-trained cyclists. Eur J Appl Physiol. 2012;112:4127–34.
  28. Bescós R, Ferrer-Roca V, Galilea PA, et al. Sodium nitrate supplementation does not enhance performance of endurance athletes. Med Sci Sports Exerc. 2012;44:2400–9.
  29. Jones, A.M., 2014. Dietary nitrate supplementation and exercise performance. Sports medicine, 44(1), pp.35-45.
  30. Domínguez, R., Cuenca, E., Maté-Muñoz, J.L., García-Fernández, P., Serra-Paya, N., Estevan, M.C.L., Herreros, P.V. and Garnacho-Castaño, M.V., 2017. Effects of beetroot juice supplementation on cardiorespiratory endurance in athletes. A systematic review. Nutrients, 9(1), p.43.
  31. Casazza, G.A., Tovar, A.P., Richardson, C.E., Cortez, A.N. and Davis, B.A., 2018. Energy Availability, Macronutrient Intake, and Nutritional Supplementation for Improving Exercise Performance in Endurance Athletes. Current sports medicine reports, 17(6), pp.215-223.
  32. Jonvik, K.L., Nyakayiru, J., Van Dijk, J.W., Maase, K., Ballak, S.B., Senden, J.M.G., Van Loon, L.J.C. and Verdijk, L.B., 2018. Repeated-sprint performance and plasma responses following beetroot juice supplementation do not differ between recreational, competitive and elite sprint athletes. European journal of sport science, 18(4), pp.524-533.
  33. Wylie, L.J., Bailey, S.J., Kelly, J., Blackwell, J.R., Vanhatalo, A. and Jones, A.M., 2016. Influence of beetroot juice supplementation on intermittent exercise performance. European journal of applied physiology, 116(2), pp.415-425.
  34. Muggeridge, D.J., Sculthorpe, N., James, P.E. and Easton, C., 2017. The effects of dietary nitrate supplementation on the adaptations to sprint interval training in previously untrained males. Journal of science and medicine in sport, 20(1), pp.92-97.
  35. Thompson, C., Wylie, L.J., Fulford, J., Kelly, J., Black, M.I., McDonagh, S.T., Jeukendrup, A.E., Vanhatalo, A. and Jones, A.M., 2015. Dietary nitrate improves sprint performance and cognitive function during prolonged intermittent exercise. European journal of applied physiology, 115(9), pp.1825-1834.
  36. Thompson, C., Vanhatalo, A., Jell, H., Fulford, J., Carter, J., Nyman, L., Bailey, S.J. and Jones, A.M., 2016. Dietary nitrate supplementation improves sprint and high-intensity intermittent running performance. Nitric Oxide, 61, pp.55-61.
  37. Wylie, L.J., Mohr, M., Krustrup, P., Jackman, S.R., Ermιdis, G., Kelly, J., Black, M.I., Bailey, S.J., Vanhatalo, A. and Jones, A.M., 2013. Dietary nitrate supplementation improves team sport-specific intense intermittent exercise performance. European journal of applied physiology, 113(7), pp.1673-1684.
  38. Nyakayiru, J., Jonvik, K.L., Trommelen, J., Pinckaers, P.J., Senden, J.M., van Loon, L.J. and Verdijk, L.B., 2017. Beetroot juice supplementation improves high-intensity intermittent type exercise performance in trained soccer players. Nutrients, 9(3), p.314.
  39. Bond, H., Morton, L. and Braakhuis, A.J., 2012. Dietary nitrate supplementation improves rowing performance in well-trained rowers. International journal of sport nutrition and exercise metabolism, 22(4), pp.251-256.
  40. Domínguez, R., Maté-Muñoz, J.L., Cuenca, E., García-Fernández, P., Mata-Ordoñez, F., Lozano-Estevan, M.C., Veiga-Herreros, P., da Silva, S.F. and Garnacho-Castaño, M.V., 2018. Effects of beetroot juice supplementation on intermittent high-intensity exercise efforts. Journal of the International Society of Sports Nutrition, 15(1), p.2.
  41. James, P.E., Willis, G.R., Allen, J.D., Winyard, P.G. and Jones, A.M., 2015. Nitrate pharmacokinetics: Taking note of the difference. Nitric Oxide, 48, pp.44-50.
  42. Peeling, P., Cox, G.R., Bullock, N. and Burke, L.M., 2015. Beetroot juice improves on-water 500 m time-trial performance, and laboratory-based paddling economy in national and international-level kayak athletes. International journal of sport nutrition and exercise metabolism, 25(3), pp.278-284.
  43. Peeling, P., Binnie, M.J., Goods, P.S., Sim, M. and Burke, L.M., 2018. Evidence-based supplements for the enhancement of athletic performance. International journal of sport nutrition and exercise metabolism, 28(2), pp.178-187.
  44. Maughan, R.J., Burke, L.M., Dvorak, J., Larson-Meyer, D.E., Peeling, P., Phillips, S.M., Rawson, E.S., Walsh, N.P., Garthe, I., Geyer, H. and Meeusen, R., 2018. IOC consensus statement: dietary supplements and the high-performance athlete. International journal of sport nutrition and exercise metabolism, 28(2), pp.104-125.
  45. Webb, A.J., Patel, N., Loukogeorgakis, S., Okorie, M., Aboud, Z., Misra, S., Rashid, R., Miall, P., Deanfield, J., Benjamin, N. and MacAllister, R., 2008. Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite. Hypertension, 51(3), pp.784-790.
  46. Vanhatalo, A., Bailey, S.J., Blackwell, J.R., DiMenna, F.J., Pavey, T.G., Wilkerson, D.P., Benjamin, N., Winyard, P.G. and Jones, A.M., 2010. Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 299(4), pp.R1121-R1131.
  47. McIlvenna, L.C., Monaghan, C., Liddle, L., Fernandez, B.O., Feelisch, M., Muggeridge, D.J. and Easton, C., 2017. Beetroot juice versus chard gel: A pharmacokinetic and pharmacodynamic comparison of nitrate bioavailability. Nitric Oxide, 64, pp.61-67.
  48. Peeling, P., Cox, G.R., Bullock, N. and Burke, L.M., 2015. Beetroot juice improves on-water 500 m time-trial performance, and laboratory-based paddling economy in national and international-level kayak athletes. International journal of sport nutrition and exercise metabolism, 25(3), pp.278-284.
  49. Van Velzen, A.G., Sips, A.J., Schothorst, R.C., Lambers, A.C. and Meulenbelt, J., 2008. The oral bioavailability of nitrate from nitrate-rich vegetables in humans. Toxicology letters, 181(3), pp.177-181.
  50. Sureda, A. and Pons, A., 2012. Arginine and citrulline supplementation in sports and exercise: ergogenic nutrients?. In Acute Topics in Sport Nutrition (Vol. 59, pp. 18-28). Karger Publishers.
  51. Brooks, J.R., Oketch-Rabah, H., Low Dog, T., Gorecki, D.K., Barrett, M.L., Cantilena, L., Chung, M., Costello, R.B., Dwyer, J., Hardy, M.L. and Jordan, S.A., 2016. Safety and performance benefits of arginine supplements for military personnel: a systematic review. Nutrition reviews, 74(11), pp.708-721.
  52. Bailey, S.J., Winyard, P.G., Vanhatalo, A., Blackwell, J.R., DiMenna, F.J., Wilkerson, D.P. and Jones, A.M., 2010. Acute L-arginine supplementation reduces the O2 cost of moderate-intensity exercise and enhances high-intensity exercise tolerance. Journal of Applied Physiology, 109(5), pp.1394-1403.
  53. Alvares, T.S., Conte-Junior, C.A., Silva, J.T. and Paschoalin, V.M.F., 2014. L-arginine does not improve biochemical and hormonal response in trained runners after 4 weeks of supplementation. Nutrition Research, 34(1), pp.31-39.
  54. Bescós, R., Gonzalez-Haro, C., Pujol, P., Drobnic, F., Alonso, E., Santolaria, M.L., Ruiz, O., Esteve, M. and Galilea, P., 2009. Effects of dietary L-arginine intake on cardiorespiratory and metabolic adaptation in athletes. International journal of sport nutrition and exercise metabolism, 19(4), pp.355-365.
  55. Schaefer, A., Piquard, F., Geny, B., Doutreleau, S., Lampert, E., Mettauer, B. and Lonsdorfer, J., 2002. L-arginine reduces exercise-induced increase in plasma lactate and ammonia. International journal of sports medicine, 23(06), pp.403-407.
  56. Liu, T.H., Wu, C.L., Chiang, C.W., Lo, Y.W., Tseng, H.F. and Chang, C.K., 2009. No effect of short-term arginine supplementation on nitric oxide production, metabolism and performance in intermittent exercise in athletes. The Journal of nutritional biochemistry, 20(6), pp.462-468.
  57. Willoughby, D.S., Boucher, T., Reid, J., Skelton, G. and Clark, M., 2011. Effects of 7 days of arginine-alpha-ketoglutarate supplementation on blood flow, plasma L-arginine, nitric oxide metabolites, and asymmetric dimethyl arginine after resistance exercise. International journal of sport nutrition and exercise metabolism, 21(4), pp.291-299.
  58. Abel, T., Knechtle, B., Perret, C., Eser, P., Von Arx, P. and Knecht, H., 2005. Influence of chronic supplementation of arginine aspartate in endurance athletes on performance and substrate metabolism. International journal of sports medicine, 26(05), pp.344-349.
  59. Schwedhelm, E., Maas, R., Freese, R., Jung, D., Lukacs, Z., Jambrecina, A., Spickler, W., Schulze, F. and Böger, R.H., 2008. Pharmacokinetic and pharmacodynamic properties of oral L‐citrulline and L‐arginine: impact on nitric oxide metabolism. British journal of clinical pharmacology, 65(1), pp.51-59.
  60. Sureda, A., Córdova, A., Ferrer, M.D., Pérez, G., Tur, J.A. and Pons, A., 2010. L-citrulline-malate influence over branched chain amino acid utilization during exercise. European journal of applied physiology, 110(2), pp.341-351.
  61. Bailey, S.J., Blackwell, J.R., Lord, T., Vanhatalo, A., Winyard, P.G. and Jones, A.M., 2015. L-citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. Journal of Applied Physiology, 119(4), pp.385-395.
  62. Suzuki, T., Morita, M., Kobayashi, Y. and Kamimura, A., 2016. Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study. Journal of the International Society of Sports Nutrition, 13(1), p.6.
  63. Glenn, J.M., Gray, M., Jensen, A., Stone, M.S. and Vincenzo, J.L., 2016. Acute citrulline-malate supplementation improves maximal strength and anaerobic power in female, masters athletes tennis players. European journal of sport science, 16(8), pp.1095-1103.
  64. Figueroa, A., Wong, A., Jaime, S.J. and Gonzales, J.U., 2017. Influence of L-citrulline and watermelon supplementation on vascular function and exercise performance. Current Opinion in Clinical Nutrition & Metabolic Care, 20(1), pp.92-98.
  65. Cutrufello, P.T., Gadomski, S.J. and Zavorsky, G.S., 2015. The effect of l-citrulline and watermelon juice supplementation on anaerobic and aerobic exercise performance. Journal of sports sciences, 33(14), pp.1459-1466.
  66. Bailey, S.J., Blackwell, J.R., Williams, E., Vanhatalo, A., Wylie, L.J., Winyard, P.G. and Jones, A.M., 2016. Two weeks of watermelon juice supplementation improves nitric oxide bioavailability but not endurance exercise performance in humans. Nitric Oxide, 59, pp.10-20.

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