The Truth About L-Citrulline Summary
- The study found that acute L-Citrulline supplementation (8 g) did not significantly improve resistance exercise performance, muscle oxygenation, or subjective measures of perceived effort, energy, focus, fatigue, and muscle pump compared to a placebo in recreationally resistance-trained men and women.
- Specifically, no differences were observed between the citrulline and placebo groups for peak force during the isometric mid-thigh pull test, ballistic bench press power and velocity, or the total repetitions and volume completed during the strength-endurance bench press.
- It is important to note that this study only examined the acute effects of L-Citrulline supplementation and did not investigate its potential long-term effects or benefits. However, this study adds to the growing literature that L-Citrulline may not be effective for increasing muscle pumps or performance.
Introduction to L-Citrulline Biochemistry
In the world of fitness and bodybuilding, many athletes and enthusiasts have sought ways to enhance their exercise performance and achieve better muscle pumps. One supplement that has garnered significant attention in recent years is L-citrulline. L-citrulline is a non-essential amino acid primarily found in watermelons, cucumbers, and other melons.
L-Citrulline Supplements Benefits Compared to L-Arginine
Touted as a potential ergogenic aid, L-citrulline is believed to increase nitric oxide (NO) production and improve blood flow, leading to enhanced athletic performance and muscle pump during workouts. Nitric oxide is a molecule that helps to relax and widen blood vessels, improving blood flow and oxygen delivery to muscles. However, recent scientific studies have challenged these claims, suggesting that acute L-citrulline supplementation may not deliver the promised benefits. In this research-based essay, we will delve into the existing scientific literature to evaluate the effects of L-citrulline on exercise performance and muscle pumps, aiming to debunk the myth surrounding its efficacy.
What is L-Citrulline: Theoretical Rationale Behind L-Citrulline Supplementation
Exploring the theoretical rationale behind its supplementation is crucial to understanding the hype surrounding L-citrulline. L-citrulline is a non-essential amino acid primarily found in watermelon. Upon ingestion, it is converted into L-arginine, which serves as a precursor to nitric oxide. Increased nitric oxide levels enhance vasodilation, promoting greater blood flow and oxygen delivery to working muscles during exercise.
Nitric oxide can improve exercise performance and reduce fatigue. It plays an important role in the urea cycle, which helps to remove ammonia from the body. This theory has led to incorporating L-citrulline into pre-workout supplements, claiming improved exercise performance and muscle pumps. (Gonzalez & Trexler, 2020)
Unlike direct L-arginine supplementation, which undergoes significant catabolism in the gut and first-pass metabolism, L-citrulline may have better systemic availability for promoting NO synthesis. (Gonzalez et al., 2023) This suggests that increased nitric oxide levels during resistance exercise could enhance vasodilation and blood flow, potentially delaying fatigue and improving strength and power expression. Consequently, L-citrulline has become a prominent ingredient in commercially available pre-workout supplements designed to enhance exercise performance.(Aguayo et al., 2021; Gonzalez & Trexler, 2020)
Citrulline Malate vs. L-Citrulline: Unraveling the Difference:
There two distinct forms of the amino acid citrulline (i.e., Citrulline Malate and L-Citrulline). Citrulline Malate is a combination of citrulline and malic acid commonly found in sports supplements, while L-Citrulline is the pure form of citrulline that is often used for its potential benefits on exercise performance.
Another area of interest is comparing L-citrulline and citrulline malate, a combination of L-citrulline and malic acid often used in pre-workout supplements. Citrulline malate, a combination of L-citrulline and malic acid, is another popular ingredient in pre-workout supplements. It is believed to provide additional benefits, including enhanced ammonia detoxification and improved recovery from exhaustive exercise.
Studies on citrulline malate’s effects on resistance exercise performance have yielded mixed results. While some studies reported benefits such as delayed fatigue, improved power output, and increased work performed during resistance exercise, others failed to show significant ergogenic effects. Clarifying the differences between L-citrulline and citrulline malate can aid individuals in making informed decisions when selecting supplements. (Chappell et al., 2018; Farney et al., 2019; Fick et al., 2021; Gills et al., 2023)
However, it is essential to understand that dietary supplementation with L-citrulline alone may not significantly improve exercise performance. Clarifying the differences between the two forms can help individuals make informed decisions when selecting supplements. (Sureda & Pons, 2012)
L-Citrulline Dosage and Formulation:
Citrulline malate is commonly administered in an acute 8 g dose with a 1:1 or 2:1 ratio, resulting in approximately 4.0 to 5.3 g of L-citrulline and 3.7 to 4.0 g of malate. Some studies have reported that this 8 g dose of citrulline malate can lead to delayed fatigue, improved power output, and increased work capacity during resistance exercise. However, contrasting findings have been observed in other studies, where no significant ergogenic benefit was evident following the same 8 g dosage of citrulline malate.
A meta-analysis conducted by Vårvik et al. and Trexler et al. revealed slight enhancements in repetitions to failure (approximately 6.4% or ~3 repetitions) and strength-power performance, respectively, in the context of high-intensity strength training and L-citrulline supplementation. Despite the small effect sizes reported in these meta-analyses, further research, especially focusing on higher doses, is warranted to understand citrulline malate’s potential benefits comprehensively. (E. T. Trexler et al., 2019)
Scientific Evidence on L-Citrulline and Exercise Performance: Does L-Citrulline Work?
A. Meta-analysis of Citrulline Supplementation and Endurance Performance:
In the quest to validate the claims of improved exercise performance with L-citrulline, several meta-analyses have been conducted. These studies have assessed the effects of acute citrulline supplementation on endurance measures such as time-to-exhaustion (TTE) and time-trial completion (TTC). Surprisingly, the results of these analyses indicate that acute citrulline supplementation does not significantly enhance endurance performance compared to a control group in young, healthy adults. The evidence challenges the widely held belief that L-citrulline boosts aerobic exercise performance.(Harnden et al., 2023)
B. L-Citrulline and High-Intensity Strength and Power Performance:
Several studies have investigated the effects of citrulline malate on resistance exercise performance, typically provided in an 8 g dose with a 1:1 or 2:1 ratio of L-citrulline to malate. While some studies have reported improvements in the number of repetitions performed during sets of multi-joint exercises, others have failed to demonstrate significant benefits. Meta-analyses have indicated small effect sizes in relation to high-intensity strength training and L-citrulline supplementation. Still, the inconclusive results call for further research, particularly with higher doses. (Glenn et al., 2016; Glenn et al., 2017; Trexler, Persky, et al., 2019)
Here are a few studies that have found no benefit to taking Citrulline malate and exercise performance:
- Gonzalez and colleagues investigated the impact of citrulline malate supplementation on resistance exercise performance. The participants performed a protocol consisting of five sets of bench press at 75% of one-repetition maximum (1RM) with 2-minute rest intervals. The researchers administered 8 g of citrulline malate as an acute dose but found no improvement in the number of repetitions completed during the bench press sets.(Gonzalez et al., 2018)
- Trexler and colleagues investigated the effects of citrulline malate supplementation on performance during an isokinetic dynamometer protocol consisting of five sets of 30 maximal-effort single-leg extensions. Participants were given 8 g of citrulline malate as an acute dose. However, as the other studies mentioned earlier, Trexler et al. failed to observe any performance-enhancing benefits following the administration of citrulline malate in this particular resistance exercise protocol. (Trexler, Keith, et al., 2019)
Debunking the Myth: L-Citrulline’s Impact on Muscle Pumps:
One of the primary claims associated with L-citrulline supplementation is its ability to increase muscle pumps during resistance training. Muscle pumps, also known as the “pump” or muscle engorgement, are characterized by increased blood flow and fluid accumulation in the muscles during intense exercise.
The claim that L-citrulline enhances muscle pumps during resistance training is widely debated in the scientific literature. Some studies suggest that L-citrulline may indirectly improve muscle pumps by promoting vasodilation and increased blood flow. However, direct evidence supporting this claim is limited, necessitating additional research to validate its efficacy. (Cutrufello et al., 2015; Gonzalez et al., 2022; Gough et al., 2021)
New Study Casts Doubt on Citrulline as a Pump Ingredient
Given the disparity of research studies finding positive and negative results with l-citrulline and resistance exercise performance, researchers examined the effect of supplementing with 8 g of L-citrulline on resistance exercise performance and muscle oxygenation in recreationally resistance-trained men and women.
The study evaluated the effects of L-Citrulline supplementation on muscular performance during the isometric mid-thigh pull (IMTP), ballistic bench press protocols, and a strength-endurance bench press protocol. Additionally, subjective assessments of perceived effort, energy, focus, fatigue, and muscle pump were analyzed. In a randomized, double-blind, crossover design, the participants completed two experimental trials, separated by at least 48 h. In one trial, they received a placebo (PL); in the other, they received L-Citrulline (CIT) at a dose of 8 g/day.
The study results showed no significant differences in any of the results between the placebo and 8 grams of citrulline before exercise. The performance between the conditions (L-citrulline supplementation and placebo) for the IMTP (isometric mid-thigh pull) and ballistic bench press protocols. The total repetitions completed and volume load were similar between the conditions.
There were also no significant differences in muscle oxygenation between the conditions. The subjective assessments of perceived effort, energy, focus, fatigue, and muscle pump did not show any significant differences between the conditions, except for higher fatigue and muscle pump reported by women compared to men. The study found no significant effects of acute L-citrulline supplementation on resistance exercise performance.(Gonzalez 2023)
One important limitation of the study was that the study administered a single acute dose of L-citrulline, and it’s possible that chronic dosing of L-citrulline may be more effective for enhancing exercise performance.
L-Citrulline, a supplement commonly promoted for enhancing exercise performance, has garnered mixed results in scientific studies. While some studies suggest that L-Citrulline may improve certain aspects of exercise performance, others show no significant benefits. Individual responses to L-Citrulline can also vary, indicating the need for further research to fully understand its effects.
While L-citrulline has shown promise in certain contexts, such as potentially enhancing high-intensity exercise performance and nitric oxide bioavailability, it may not universally translate to improved endurance or muscle pumps. As the fitness community seeks evidence-based practices, this research-based essay aims to guide readers in making informed decisions regarding L-citrulline supplementation. Athletes and fitness enthusiasts can optimize their training routines and achieve performance goals by embracing a balanced and scientific approach.
Aguayo, E., Martínez-Sánchez, A., Fernández-Lobato, B., & Alacid, F. (2021). L-Citrulline: A Non-Essential Amino Acid with Important Roles in Human Health. Applied Sciences, 11(7), 3293. https://www.mdpi.com/2076-3417/11/7/3293
Chappell, A. J., Allwood, D. M., Johns, R., Brown, S., Sultana, K., Anand, A., & Simper, T. (2018). Citrulline malate supplementation does not improve German Volume Training performance or reduce muscle soreness in moderately trained males and females. Journal of the International Society of Sports Nutrition, 15(1), 42. https://doi.org/10.1186/s12970-018-0245-8
Cutrufello, P. T., Gadomski, S. J., & 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), 1459-1466. https://doi.org/10.1080/02640414.2014.990495
Farney, T. M., Bliss, M. V., Hearon, C. M., & Salazar, D. A. (2019). The Effect of Citrulline Malate Supplementation on Muscle Fatigue Among Healthy Participants. The Journal of Strength & Conditioning Research, 33(9), 2464-2470. https://doi.org/10.1519/jsc.0000000000002356
Fick, A. N., Kowalsky, R. J., Stone, M. S., Hearon, C. M., & Farney, T. M. (2021). Acute and Chronic Citrulline Malate Supplementation on Muscle Contractile Properties and Fatigue Rate of the Quadriceps. Int J Sport Nutr Exerc Metab, 31(6), 490-496. https://doi.org/10.1123/ijsnem.2021-0117
Gills, J. L., Spliker, B., Glenn, J. M., Szymanski, D., Romer, B., Lu, H.-C., & Gray, M. (2023). Acute Citrulline-Malate Supplementation Increases Total Work in Short Lower-Body Isokinetic Tasks for Recreationally Active Females During Menstruation. The Journal of Strength & Conditioning Research, 37(6), 1225-1230. https://doi.org/10.1519/jsc.0000000000004095
Glenn, J. M., Gray, M., Jensen, A., Stone, M. S., & Vincenzo, J. L. (2016). Acute citrulline-malate supplementation improves maximal strength and anaerobic power in female, masters athletes tennis players. Eur J Sport Sci, 16(8), 1095-1103. https://doi.org/10.1080/17461391.2016.1158321
Glenn, J. M., Gray, M., Wethington, L. N., Stone, M. S., Stewart, R. W., & Moyen, N. E. (2017). Acute citrulline malate supplementation improves upper- and lower-body submaximal weightlifting exercise performance in resistance-trained females. European Journal of Nutrition, 56(2), 775-784. https://doi.org/10.1007/s00394-015-1124-6
Gonzalez, A. M., Pinzone, A. G., Lipes, S. E., Mangine, G. T., Townsend, J. R., Allerton, T. D., Sell, K. M., & Ghigiarelli, J. J. (2022). Effect of watermelon supplementation on exercise performance, muscle oxygenation, and vessel diameter in resistance-trained men. European Journal of Applied Physiology, 122(7), 1627-1638. https://doi.org/10.1007/s00421-022-04940-4
Gonzalez, A. M., Spitz, R. W., Ghigiarelli, J. J., Sell, K. M., & Mangine, G. T. (2018). Acute Effect of Citrulline Malate Supplementation on Upper-Body Resistance Exercise Performance in Recreationally Resistance-Trained Men. The Journal of Strength & Conditioning Research, 32(11), 3088-3094. https://doi.org/10.1519/jsc.0000000000002373
Gonzalez, A. M., Townsend, J. R., Pinzone, A. G., & Hoffman, J. R. (2023). Supplementation with Nitric Oxide Precursors for Strength Performance: A Review of the Current Literature. Nutrients, 15(3). https://doi.org/10.3390/nu15030660
Gonzalez, A. M., & Trexler, E. T. (2020). Effects of Citrulline Supplementation on Exercise Performance in Humans: A Review of the Current Literature. J Strength Cond Res, 34(5), 1480-1495. https://doi.org/10.1519/jsc.0000000000003426
Gonzalez, A.M.; Yang, Y.; Mangine, G.T.; Pinzone, A.G.; Ghigiarelli, J.J.; Sell, K.M. Acute Effect of L-Citrulline Supplementation on Resistance Exercise Performance and Muscle Oxygenation in Recreationally Resistance Trained Men and Women. J. Funct. Morphol. Kinesiol. 2023, 8, 88. https://doi.org/10.3390/jfmk8030088
Gough, L. A., Sparks, S. A., McNaughton, L. R., Higgins, M. F., Newbury, J. W., Trexler, E., Faghy, M. A., & Bridge, C. A. (2021). A critical review of citrulline malate supplementation and exercise performance. Eur J Appl Physiol, 121(12), 3283-3295. https://doi.org/10.1007/s00421-021-04774-6
Harnden, C. S., Agu, J., & Gascoyne, T. O. M. (2023). Effects of citrulline on endurance performance in young healthy adults: a systematic review and meta-analysis. Journal of the International Society of Sports Nutrition, 20(1), 2209056. https://doi.org/10.1080/15502783.2023.2209056
Sureda, A., & Pons, A. (2012). Arginine and citrulline supplementation in sports and exercise: ergogenic nutrients? Med Sport Sci, 59, 18-28. https://doi.org/10.1159/000341937
Trexler, E. T., Keith, D. S., Schwartz, T. A., Ryan, E. D., Stoner, L., Persky, A. M., & Smith-Ryan, A. E. (2019). Effects of Citrulline Malate and Beetroot Juice Supplementation on Blood Flow, Energy Metabolism, and Performance During Maximum Effort Leg Extension Exercise. The Journal of Strength & Conditioning Research, 33(9), 2321-2329. https://doi.org/10.1519/jsc.0000000000003286
Trexler, E. T., Persky, A. M., Ryan, E. D., Schwartz, T. A., Stoner, L., & Smith-Ryan, A. E. (2019). Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis. Sports Medicine, 49(5), 707-718. https://doi.org/10.1007/s40279-019-01091-z
Frequently Asked Questions
Unveiling the Potency of Citrulline: An Extensive Appraisal
Citrulline, a non-essential amino acid found in watermelons, cucumbers, and other melons, has garnered significant attention in the USA and in the scientific community due to its potential health benefits. From its role in enhancing blood circulation and cardiovascular health to its impact on muscle strength and erectile dysfunction, citrulline has become a subject of fascination in the realm of dietary supplements. In this article, we delve into the biochemistry of citrulline and its potential effects on various health aspects, including blood pressure, hypertension, erectile dysfunction, and more.
The Symbiosis between Citrulline and Nitric Oxide Production
One of the key factors contributing to citrulline’s reputation is its involvement in nitric oxide synthesis. Nitric oxide is a crucial molecule known for its ability to relax and dilate blood vessels, leading to improved blood flow and circulation. Citrulline plays a significant role in the production of nitric oxide through the enzymatic action of nitric oxide synthase (NOS). This mechanism suggests a potential link between citrulline supplementation and blood pressure regulation, plasma phosphate levels, and the function of arteries. Citrulline’s involvement in the urea cycle has also piqued interest in its potential to support kidney function. The ability to efficiently eliminate ammonia may have implications for individuals with kidney issues, helping to reduce the burden on this vital organ.
Blood Pressure and Hypertension: Citrulline’s Prospective Perks
Hypertension, commonly known as high blood pressure, is a prevalent cardiovascular condition affecting millions of individuals in the United States and worldwide. . Studies have explored the effects of citrulline on blood pressure in healthy subjects and those with hypertension. Research indicates that citrulline may promote vasodilation, thus helping to lower blood pressure levels and reduce the risk of cardiovascular disease. Additionally, recent studies have highlighted citrulline’s potential to alleviate inflammation and endothelial dysfunction in the arteries.
Citrulline and Endothelial Functionality
The endothelium, a thin layer of cells lining blood vessels, plays a crucial role in maintaining vascular health. Endothelial dysfunction, characterized by impaired endothelial function, is a significant factor contributing to cardiovascular diseases. Recent studies suggest that citrulline could positively impact endothelial cells, promoting their health and functionality. By supporting endothelial cells, citrulline may contribute to overall cardiovascular health and potentially benefit individuals with conditions like pulmonary hypertension and heart failure. Moreover, citrulline might have a role in maintaining calcium homeostasis, contributing to cardiovascular health.
Citrulline and Muscular Potency
Beyond its cardiovascular benefits, citrulline’s impact extends to muscle health and strength. Research has shown that citrulline supplements may aid in enhancing protein synthesis and reducing muscle fatigue. These effects are particularly relevant for older adults seeking to maintain muscle mass and strength as they age. Additionally, athletes and fitness enthusiasts may find value in citrulline supplementation to support muscle recovery and performance during exercise. The interplay between citrulline, ornithine, and arginine in the urea cycle may also play a role in nitrogen metabolism and muscle function.
Citrulline and Erectile Dysfunction (ED)
Erectile dysfunction, a condition characterized by the inability to achieve or maintain an erection, can significantly impact a person’s quality of life. Some studies suggest that citrulline supplementation may have potential benefits for individuals with ED. Citrulline’s role in promoting nitric oxide production and improved blood flow may enhance penile circulation, thereby aiding in erectile function. Furthermore, the combination of citrulline and sildenafil, the active ingredient in Viagra, has been the subject of scientific interest in addressing ED.
Safety and Adverse Effects of Citrulline Supplements
While citrulline supplements have shown promising results in various health aspects, it is crucial to address potential side effects and safety considerations. Citrulline is generally well-tolerated in recommended dosages, but excessive intake may lead to gastrointestinal discomfort, including bloating and diarrhea. As with any dietary supplement, it is advisable to consult with a healthcare professional before incorporating citrulline into your regimen, especially if you have any underlying health conditions or are taking medications, including insulin for diabetes management and monitoring glucose levels in the blood.
Citrulline, with its multifaceted roles in nitric oxide production, cardiovascular health, muscle strength, and potential implications in erectile function, continues to captivate the attention of researchers and health enthusiasts alike. As we traverse the realm of citrulline’s biochemical intricacies, it holds the promise of unlocking new avenues for supporting overall health and well-being. From potential applications in obesity management and kidney health to its role in DNA synthesis, citrulline continues to garner scientific interest and is likely to be the focus of further studies in the years to come., it is essential to recognize that further research is imperative to fully comprehend its mechanisms of action and the extent of its efficacy in addressing specific health conditions. As with any dietary supplement, a judicious approach, in tandem with professional guidance, remains pivotal in harnessing the true potential of citrulline on our journey toward optimal health and vitality.