The effect ofl-citrulline and watermelon juice supplementation on anaerobic and aerobic exercise performance

The effects of L-Citrulline and Glutathione on Endurance performance in young adult trained males

BACKGROUND

Citrulline may amplify the effects of L-arginine and nitric oxide concentration, which may augment vasodilation and blood flow, thereby enhancing aerobic exercise performance. The purpose of this randomized, double-blind, placebo-controlled crossover study was to investigate effects of L-citrulline + Glutathione on aerobic exercise performance and blood flow in well-trained men.

METHODS

Twenty-five males (Mean ± SD; Age: 22.2 ± 2.4 yrs; Height: 177.0 ± 4.8 cm; Weight: 75.3 ± 6.9 kg) were randomly assigned to the L-citrulline + Glutathione (Setria Performance Blend: SPB; L-citrulline [2 g] + glutathione [200 mg], 6 capsules) or placebo (PL; 3.1 g cellulose, 6 capsules) group. Participants performed a maximal oxygen consumption treadmill test to determine peak velocity (PV) and returned after eight days of ingesting either PL or SPB. Three timed treadmill runs to exhaustion (TTE) were performed at 90%, 100%, and 110% PV. Brachial artery blood flow and vessel diameter were assessed using ultrasound at 1-hr prior to exercise (1hrPrEX), after each exercise bout, immediately post-exercise (immediate PEX), and 30 minutes post exercise (30minPEX) at visits 2 and 4. Blood analytes were assessed via venous blood draws at visit 1, visit 3, and 1hrPEX, immediate PEX, and 30minPEX at visits 2 and 4. After a 14-day washout, participants repeated the same procedures, ingesting the opposite treatment. Separate repeated measures ANOVAs were performed for TTE, vessel diameter, blood flow, and blood analytes.

RESULTS

Blood flow was significantly augmented 30minPEX (p = 0.04) with SPB in comparison with PL. L-citrulline and L-arginine plasma concentrations were significantly elevated immediately PEX (p = 0.001) and 30-minPEX (p = 0.001) following SPB in comparison to PL.

CONCLUSION

Acute ingestion of SPB after eight days may enhance blood flow, L-citrulline, and L-arginine plasma concentrations after high-intensity exercise, which may enhance performance.

CLINICAL TRIAL REGISTRATION

[https://clinicaltrials.gov/ct2/show/nct04090138], identifier [NCT04090138].

Effects of citrulline on endurance performance in young healthy adults: a systematic review and meta-analysis

BACKGROUND

Citrulline is a popular dietary supplement, primarily thought to exert ergogenic effects on exercise performance through the enhancement of nitric oxide (NO) synthesis and ammonia buffering. However, recent findings surrounding citrulline's effect on endurance performance have been inconsistent. A systematic review and meta-analysis of the relevant literature have yet to be undertaken.

AIM

To determine if acute ingestion of citrulline has an ergogenic effect on endurance performance in young healthy adults.

METHODS

A systematic search of three databases was undertaken to find peer-reviewed randomized controlled trials (RCTs) published in English investigating the effects of citrulline supplementation on endurance performance in young healthy adults. Two independent investigators completed a three-phased screening procedure against pre-determined eligibility criteria. Included studies evaluated loading or bolus dosage regimes of citrulline in participants aged 18 or over that were at least recreationally active. Outcome measures focused on time-to-completion (TTC) or time-to-exhaustion (TTE) in continuous submaximal intensity exercise. Cochrane's Risk of Bias 2 (RoB 2) tool was used to assess the risk of bias in individual studies. Meta-analysis was conducted using a fixed-effects model to pool the weighted estimate of standardized mean differences (SMD) across studies. A chi-squared test assessed heterogeneity between studies. This review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Nine studies (n = 158 participants) met the eligibility criteria; five reported TTE outcomes (I² = 0%, χ² = 0.37, df = 4, P = 0.99) and four reported TTC outcomes (I² = 0%, χ² = 0.46, df = 3, P = 0.93), both with a low between-study heterogeneity. The results of the meta-analyses showed no significant difference in the endurance performance measures, TTE (pooled SMD = 0.03 [-0.27, 0.33]) and TTC (pooled SMD = -0.07 [-0.50, 0.15]), after acute ingestion of citrulline supplementation or a control in young healthy adults.

DISCUSSION

The current evidence suggests no significant benefit of citrulline supplementation for endurance performance. However, the small evidence base requires further research to fully evaluate this topic. Recommendations include a focus on female populations; higher continuous doses of citrulline over seven days; and TTC outcome measures over longer distances to simulate competition.

Watermelon consumption decreases risk factors of cardiovascular diseases: A systematic review and meta-analysis of randomized controlled trials

This meta-analysis was conducted to examine the effects of watermelon supplementation on cardiovascular diseases (CVDs) risk factors in randomized controlled trials (RCTs). The comprehensive search was done in Cochrane Library databases, ISI Web of Science, PubMed, and Scopus up to March 2022. A random-effect model was used for computing weighted mean differences (WMD). Standard methods were applied to examine publication bias, sensitivity analysis, and heterogeneity. Of the 8962 identified studies, 9 RCTs were included in the final analysis. Watermelon consumption significantly decreased systolic blood pressure (SBP), total cholesterol (TC) and low-density lipoprotein (LDL). In addition, watermelon consumption led to a significant increase in fasting blood sugar (FBS). However, there was not any significant difference in other outcomes of interest including diastolic blood pressure (DBP), heart rate (HR), BMI, body fat, and serum levels of arginine, insulin, and CRP after watermelon supplementation. The current findings provide promising evidence of the antihypertensive effect of watermelon. However, due to the lack of evidence in human research, the result regarding the remaining outcomes needs to be used with caution. Furter RCTs with longer follow-ups and larger sample sizes should be done to confirm the current findings.

Acute Effect of L-Citrulline Supplementation on Resistance Exercise Performance and Muscle Oxygenation in Recreationally Resistance Trained Men and Women

L-citrulline serves as a nitric oxide precursor with the potential to increase blood flow and improve resistance exercise performance, yet more research is needed to examine its ergogenic potential. To examine the effect of L-citrulline supplementation on resistance exercise performance, muscle oxygenation, and the subjective perception of effort, energy, focus, fatigue, and muscle pump, eighteen resistance-trained men (n = 11) and women (n = 7) (21.4 ± 1.8 years; 172.3 ± 7.5 cm; 76.9 ± 10.8 kg) were randomly assigned for supplementation with 8 g of L-citrulline (CIT) or a placebo (PL) in a cross-over fashion one hour prior to testing. Participants completed an isometric mid-thigh pull test (IMTP), a ballistic bench press protocol [two sets of two repetitions at 75% 1-repetition maximum (1 RM) with maximum ballistic intent], and a strength-endurance bench press protocol [five repetition-maximum sets at 75% 1RM]. Barbell velocity and power were measured via a linear position transducer during the ballistic protocol, while the repetitions completed, volume load and muscle oxygenation were quantified during the strength-endurance protocol. Subjective measures were assessed at the baseline and immediately pre- and post-exercise. Repeated measures of the analysis of variance and Bayesian equivalents revealed no significant interactions, providing evidence favoring the null hypothesis (BF10 < 1) for IMTP (PL 497.5 ± 133.6 vs. CIT 492.5 ± 129.4 N), barbell velocity, and power, and repetitions completed (PL 36.7 ± 7.2 vs. CIT 36.9 ± 8.1 repetitions). There were also no significant interactions for muscle oxygenation parameters or subjective measures except perceived fatigue. Women reported greater fatigue across all time points compared to men (~1.88 au, p = 0.045, BF10 = 0.2). The results indicate that a single 8 g dose of L-citrulline did not enhance isometric force production, muscle endurance, or muscle oxygenation parameters during the protocol implemented in this study.

Dietary Arginine and Citrulline Supplements for Cardiovascular Health and Athletic Performance: A Narrative Review

The global market for nutritional supplements (NS) is growing rapidly, and the use of L-arginine (Arg), L-citrulline (Cit), and citrulline malate (CitMal) supplements has been shown to enhance cardiovascular health and athletic performance. Over the past decade, Arg, Cit, and CitMal supplements have received considerable attention from researchers in the field of exercise nutrition, who have investigated their potential effects on hemodynamic function, endothelial function, aerobic and anaerobic capacity, strength, power, and endurance. Previous studies were reviewed to determine the potential impact of Arg, Cit, and CitMal supplements on cardiovascular health and exercise performance. By synthesizing the existing literature, the study aimed to provide insight into the possible uses and limitations of these supplements for these purposes. The results showed that both recreational and trained athletes did not see improved physical performance or increased nitric oxide (NO) synthesis with 0.075 g or 6 g doses of Arg supplement per body weight. However, 2.4 to 6 g of Cit per day for 7 to 16 days of various NSs had a positive impact, increasing NO synthesis, enhancing athletic performance indicators, and reducing feelings of exertion. The effects of an 8 g acute dose of CitMal supplement were inconsistent, and more research is needed to determine its impact on muscle endurance performance. Based on the positive effects reported in previous studies, further testing is warranted in various populations that may benefit from nutritional supplements, including aerobic and anaerobic athletes, resistance-trained individuals, elderly people, and clinical populations, to determine the impact of different doses, timing of ingestion, and long-term and acute effects of Arg, Cit, and CitMal supplements on cardiovascular health and athletic performance.

Supplementation with Nitric Oxide Precursors for Strength Performance: A Review of the Current Literature

Nitric-oxide-stimulating dietary supplements are widely available and marketed to strength athletes and weightlifters seeking to increase muscle performance and augment training adaptations. These supplements contain ingredients classified as nitric oxide (NO) precursors (i.e., "NO boosters"). Endogenous NO is generated via a nitric oxide synthase (NOS)-dependent pathway and a NOS-independent pathway that rely on precursors including L-arginine and nitrates, with L-citrulline serving as an effective precursor of L-arginine. Nitric oxide plays a critical role in endothelial function, promoting relaxation of vascular smooth muscle and subsequent dilation which may favorably impact blood flow and augment mechanisms contributing to skeletal muscle performance, hypertrophy, and strength adaptations. The aim of this review is to describe the NO production pathways and summarize the current literature on the effects of supplementation with NO precursors for strength and power performance. The information will allow for an informed decision when considering the use of L-arginine, L-citrulline, and nitrates to improve muscular function by increasing NO bioavailability.

The effects of fresh foods on performance: A review

In recent years, it is gradually becoming important for athletes to show sufficient performance at competitions. To improve performance, athletes use ergogenic aids such as protein powders, creatine, and glutamine. However, recent research has also been conducted into the possible ergogenic effects of several fresh foods on exercise. Nutrients show the ergogenic effect by having macro and micronutrients, antioxidants, vitamins, minerals, and bioactive components. These potential ergogenic effects include muscle recovery, prevention of oxidative stress caused by exercise, improved performance, and inhibition of muscle damage. The purpose of this review was to examine the nutritional content and the effects of fresh foods such as beets, cherries, watermelon, tomatoes, grapes, and pomegranate.

Effects of Citrulline Supplementation on Different Aerobic Exercise Performance Outcomes: A Systematic Review and Meta-Analysis

Supplementation with Citrulline (Cit) has been shown to have a positive impact on aerobic exercise performance and related outcomes such as lactate, oxygen uptake (VO₂) kinetics, and the rate of perceived exertion (RPE), probably due to its relationship to endogenous nitric oxide production. However, current research has shown this to be controversial. The main objective of this systematic review and meta-analysis was to analyze and assess the effects of Cit supplementation on aerobic exercise performance and related outcomes, as well as to show the most suitable doses and timing of ingestion. A structured literature search was carried out by the PRISMA^® (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and PICOS guidelines in the following databases: Pubmed/Medline, Scopus, and Web of Science (WOS). A total of 10 studies were included in the analysis, all of which exclusively compared the effects of Cit supplementation with those of a placebo group on aerobic performance, lactate, VO₂, and the RPE. Those articles that used other supplements and measured other outcomes were excluded. The meta-analysis was carried out using Hedges’ g random effects model and pooled standardized mean differences (SMD). The results showed no positive effects of Cit supplementation on aerobic performance (pooled SMD = 0.15; 95% CI (−0.02 to 0.32); I², 0%; p = 0.08), the RPE (pooled SMD = −0.03; 95% CI (−0.43 to 0.38); I², 49%; p = 0.9), VO₂ kinetics (pooled SMD = 0.01; 95% CI (−0.16 to 0.17); I², 0%; p = 0.94), and lactate (pooled SMD = 0.25; 95% CI (−0.10 to 0.59); I², 0%; p = 0.16). In conclusion, Cit supplementation did not prove to have any benefits for aerobic exercise performance and related outcomes. Where chronic protocols seemed to show a positive tendency, more studies in the field are needed to better understand the effects.

The Effects of Consuming Amino Acids L-Arginine, L-Citrulline (and Their Combination) as a Beverage or Powder, on Athletic and Physical Performance: A Systematic Review

Consumption of amino acids L-arginine (L-Arg) and L-citrulline (L-Cit) are purported to increase nitric oxide (NO) production and improve physical performance. Clinical trials have shown relatively more favorable outcomes than not after supplementing with L-Cit and combined L-Arg and L-Cit. However, in most studies, other active ingredients such as malate were included in the supplement. Therefore, the aim of this study was to determine the efficacy of consuming standalone L-Arg, L-Cit, and their combination (in the form of powder or beverage) on blood NO level and physical performance markers. A systematic review was undertaken following PRISMA 2020 guidelines (PROSPERO: CRD42021287530). Four electronic databases (PubMed, Ebscohost, Science Direct, and Google scholar) were used. An acute dose of 0.075 g/kg of L-Arg or 6 g L-Arg had no significant increase in NO biomarkers and physical performance markers (p > 0.05). Consumption of 2.4 to 6 g/day of L-Cit over 7 to 16 days significantly increased NO level and physical performance markers (p < 0.05). Combined L-Arg and L-Cit supplementation significantly increased circulating NO, improved performance, and reduced feelings of exertion (p < 0.05). Standalone L-Cit and combined L-Arg with L-Cit consumed over several days effectively increases circulating NO and improves physical performance and feelings of exertion in recreationally active and well-trained athletes.

Current Evidence of Watermelon (Citrullus lanatus) Ingestion on Vascular Health: A Food Science and Technology Perspective

The amino acid L-arginine is crucial for nitric oxide (NO) synthesis, an important molecule regulating vascular tone. Considering that vascular dysfunction precedes cardiovascular disease, supplementation with precursors of NO synthesis (e.g., L-arginine) is warranted. However, supplementation of L-citrulline is recommended instead of L-arginine since most L-arginine is catabolized during its course to the endothelium. Given that L-citrulline, found mainly in watermelon, can be converted to L-arginine, watermelon supplementation seems to be effective in increasing plasma L-arginine and improving vascular function. Nonetheless, there are divergent findings when investigating the effect of watermelon supplementation on vascular function, which may be explained by the L-citrulline dose in watermelon products. In some instances, offering a sufficient amount of L-citrulline can be impaired by the greater volume (>700 mL) of watermelon needed to reach a proper dose of L-citrulline. Thus, food technology can be applied to reduce the watermelon volume and make supplementation more convenient. Therefore, this narrative review aims to discuss the current evidence showing the effects of watermelon ingestion on vascular health parameters, exploring the critical relevance of food technology for acceptable L-citrulline content in these products. Watermelon-derived L-citrulline appears as a supplementation that can improve vascular function, including arterial stiffness and blood pressure. Applying food technologies to concentrate bioactive compounds in a reduced volume is warranted so that its ingestion can be more convenient, improving the adherence of those who want to ingest watermelon products daily.

The Effects of a Pre-workout Supplement on Measures of Alertness, Mood, and Lower-Extremity Power

Objective

The purpose of this study was to investigate the effects of a multi-ingredient pre-workout supplement (MIPS) on mental and physical performance.

Materials and methods

Fourteen exercise-trained men (n=7) and women (n=7) completed this randomized, placebo-controlled, double-blind, counterbalanced, crossover trial. Participants consumed either a MIPS or a placebo in a randomized, counterbalanced order. Forty-five minutes after consumption, the following assessments were conducted: psychomotor vigilance test (PVT), Profile of Mood States (POMS), vertical jump test, and heart rate and blood pressure. There was a one-week washout period between assessments.

Results

Statistically significant differences were observed between the treatment and placebo groups for the PVT (reaction time: treatment: 286 ± 28 ms, placebo: 306 ± 46 ms, p=0.0371) and POMS (i.e., vigor: treatment: 15.2 ± 14.9, placebo: 9.7 ± 9.6, p=0.0403; fatigue: treatment: 1.0 ± 1.1, placebo: 3.3 ± 3.4, p=0.0100). There were no significant differences between groups for the other indices of mood, false starts from the PVT, and vertical jump.

Conclusion

Based on our findings, the acute consumption of a MIPS produced a significant improvement in a sustained-attention, reaction-timed task as well as measures of vigor and fatigue.

Eight Days of L-Citrulline or L-Arginine Supplementation Did Not Improve 200-m and 100-m Swimming Time Trials

The effects of L-citrulline or L-arginine supplementation on exercise performance are equivocal, and the effects on swimming performance are unclear. We aimed to assess whether 8-day supplementation with L-arginine or L-citrulline supplementation would improve 200 m and 100 m freestyle swimming time-trial performances. After the baseline trial (first visit), in a double-blind, randomised design, 15 trained/developmental (5 females) swimmers and triathletes were assigned to three groups and underwent an 8-day supplementation period, with a daily dose of either 8 gr L-arginine (Arg, n = 5) or L-citrulline (Cit, n = 5) or placebo (Pla, n = 5). On day 9, participants completed experimental trial (second visit). In each trial, after blood sampling, participants performed both 200 m and 100 m freestyle swimming time-trials, with 30 min recovery between trials. Plasma nitric oxide (NOx) and blood lactate concentrations (BLa) were collected immediately before and after 200 m and 100 m TTs, respectively. No significant difference was observed in NOx between groups (p = 0.201). There was no significant difference in 200 m (p = 0.226) and 100 m swimming time-trials (p = 0.993) between groups. There was a main effect of time on BLa concentration (p < 0.001), but no trial × group (p = 0.243) and trial × lactate × group interaction effect (p = 0.276) was present. Furthermore, 8-day either L-citrulline or L-arginine supplementation did not enhance middle (200 m) and short-distance (100 m) swimming performance in trained/developmental swimmers and triathletes. These findings do not support the use of L-citrulline or L-arginine supplementation as ergogenic aids for swimming performance.

Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Increasing nitric oxide bioavailability may induce physiological effects that enhance endurance exercise performance. This review sought to evaluate the performance effects of consuming foods containing compounds that may promote nitric oxide bioavailability.

METHODS

Scopus, Web of Science, Ovid Medline, EMBASE and SportDiscus were searched, with included studies assessing endurance performance following consumption of foods containing nitrate, L-arginine, L-citrulline or polyphenols. Random effects meta-analysis was conducted, with subgroup analyses performed based on food sources, sex, fitness, performance test type and supplementation protocol (e.g. duration).

RESULTS

One hundred and eighteen studies were included in the meta-analysis, which encompassed 59 polyphenol studies, 56 nitrate studies and three L-citrulline studies. No effect on exercise performance following consumption of foods rich in L-citrulline was identified (SMD=-0.03, p=0.24). Trivial but significant benefits were demonstrated for consumption of nitrate and polyphenol-rich foods (SMD=0.15 and 0.17, respectively, p<0.001), including performance in time-trial, time-to-exhaustion and intermittent-type tests, and following both acute and multiple-day supplementation, but no effect of nitrate or polyphenol consumption was found in females. Among nitrate-rich foods, beneficial effects were seen for beetroot, but not red spinach or Swiss chard and rhubarb. For polyphenol-rich foods, benefits were found for grape, (nitrate-depleted) beetroot, French maritime pine, Montmorency cherry and pomegranate, while no significant effects were evident for New Zealand blackcurrant, cocoa, ginseng, green tea or raisins. Considerable heterogeneity between polyphenol studies may reflect food-specific effects or differences in study designs and subject characteristics. Well-trained males (V̇O2max ≥65 ml.kg.min-1) exhibited small, significant benefits following polyphenol, but not nitrate consumption.

CONCLUSION

Foods rich in polyphenols and nitrate provide trivial benefits for endurance exercise performance, although these effects may be food dependent. Highly trained endurance athletes do not appear to benefit from consuming nitrate-rich foods but may benefit from polyphenol consumption. Further research into food sources, dosage and supplementation duration to optimise the ergogenic response to polyphenol consumption is warranted. Further studies should evaluate whether differential sex-based responses to nitrate and polyphenol consumption are attributable to physiological differences or sample size limitations.

OTHER

The review protocol was registered on the Open Science Framework ( https://osf.io/u7nsj ) and no funding was provided.

Effects of L-citrulline supplementation and watermelon consumption on longer-term and postprandial vascular function and cardiometabolic risk markers: A meta-analysis of randomized controlled trials in adults

L-citrulline may improve non-invasive vascular function and cardiometabolic risk markers through increases in L-arginine bioavailability and nitric oxide synthesis. A meta-analysis of randomized controlled trials (RCTs) was performed to examine longer-term and postprandial effects of L-citrulline supplementation and watermelon consumption on these markers for cardiovascular disease in adults. Summary estimates of weighted mean differences (WMDs) in vascular function and cardiometabolic risk markers with accompanying 95% confidence intervals (CIs) were calculated using random or fixed-effect meta-analyses. Seventeen RCTs were included involving an L-citrulline intervention, of which six studied postprandial and twelve longer-term effects. Five studies investigated longer-term effects of watermelon consumption and five assessed effects during the postprandial phase. Longer-term L-citrulline supplementation improved brachial artery flow-mediated vasodilation (FMD) by 0.9 %-point (95 % CI: 0.7 to 1.1, P < 0.001). Longer-term watermelon consumption improved pulse wave velocity by 0.9 m/s (95% CI: 0.1 to 1.5, P < 0.001), while effects on FMD were not studied. No postprandial effects on vascular function markers were found. Postprandial glucose concentrations decreased by 0.6 mmol/L (95% CI: 0.4 to 0.7, P < 0.001) following watermelon consumption, but no other longer-term or postprandial effects were observed on cardiometabolic risk markers. To conclude, longer-term L-citrulline supplementation and watermelon consumption may improve vascular function, suggesting a potential mechanism by which increased L-citrulline intake beneficially affects cardiovascular health outcomes in adults. No effects on postprandial vascular function markers were found, while more research is needed to investigate effects of L-citrulline and watermelon on risk markers related to cardiometabolic health.

L-Citrulline Supplementation and Exercise in the Management of Sarcopenia

Sarcopenia is a process associated to aging. Persistent inflammation and oxidative stress in muscle favour muscle wasting and decreased ability to perform physical activity. Controlled exercise can optimize blood flux and moderate the production of reactive oxygen species. Therefore, supplements that can work as a vasodilators and control oxidative stress, might be beneficial for active elders. In this context, we have tested citrulline supplementation in a group of 44 participants aged from 60–73 years that followed a physical activity program adapted to their age and capacities. Volunteers were divided in two groups: placebo (n = 22) and citrullline supplemented (n = 22). Different physical tests and blood extractions were performed at the beginning and at the end of intervention (six weeks). Strength and endurance showed a tendency to increase in the citrulline supplemented group, with no significant differences respect to placebo. However, walking speed in the citrulline supplemented group improved significantly compared to placebo. Markers of muscle damage as well as circulating levels of testosterone, cortisol and vitamin D showed no significant changes, but a tendency to improve at the end of intervention in the supplemented group compared to placebo. Additional studies are necessary to confirm the effect of citrulline supplementation in sarcopenia delay.

Citrulline, Biomarker of Enterocyte Functional Mass and Dietary Supplement. Metabolism, Transport, and Current Evidence for Clinical Use

L-Citrulline is a non-essential but still important amino acid that is released from enterocytes. Because plasma levels are reduced in case of impaired intestinal function, it has become a biomarker to monitor intestinal integrity. Moreover, oxidative stress induces protein citrullination, and antibodies against anti-citrullinated proteins are useful to monitor rheumatoid diseases. Citrullinated histones, however, may even predict a worse outcome in cancer patients. Supplementation of citrulline is better tolerated compared to arginine and might be useful to slightly improve muscle strength or protein balance. The following article shall provide an overview of L-citrulline properties and functions, as well as the current evidence for its use as a biomarker or as a therapeutic supplement.

The Effects of L-Citrulline on Blood-Lactate Removal Kinetics Following Maximal-Effort Exercise

The accumulation of lactate in muscle and blood during high-intensity exercise is negatively correlated with the duration exercise can be sustained. Removal of lactate is a key component of acute recovery between consecutive bouts of such exercise. Low-intensity exercise enhances recovery by accelerating lactate turnover in metabolically active tissues, largely mediated by blood flow to these tissues. Therefore, the purpose of this research was to clarify if L-citrulline, a nutritional supplement purported to promote vasodilation via enhanced nitric oxide availability, would augment the removal of blood lactate during active recovery (AR). L-citrulline ingestion will augment the rate of blood lactate concentration decrease during AR, reduce the oxygen-cost of submaximal exercise, and increase time-to-exhaustion and peak oxygen uptake (V̇O2peak) during a test of maximal aerobic power. Healthy university students (five males & five females) participated in this double-blind, randomized, placebo-controlled study. Participants exercised on a cycle ergometer at submaximal steady-state intensities followed by progressively increasing intensity to exhaustion, 10 min of AR, and then supramaximal intensity exercise to exhaustion. Oxygen uptake was measured throughout the trial and blood lactate was sampled repeatedly during AR. The protocol elicited very high peak blood lactate concentrations after exercise (11.3 + 1.3 mmol/L). L-citrulline supplementation did not significantly alter blood lactate kinetics during AR, the oxygen cost of exercise, V̇O2peak, or time-to-exhaustion. Despite a strong theoretical basis by which L-citrulline could augment lactate removal from the blood, L-citrulline supplementation showed no effect as an exercise-recovery supplement.

Acute Effect of Citrulline Malate on Repetition Performance During Strength Training: A Systematic Review and Meta-Analysis

Citrulline malate (CitMal) is a dietary supplement that is suggested to enhance strength training performance. However, there is conflicting evidence on this matter. Thus, the purpose of this meta-analysis was to determine whether supplementing with CitMal prior to strength training could increase the total number of repetitions performed before reaching voluntary muscular failure. A systematic search was conducted wherein the inclusion criteria were double-blind, placebo-controlled studies in healthy participants that examined the effect of CitMal on repetitions to failure during upper body and lower body resistance exercises. The Hedges's g standardized mean differences (SMD) between the placebo and CitMal trials were calculated and used in a random effect model. Two separate subanalyses were performed for upper body and lower body exercises. Eight studies, including 137 participants who consisted of strength-trained men (n = 101) and women (n = 26) in addition to untrained men (n = 9), fulfilled the inclusion criteria. Across the studies, 14 single-joint and multijoint exercises were performed with an average of 51 ± 23 total repetitions during 5 ± 3 sets per exercise at ∼70% of one-repetition maximum. Supplementing with 6-8 g of CitMal 40-60 min before exercise increased repetitions by 3 ± 5 (6.4 ± 7.9%) compared with placebo (p = .022) with a small SMD (0.196). The subanalysis for the lower body resulted in a tendency for an effect of the supplement (8.1 ± 8.4%, SMD: 0.27, p = .051) with no significant effect for the upper body (5.7 ± 8.4%, SMD: 0.16, p = .131). The current analysis observed a small ergogenic effect of CitMal compared with placebo. Acute CitMal supplementation may, therefore, delay fatigue and enhance muscle endurance during high-intensity strength training.

L-Citrulline: A Non-Essential Amino Acid with Important Roles in Human Health

L-Arginine (Arg) has been widely used due to its functional properties as a substrate for nitric oxide (NO) generation. However, L-citrulline (CIT), whose main natural source is watermelon, is a non-essential amino acid but which has important health potential. This review provides a comprehensive approach to different studies of the endogenous synthesis of CIT, metabolism, pharmacokinetics, and pharmacodynamics as well as its ergogenic effect in exercise performance. The novel aspect of this paper focuses on the different effects of CIT, citrulline malate and CIT from natural sources such as watermelon on several topics, including cardiovascular diseases, diabetes, erectile dysfunction, cancer, and exercise performance. CIT from watermelon could be a natural food-sourced substitute for pharmacological products and therefore the consumption of this fruit is promoted.

[The effect of supplementation with L-arginine and L-citrulline on physical performance: a systematic review]

Introduction

Introduction: the amino acids L-arginine (L-arg) and L-citrulline (L-citr) have been used in sports nutrition, and it is believed that they have an effect on physical performance. However, current information is varied and inconclusive. Objective: to review and analyze the scientific evidence in the last ten years, which reflects a connection between the effect of L-arg and L-citr supplementation and physical performance. Material and method: this study is a systematic review of articles previously published, following the PRISMA model. Those articles published between 2008 and 2018 that connected the effect of L-arg and L-citr supplementation with physical performance were analyzed. The electronic search was performed on Web of Science, Scopus, Sport Discus, PubMed, and Medline. All articles using a supplementation protocol with these amino acids, separately or in groups, were selected. Results: a total of 38 articles were found, which were stratified according to the established protocol: a) supplementation with L-arg (n = 19); b) supplementation with L-arg and L-citr (n = 1); and c) supplementation with L-citr (n = 18), whether of short or prolonged duration. Conclusion: there is evidence that L-citr works better as ergogenic than L-arg does on physical performance, since L-citr showed a positive effect on the rate of perceived exertion and muscular pain, in addition to a decrease in lactate concentrations and time in maximum tests. However, there is not enough evidence to establish a beneficial L-citr dosage for physical performance.

L-Citrulline Supports Vascular and Muscular Benefits of Exercise Training in Older Adults

Age-associated reduction in endothelial nitric oxide (NO) synthesis contributes to the development of cardiovascular diseases and sarcopenia. L-Citrulline is a precursor of NO with the ability to improve vascular function and muscle protein synthesis. We hypothesize that vascular and muscular benefits associated with oral L-citrulline supplementation might be augmented by concomitant supplementation with exercise training in older adults.

Therapeutic Potential of Citrulline as an Arginine Supplement: A Clinical Pharmacology Review

Supplemental arginine has shown promise as a safe therapeutic option to improve endogenous nitric oxide (NO) regulation in cardiovascular diseases associated with endothelial dysfunction. In clinical studies in adults, L-arginine, an endogenous amino acid, was reported to improve cardiovascular function in hypertension, pulmonary hypertension, preeclampsia, angina, and MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome. L-citrulline, a natural precursor of L-arginine, is more bioavailable than L-arginine because it avoids hepatic first-pass metabolism and has a longer circulation time. Although not yet well-studied, arginine/citrulline has immense therapeutic potential in some life-threatening diseases in children. However, the optimal clinical development of arginine or citrulline in children requires more information about pharmacokinetics and exposure-response relationships at appropriate ages and under relevant disease states. This article summarizes the preclinical and clinical studies of arginine/citrulline in both adults and children, including currently available pharmacokinetic information. The pharmacology of arginine/citrulline is confounded by several patient-specific factors such as variations in baseline arginine/citrulline due to developmental ages and disease states. Currently available pharmacokinetic studies are insufficient to inform the optimal design of clinical studies, especially in children. Successful bench-to-bedside clinical translation of arginine supplementation awaits information from well-designed pharmacokinetic/pharmacodynamic studies, along with pharmacometric approaches.

Acute effects of Nitrosigine® and citrulline malate on vasodilation in young adults

Background

Athletes are increasingly exploring ways to enhance their physical performance. Increasing blood flow to the working tissues through endothelium-dependent vasodilation is one factor athletes use to realize these results. Sports supplements such as pre-workouts tout this benefit; however, many have not been tested under laboratory conditions to examine the effects of commonly used supplements on vasodilation. Two popular supplements are Nitrosigine® and citrulline malate (CM). Thus, the purpose of this experiment was to determine the effects of Nitrosigine and CM on vasodilation using ultrasound and flow mediated dilation (FMD).

Methods

Healthy, normotensive, and physically active male (n = 16) and female (n = 8) young adults participated in the present investigation. We utilized a randomized, double-blind, within-subjects design where participants reported for three trials, each preceded by a 7-day washout period. Baseline FMD measurement was obtained for each visit, followed by consumption of one clinical dose CM (8 g), Nitrosigine (1.5 g), or dextrose placebo (8 g). Following a 60-min digestion period, FMD was repeated. Supplementation order was randomized controlling for potential order effects.

Results

Repeated measures ANOVA yielded a significant supplement (3) x time (2) effect (p < .001), such that Nitrosigine and CM yielded a greater improvement in FMD response than placebo. After supplementation, Nitrosigine and CM increased FMD by 31 and 34%, respectively, compared to a decrease of 2% during the placebo trial. After allometric scaling of the FMD values, supplement x time effect remained significant (p = .001) and changes were similar to non-scaled results. Nitrosigine (23%) and CM (25%) generated significantly greater allometric scaled FMD values when compared to the placebo trial (0.60%).

Discussion

Both Nitrisigine and CM increased endothelial-dependent vasodilation as measured by a change in FMD. Increased vasodilation leads to an increase in skeletal muscle blood flow resulting in potential improvements in exercise performance.

The Physiological Effects of Amino Acids Arginine and Citrulline: Is There a Basis for Development of a Beverage to Promote Endurance Performance? A Narrative Review of Orally Administered Supplements

Nutritional and ergogenic aid supplementation is prevalent within athletic or general fitness populations, and is only continuing to gain momentum. Taken in isolation or as a combination, amino acid (AA) supplementation has the potential to increase endurance performance among other benefits. L-Arginine (L-Arg) and L-Citrulline (L-Cit) are two AAs proposed to increase endothelial nitric oxide (NO) synthesis, with potential additional physiological benefits, and therefore may contribute to enhanced performance outcomes such as increased power output, or time to exhaustion. However, the appropriate dose for promoting physiological and performance benefits of these AAs, and their potential synergistic effects remains to be determined. Therefore, the aim of this review was to evaluate the varied concentrations used in the current literature, assess the effects of L-Arg and L-Cit in combination on physiological responses and endurance performance, and consider if there is a fundamental basis for providing these supplements in the form of a beverage. A total of six studies were considered eligible for the review which utilized a range of 3–8 g of the AA constituents. The findings support the notion that supplementing with a combination of L-Arg and L-Cit may increase NO production, enhance vasodilation, and therefore increase performance capacity in athletes. A beverage as a carrier for the two AAs is worth considering; however, there remains limited research assessing these outcomes across a consistent range of concentrations in order to see their full potential.

Fruits

Fruits come in a wide variety of colors, shapes, and flavors. This chapter will cover selected fruits that are known to be healthy and highly nutritious. These fruits were chosen due to their common usage and availability. Since it is not possible to cover all health benefits or essential nutrients and important phytochemicals of the fruit composition, this chapter will focus on the key valuable constituents and their potential health effects.

Acute citrulline-malate supplementation is ineffective during aerobic cycling and subsequent anaerobic performance in recreationally active males

Citrulline-malate (CM) purportedly increases exercise performance through increased nitric oxide production. The effects of CM on muscular strength performance are well-documented; however, the benefits of CM on aerobic and anaerobic biking performance are not well researched. Therefore, the present investigation examined the acute CM supplementation effects on aerobic and anaerobic cycling performance in recreationally active males. Methods: 28 recreationally active males (20.9 ± 2.8 years) completed randomized, double-blind, crossover trials consuming CM (12g dextrose + 8g CM) or a placebo (12g dextrose). Participants performed an aerobic cycling protocol (time-to-exhaustion [TTE]), followed by a subsequent 30-second Wingate cycling test, 60-minutes after supplement consumption. Results: Dependent t-tests showed no significant differences (p > 0.05) for TTE (PLA: 315.4 s ± 137.7 s; CM: 314.1 s ± 107.1 s) and Total Work Completed (TWC) (PLA: 74.7 ± 34.1 kilojoules (kJ); CM: 74.1 ± 26.4 kJ) during the aerobic cycling protocol. Dependent t-tests also showed no significant differences (p > 0.05) for mean watts (PLA: 586.1 ± 87.7 Watts (W); CM: 588.0 ± 93.0 W), peak watts (PLA: 773.0 ± 136.7 W; CM: 786.7 ± 133.0 W), and fatigue index (PLA: 12.9 ± 6.4 FI; CM: 14.3 ± 7.2 FI) during the Wingate protocol. Repeated-measures ANOVA results indicated a significant effect between each 5 s interval (p < 0.001), but no differences were observed between trials (p > 0.05). Conclusion: Acute CM supplementation in recreationally active males provides no ergogenic benefit in aerobic cycling performance followed by an anaerobic cycling test.

l-Citrulline supplementation improves glucose and exercise tolerance in obese male mice

NEW FINDINGS

What is the central question of the study? Does the action of l-citrulline, which has been shown to augment performance in animals and athletes, possibly via increasing mitochondrial function, translate to obese animals, and does this improve glycaemia? What is the main finding and its importance? Chronic supplementation with l-citrulline improves not only exercise capacity, but also glycaemia in obese mice, which would be beneficial as obese individuals are at increased risk for type 2 diabetes. However, l-citrulline supplementation also caused a mild impairment in insulin signalling and insulin tolerance in obese mice. ABSTRACT: l-Citrulline is an organic α-amino acid that has been shown to have a number of salutary actions on whole-body physiology, including reducing muscle wasting and augmenting exercise and muscle performance. The latter has been suggested to arise from elevations in mitochondrial function. Because enhancing mitochondrial function has been proposed as a novel strategy to mitigate insulin resistance, our goal was to determine whether supplementation with l-citrulline could also improve glycaemia in an experimental mouse model of obesity. We hypothesized that l-citrulline treatment would improve glycaemia in obese mice, and this would be associated with elevations in skeletal muscle mitochondrial function. Ten-week-old C57BL/6J mice were fed either a low-fat (10% kcal from lard) or a high-fat (60% kcal from lard) diet, while receiving drinking water supplemented with either vehicle or l-citrulline (0.6 g l^-1 ) for 15 weeks. Glucose homeostasis was assessed via glucose/insulin tolerance testing, while in vivo metabolism was assessed via indirect calorimetry, and forced exercise treadmill testing was utilized to assess endurance. As expected, obese mice supplemented with l-citrulline exhibited an increase in exercise capacity, which was associated with an improvement in glucose tolerance. Consistent with augmented mitochondrial function, we observed an increase in whole body oxygen consumption rates in obese mice supplemented with l-citrulline. Surprisingly, l-citrulline supplementation worsened insulin tolerance and reduced insulin signalling in obese mice. Taken together, although l-citrulline supplementation improves both glucose tolerance and exercise capacity in obese mice, caution must be applied with its broad use as a nutraceutical due to a potential deterioration of insulin sensitivity.

Citrulline and Arginine Content of Taxa of Cucurbitaceae

Watermelon is the most significant, natural plant source of L-citrulline, a non-proteinaceous amino acid that benefits cardiovascular health and increases vasodilation in many tissues of the body. Watermelon is a member of the Cucurbitaceae, which includes squash, melon, pumpkin, and cucumber. It is possible that other cucurbits could be good sources of citrulline or of arginine, its direct precursor. Twenty-one cultigens were evaluated in triplicate at two locations in North Carolina to estimate citrulline and arginine amounts and variation due to cultigen, replication, and environment. Cultigens containing the highest amount of citrulline (based on LS means) in g/kg fresh weight were ’Crimson Sweet’ watermelon (2.85), ’Dixielee’ watermelon (2.43), casaba-type melon (0.86), mouse melon (0.64), and horned melon rind (0.45). Additionally, mouse melon, horned melon, and bitter gourd (arils) may be interesting sources of arginine-family amino acids, perhaps because of their large seed and aril content relative to mesocarp.

Supplementation of 100% Flesh Watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] Juice Improves Swimming Performance in Rats

Nutritional intervention of fruit juice supplementation is able to maximize exercise performance. Watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] contains high L-citrulline content and consumption of watermelon juice may promote ergogenic effects. The aim of the present study was to investigate the role of 100% flesh watermelon juice and 100% rind watermelon juice supplementation for 14 days on swimming performance in rats. Twenty four male Sprague-Dawley rats were randomly divided into four groups: Cx group of rats supplemented with filtered tap water (negative control), L-cit group of rats supplemented with L-citrulline (positive control), FR group of rats supplemented with 100% flesh watermelon juice, and RR group of rats supplemented with 100% rind watermelon juice. Each group was supplemented for 14 days ad libitum prior to swimming exercise protocol. The rats were performed swimming exercise for 3 days and swimming time until exhaustion was measured. Plasma samples were collected to measure lactate concentration, ammonia concentration, and nitric oxide production. Rats supplemented with 100% flesh watermelon juice demonstrated significantly prolonged of swimming time until exhaustion, reduction of lactate and ammonia concentrations, and increased of nitric oxide production compared to Cx and L-cit groups (P<0.05). These findings postulate that supplementation with 100% flesh watermelon juice improves endurance in swimming performance.

A combination of oral L-citrulline and L-arginine improved 10-min full-power cycling test performance in male collegiate soccer players: a randomized crossover trial

PURPOSE

Oral L-citrulline (Cit) increases plasma L-arginine (Arg) concentration and the production of nitric oxide (NO). NO dilates blood vessels and potentially improves sports performance. The combination of oral Arg and Cit (Arg + Cit) immediately and synergistically increases plasma Arg and nitrite/nitrate (NOx) concentrations more than either Cit or Arg alone. This prompted us to assess the effects of oral Arg + Cit on 10-min cycling performance in a double-blind, randomized, placebo-controlled crossover trial.

METHODS

Twenty-four male soccer players ingested either Cit + Arg or placebo (both 1.2 g/day each) for 6 days. On day 7, they ingested Cit + Arg 1 h before performing a 10-min full-power pedaling test on a bicycle ergometer. Plasma NOx and amino acid levels were measured before and after the test, as well as the participants' subjective perception of physical exertion.

RESULTS

Power output was significantly greater with Cit + Arg than in the placebo group (242 ± 24 vs. 231 ± 21 W; p < 0.05). Plasma concentrations of post-exercise NOx (p < 0.05), Cit (p < 0.01) and Arg (p < 0.01) were significantly higher in the Cit + Arg than in the placebo group, whereas exercise upregulated plasma NOx concentrations in both groups (p < 0.05). Cit + Arg also gave improved post-exercise subjective perception of "leg muscle soreness" and "ease of pedaling" (both p < 0.05).

CONCLUSION

Seven days of oral Citrulline (1.2 g/d) and Arginine (1.2 g/d) ingestion improved 10-min cycling performance and the perception of physical exertion in male collegiate soccer players.

Supplements with purported effects on muscle mass and strength

PURPOSE

Several supplements are purported to promote muscle hypertrophy and strength gains in healthy subjects, or to prevent muscle wasting in atrophying situations (e.g., ageing or disuse periods). However, their effectiveness remains unclear.

METHODS

This review summarizes the available evidence on the beneficial impacts of several popular supplements on muscle mass or strength.

RESULTS

Among the supplements tested, nitrate and caffeine returned sufficient evidence supporting their acute beneficial effects on muscle strength, whereas the long-term consumption of creatine, protein and polyunsaturated fatty acids seems to consistently increase or preserve muscle mass and strength (evidence level A). On the other hand, mixed or unclear evidence was found for several popular supplements including branched-chain amino acids, adenosine triphosphate, citrulline, β-Hydroxy-β-methylbutyrate, minerals, most vitamins, phosphatidic acid or arginine (evidence level B), weak or scarce evidence was found for conjugated linoleic acid, glutamine, resveratrol, tribulus terrestris or ursolic acid (evidence level C), and no evidence was found for other supplements such as ornithine or α-ketoglutarate (evidence D). Of note, although most supplements appear to be safe when consumed at typical doses, some adverse events have been reported for some of them (e.g., caffeine, vitamins, α-ketoglutarate, tribulus terrestris, arginine) after large intakes, and there is insufficient evidence to determine the safety of many frequently used supplements (e.g., ornithine, conjugated linoleic acid, ursolic acid).

CONCLUSION

 In summary, despite their popularity, there is little evidence supporting the use of most supplements, and some of them have been even proven ineffective or potentially associated with adverse effects.

Obesitas: Pentingkah Memperhatikan Konsumsi Makanan di Akhir Pekan?

Background: The prevalence of obesity in all age groups has increased in some countries. Epidemiological studies indicated that the intake of energy and macronutrient over the weekend were increasing rather than on weekdays and contributed to the incidence of obesity. Objectives: The aim of this literature review is to analyze the different between intake of energy and macronutrients in weekdays compared to weekend and how it contributes to obesity . Methode: The literature review method used international journal article that was searched using the electronic database such as Medline NCBI (National Center for Biotechnology Information), embases, and google scholar.Result: The results showed that energy and macronutrient intake were increasing over the weekend than on weekdays. Consumption of unhealthy food on weekend such as foods and beverages with high sugar, high fat and alcohol increase the energy and play a role in the incidence of obesity. Conclusion: The health promotion concerning food intake on weekdays and weekend both in terms of quantity and quality is needed for obesity prevention.ABSTRAKLatar belakang: Prevalensi obesitas pada semua kelompok umur meningkat di hampir seluruh negara di dunia. Studi epidemiologi menunjukkan bahwa asupan energi dan zat gizi makro diakhir pekan meningkat dibandingkan hari biasa dan berperan pada kejadian obesitas.Tujuan: Tujuan dari literatur review ini adalah untuk menganalisis perbedaan asupan energi dan zat gizi makro diakhir pekan dibandingkan hari biasa dan bagaimana kontribusinya terhadap obesitas.Metode: Metode yang digunakan adalah metode penelusuran artikel  jurnal internasional yang ditelusuri menggunakan electronic database seperti medline NCBI (National Center for Biotechnology Information), embase, dan penelusuran dengan google schoolar.Hasil: Hasil telaah beberapa artikel menunjukan bahwa rata-rata asupan energi dan zat gizi makro mengalami peningkatan saat akhir pekan dibandingkan hari biasa. Konsumsi unhealthy food di akhir pekan seperti makanan dan minuman dengan kandungan tinggi gula, tinggi lemak, dan alkohol tampaknya menyebabkan peningkatan kalori dan berperan pada insiden obesitas.Kesimpulan: Diperlukan upaya pencegahan obesitas melalui promosi kesehatan masyarakat dengan memperhatikan asupan makanan saat hari libur baik dari segi kuantitas maupun kualitasnya.

Peran Asam Amino Sitrulin dalam Meningkatkan Performa Olahraga Pada Atlet

Background: Citrulline is an ergogenic non-essential amino acid which is able to increase production, efficiency, and use of energy, as well as performance in sport. Purpose: The objective of this literature review was to explain the role of citrulline in improving exercise performance through both aerobic and anaerobic metabolic pathways. Discussion: The results showed evidence that citrulline has role in improving exercise performance. Several articles indicate that the consumption of citrulline either supplement or watermelon given during certain period or acute before the test might increase VO2max, retard muscle fatigue, and decrease delayed onset muscle soreness. Some studies used 6-8 g citrulline before exercise, but lower dose was used in some other studies. Conclusion: Amino acids citrulline either supplement or watermelon is believed to have role in improving exercise performance in athletes although there is no recommendation dose has been found. ABSTRAKLatar Belakang: Sitrulin merupakan asam amino non esensial yang bersifat ergogenik yaitu dapat meningkatkan produksi, efisiensi, dan penggunaan energi serta performa olahraga.Tujuan: Tujuan penulisan kajian pustaka ini adalah untuk menjabarkan peran sitrulin dalam meningkatkan performa olahraga melalui jalur metabolisme baik aerobik maupun anaerobik.Ulasan: Hasil literature review menunjukkan bukti bahwa sitrulin memiliki peran dalam meningkatkan performa olahraga atlet. Beberapa artikel menunjukkan bahwa konsumsi sitrulin baik dalam bentuk suplemen maupun buah semangka yang diberikan selama jangka waktu tertentu maupun sesaat sebelum dilakukan tes latihan fisik mampu meningkatkan VO2max, menunda kelelahan otot, dan mengurangi rasa nyeri otot pasca latihan. Beberapa penelitian menggunakan dosis 6-8 g sitrulin sebelum olahraga, beberapa penelitian lain menggunakan dosis yang lebih rendah.Kesimpulan: Asam amino sitrulin baik dalam bentuk suplemen maupun buah semangka diyakini memiliki peran dalam meningkatkan performa olahraga atlet walaupun rekomendasi dosis baku yang disarankan belum ditemukan.

Citrulline malate supplementation does not improve German Volume Training performance or reduce muscle soreness in moderately trained males and females

BACKGROUND

Use of supplements to aid performance is common practice amongst recreationally active individuals, including those without a sufficient evidence base. This investigation sought to assess whether acute supplementation with 8 g of citrulline malate (CM) (1.11: 1 ratio) would improve anaerobic performance.

METHODS

A randomised double blind placebo control trial was employed, using a counterbalanced design. We recruited recreationally active men and women to take part in an isokinetic chair protocol, based on German Volume Training (GVT) whereby participants attempted to perform 10 sets of 10 repetitions against a force representing 70% of their peak concentric force.

RESULTS

The number of repetitions achieved over the course of the GVT was 94.0 ± 7.9 and 90.9 ± 13.9 for placebo and CM respectively. There was no significant difference between the placebo and CM treatment for number of repetitions (P = 0.33), isometric (P = 0.60), concentric (P = 0.38), or eccentric (P = 0.65) peak force following the GVT. Total muscle soreness was significantly higher in the CM compared to the placebo treatment following the GVT protocol over 72 h (P = 0.01); although this was not accompanied by a greater workload/number of repetitions in the CM group.

CONCLUSIONS

We conclude that an acute dose of CM does not significantly affect anaerobic performance using an isokinetic chair in recreational active participants. Practical implications include precaution in recommending CM supplementation. Coaches and athletes should be aware of the disparity between the chemical analyses of the products reviewed in the present investigation versus the manufacturers' claims.

ISSN exercise & sports nutrition review update: research & recommendations

Background

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult.

Methods

This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches.

Conclusions

This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

l-Citrulline Supplementation-Increased Skeletal Muscle PGC-1α Expression Is Associated with Exercise Performance and Increased Skeletal Muscle Weight

SCOPE

l-citrulline has recently been reported as a more effective supplement for promoting intracellular nitric oxide (NO) production compared to l-arginine. Here, the effect of l-citrulline on skeletal muscle and its influence on exercise performance were investigated. The underlying mechanism of its effect, specifically on the expression of skeletal muscle peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), was also elucidated.

METHODS AND RESULTS

Six-week-old ICR mice were orally supplemented with l-citrulline (250 mg kg-1 ) daily, and their performance in weight-loaded swimming exercise every other day for 15 days, was evaluated. In addition, mice muscles were weighed and evaluated for the expression of PGC-1α and PGC-1α-regulated genes. Mice orally supplemented with l-citrulline had significantly higher gastrocnemius and biceps femoris muscle mass. Although not statistically significant, l-citrulline prolonged the swimming time to exhaustion. PGC-1α upregulation was associated with vascular endothelial growth factor α (VEGFα) and insulin-like growth factor 1 (IGF-1) upregulation. VEGFα and IGF-1 are important for angiogenesis and muscle growth, respectively, and are regulated by PGC-1α. Treatment with NG-nitro-l-arginine methyl ester hydrochloride (l-NAME), a nitric oxide synthesis inhibitor, suppressed the l-citrulline-induced PGC-1α upregulation in vitro.

CONCLUSION

Supplementation with l-citrulline upregulates skeletal muscle PGC-1α levels resulting in higher skeletal muscle weight that improves time to exhaustion during exercise.

Citrulline Malate Does Not Improve Muscle Recovery after Resistance Exercise in Untrained Young Adult Men

The effects of citrulline malate (CM) on muscle recovery from resistance exercise remains unknown. We aimed to determine if citrulline malate supplementation improves muscle recovery after a single session of high-intensity resistance exercise (RE) in untrained young adult men. Nine young adult men (24.0 ± 3.3 years) participated in a double-blind crossover study in which they received 6 g of CM and placebo (PL) on two occasions, separated by a seven-day washout period. Each occasion consisted of a single session of high-intensity RE (0 h) and three subsequent fatigue tests sessions (at 24, 48, and 72 h) to assess the time course of muscle recovery. During the tests sessions, we assessed the following variables: number of maximum repetitions, electromyographic signal (i.e., root mean square (RMS) and median frequency (MF)), muscle soreness and perceived exertion, as well as blood levels of creatine kinase (CK), lactate, insulin, and testosterone:cortisol ratio. CK levels increased at 24 h post-exercise and remained elevate at 48 and 72 h, with no difference between CM and PL conditions. Muscle soreness increased at 24 h post-exercise, which progressively returned to baseline at 72 h in both conditions. Lactate levels increased immediately post-exercise and remained elevated at 24, 48, and 72 h in both conditions. No significant treatment × time interaction was found for all dependents variables (maximum repetitions, perceived exertion, CK, lactate, RMS, MF, and testosterone:cortisol ratio) during the recovery period. In conclusion, our data indicate that CM supplementation (single 6 g dose pre-workout) does not improve the muscle recovery process following a high-intensity RE session in untrained young adult men.