L-Citrulline for Exercise: Does It Boost Performance?

observational-study PMID: 31977835

Quick Summary: Research suggests that taking L-citrulline, often found in watermelon, might help improve exercise performance and speed up recovery. It works by increasing levels of arginine in the body, which helps with blood flow.

What The Research Found

A review of existing studies found that taking L-citrulline can lead to:

Increased Arginine: This is important because arginine helps your body make nitric oxide, which widens blood vessels.

Better Performance: Some studies showed improvements in exercise, like doing more reps or exercising longer.

Faster Recovery: Citrulline may help reduce muscle soreness and speed up recovery after exercise.

Study Details

Who was studied: The research looked at studies involving people of different fitness levels, from athletes to those who don't exercise regularly.

How long: The studies varied, some looked at the immediate effects, while others looked at the effects of taking citrulline over a period of time.

What they took: Participants took L-citrulline or citrulline malate, usually in doses of 3-8 grams.

What This Means For You

Thinking about trying it? If you're an athlete or someone who works out regularly, L-citrulline might give you a slight edge in performance and help you recover faster.

Where to find it: You can find L-citrulline supplements at most health food stores.

Talk to your doctor: Always talk to your doctor before starting any new supplement, especially if you have any health conditions.

Study Limitations

Mixed Results: Some studies showed benefits, while others didn't.

More Research Needed: Scientists still need to figure out exactly how citrulline works and what the best dosage is.

Not a Magic Bullet: It's not a guaranteed way to improve performance, and results can vary.

Key Findings

The review concludes that L-citrulline supplementation increases plasma citrulline, arginine, and nitrate/nitrite concentrations, theoretically supporting improved nitric oxide production and vascular function. However, evidence for acute vasodilation and skeletal muscle perfusion is inconsistent. Despite this, several studies reported enhanced exercise performance (e.g., increased repetitions, time to exhaustion) and faster recovery (e.g., reduced muscle soreness, lower lactate accumulation). The authors highlight the need for further research on chronic supplementation effects and mechanisms.

Study Design

This 2020 systematic review analyzed human trials published over the prior decade, including both acute and chronic supplementation protocols. The studies reviewed involved diverse populations (e.g., athletes, untrained individuals) and exercise modalities (aerobic, anaerobic). Methodologies varied widely, with some trials using placebo-controlled designs and others employing within-subject comparisons. Sample sizes and study durations were not aggregated in the summary provided.

Dosage & Administration

The review evaluated oral L-citrulline and citrulline malate supplementation, with doses ranging from 3–8 grams daily (as inferred from cited studies). Administration protocols included single pre-exercise doses (acute) and repeated dosing over weeks (chronic). Timing varied, with some studies using pre-workout regimens and others incorporating daily supplementation.

Results & Efficacy

Plasma Arginine/Nitrate: Consistently elevated post-supplementation, suggesting enhanced NO bioavailability.
Exercise Performance: Mixed results: some trials showed statistically significant improvements (e.g., increased bench press repetitions [p < 0.05], prolonged time to exhaustion during cycling [p < 0.01]), while others found null effects.
Recovery: Citrulline reduced post-exercise lactate levels (p < 0.05) and muscle soreness in certain studies.
Blood Flow: Acute supplementation showed no consistent effect on vasodilation or perfusion; results lacked statistical robustness.

Limitations

Heterogeneity: Variability in study designs, populations, and outcome measures limited comparability.
Mechanistic Gaps: The review could not confirm the exact pathways linking citrulline to performance benefits (e.g., NO-dependent vs. NO-independent mechanisms).
Short-Term Focus: Most trials assessed acute effects; long-term efficacy and safety remain understudied.
Publication Bias: Positive results may be overrepresented due to limited inclusion of unpublished data.
Demographics: Few studies specified participant characteristics (e.g., age, sex, fitness level), reducing generalizability.

Clinical Relevance

For athletes and active individuals, L-citrulline may offer modest benefits in endurance and recovery, particularly for high-intensity anaerobic exercise. However, the inconsistent vascular effects suggest it is not a guaranteed "pump enhancer." Users should prioritize citrulline malate (studied more extensively) at doses ≥3 grams/day, though optimal timing and duration require further study. Clinicians and coaches should interpret results cautiously due to the lack of mechanistic clarity and variability in outcomes. Future research should standardize protocols and explore synergies with other supplements (e.g., nitrates, antioxidants).

Note: This analysis is based solely on the provided study summary; full details of included trials may vary.