Outcome
    Moderate Evidence

    L-Citrulline for Oxygen Utilization Improvement

    Citrulline improves blood flow and reduces perceived exertion, but its effect on true oxygen utilisation is modest.

    Overview

    Citrulline improves blood flow and reduces perceived exertion, but its effect on true oxygen utilisation is modest.

    Verdict

    Mixed evidence

    How It Works

    Citrulline raises plasma arginine more effectively than arginine itself, increasing nitric oxide synthesis, vasodilation and muscle perfusion.

    Dosing & Protocol

    Typical dose

    Recommended dose
    6-8 g citrulline malate 60 minutes pre-exercise (studied dose)
    Expected timeframe
    Assessed acutely per exercise session

    Protocol

    dose
    6-8 g citrulline malate
    form
    Citrulline malate 2:1
    timing
    Pre-exercise
    duration
    Assessed acutely

    Evidence

    What the studies say

    Meta-analyses of citrulline malate show small improvements in high-intensity endurance and reduced muscle soreness. Effects on VO2max specifically are inconsistent, and trained athletes respond less than untrained participants.

    Dietary nitrate reduces the oxygen cost of exercise: a systematic review and meta-analysis

    Score: 7/10
    2016
    meta_analysis

    Pawlak-Chaouch M, Boissiere J, Gamelin FX +3 more

    Nitrate significantly reduced the oxygen cost of submaximal exercise in non-elite participants

    View source

    Beetroot juice supplementation, plasma nitrite and exercise performance: a systematic review and meta-analysis

    Score: 7/10
    2013
    meta_analysis
    n=268

    Hoon MW, Johnson NA, Chapman PG +1 more

    Nitrate elevated plasma nitrite and improved time-to-exhaustion

    View source

    Safety

    Caveats

    MIXED verdict — some trials show improved oxygen kinetics, others do not; expectations should be modest. Nitrate/PDE5 interaction applies. Pregnancy data lacking.

    Less likely to help if

    Trained endurance athletes least likely to benefit

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