Taking 10 grams of L-citrulline daily for four weeks leads to a small increase in oxygen levels and a decrease in deoxygenated hemoglobin in the forearm muscles of hypertensive postmenopausal women during handgrip exercise, suggesting changes in how oxygen is delivered and used in that tissue.

Taking 10 grams of L-citrulline daily for four weeks increases blood flow and vessel dilation in the forearms of hypertensive postmenopausal women during handgrip exercise.

Taking citrulline supplements may help improve blood flow and allow more repetitions during high-repetition, short-rest workouts, but it does not cause measurable increases in muscle size over time.

Taking a specific dose of L-citrulline for 10 days doesn’t make you bike harder, faster, or feel less tired—even though some people think it might help. Your heart, lungs, and muscles act the same as if you didn’t take it.

Taking 10 grams of L-citrulline daily for four weeks lowers aortic systolic blood pressure by 4 mmHg in postmenopausal women with hypertension, without altering aortic stiffness, suggesting a direct effect on blood vessel tone.

Taking a specific amino acid called L-citrulline every day for a week, plus a little more before a bike race, helps men who are already fit ride harder for 4 kilometers without getting more out of breath — meaning their bodies use energy more efficiently.