Taking L-arginine supplements every day for 8 weeks won’t make highly trained female handball players any better at running for 12 minutes straight.

Taking L-arginine supplements while doing intense interval training won’t make highly trained female handball players any faster or stronger in short sprints than training alone.

If highly trained female handball players do intense interval workouts, take L-arginine supplements, or do both, their ability to quickly change direction and move agilely gets worse after 8 weeks.

Taking arginine supplements for just three days won’t make you stronger or more powerful during short, intense workouts like sprinting or lifting heavy weights—even if you’re already a well-trained athlete.

Taking 6 grams of L-arginine might help young men use less oxygen when they exercise at a steady pace, which could mean their body works more efficiently.

Taking 6 grams of L-arginine might help young men exercise harder for longer before getting tired, by about a quarter more time than usual.