Taking L-citrulline or L-arginine supplements doesn’t seem to help swimmers go faster in short races like 100m or 200m—maybe because these races are so quick that your body doesn’t use the kind of blood flow changes those supplements try to create.

Taking L-citrulline or L-arginine supplements doesn't seem to help competitive swimmers swim faster in 100m or 200m races, even though scientists thought these supplements might help by improving blood flow or reducing muscle burn.

Taking L-citrulline or L-arginine supplements for 8 days doesn’t help trained swimmers and triathletes feel less burned out or reduce the buildup of lactic acid in their blood during short, intense freestyle races.

Taking L-citrulline or L-arginine supplements for eight days doesn’t make swimmers any faster in 100m or 200m races, even if they’re trained athletes.

Taking L-citrulline or L-arginine pills for eight days doesn’t boost the body’s nitric oxide levels in elite swimmers and triathletes during their normal training, so these supplements don’t seem to help improve blood flow in this situation.