Taking a daily L-arginine supplement for two weeks doesn't make healthy young men cycle any harder or faster in a short, self-paced test compared to taking a sugar pill.

A study where 20-30 healthy young men each complete two 15-minute self-paced cycling tests: one after 14 days of 5 g/day L-arginine and one after 14 days of placebo, with a washout period between. Mean power output is measured and compared within each participant.

A study where 40-60 healthy young men are randomly assigned to either 5 g/day L-arginine or placebo for 14 days, then all perform a single 15-minute self-paced cycling test. Mean power output is compared between groups.

A study where each participant completes multiple 15-minute self-paced cycling tests under tightly controlled conditions (same time of day, diet, sleep, warm-up) after 14 days of L-arginine and 14 days of placebo, with order randomized and blinded.

A study tracking healthy young men who self-select to take 5 g/day L-arginine for 14 days versus those who do not, then measuring mean power output during a 15-minute self-paced cycling test.

A small group of healthy young men take 5 g/day L-arginine for 14 days and perform a 15-minute self-paced cycling test before and after, with no placebo control.