Taking a specific amino acid supplement called L-citrulline every day for a week, then taking one more dose an hour before a short, intense bike ride, helps trained male cyclists finish the ride 1.5% faster.

A study where healthy trained men (n≥20) complete two 4-km cycling time trials under controlled conditions: one after 7 days of 2.4g/day L-citrulline + 2.4g pre-exercise dose, and one after identical placebo regimen, with at least 7-day washout between conditions. Primary outcome is time to complete 4-km trial, with 1.5% reduction as the target effect size.

A study where healthy trained men are randomly assigned to either L-citrulline (2.4g/day for 7 days + 2.4g pre-exercise) or placebo group, then complete a single 4-km cycling time trial. Primary outcome is time to completion, with statistical comparison between groups to detect 1.5% difference.

A study where each healthy trained man completes multiple 4-km time trials under L-citrulline and control conditions (no supplement or placebo), with order randomized and blinded to participants. Time differences are analyzed to detect 1.5% improvement.

A study tracking healthy trained men who self-administer L-citrulline (2.4g/day for 7 days + 2.4g pre-exercise) and measure their 4-km cycling time before and after the intervention to detect a 1.5% reduction.

A report describing 3–5 trained male cyclists who took L-citrulline as described and noted faster 4-km times, without controls or statistical analysis.