Taking a 5-gram dose of L-arginine won’t help healthy young men cycle better or lower ammonia in their blood, even though it does raise levels of a few other related chemicals in their blood.

In healthy young men, a single 5g dose of L-arginine compared to placebo would be administered in a randomized order with at least 7-day washout. Plasma ammonia, arginine, ornithine, and citrulline levels would be measured at baseline and 1, 2, and 4 hours post-ingestion. Cycling performance would be assessed via a standardized time-trial (e.g., 5km or 20km) at 2 hours post-ingestion. The analysis would compare mean changes in all outcomes between supplement and placebo conditions.

Healthy young men would be randomly assigned to receive either 5g L-arginine or placebo in a single dose. Plasma amino acid levels and cycling performance (same standardized time-trial) would be measured 2 hours after ingestion. The primary analysis would compare the mean change in ammonia and performance between groups using ANCOVA adjusting for baseline values.

Healthy young men would consume a standardized diet for 24 hours before two test days: one with 5g L-arginine and one with placebo, administered in random order. Plasma amino acids and cycling performance would be measured under identical conditions (time of day, fasting state, environmental controls). Changes in ammonia and performance would be compared within individuals across conditions.

A small group of healthy young men (n=10) would receive 5g L-arginine and have plasma amino acids measured at multiple time points. Cycling performance would be assessed at peak arginine elevation. Correlations between changes in arginine, ornithine, citrulline and ammonia or performance would be calculated to test if the biochemical changes predict functional outcomes.

Existing datasets from prior exercise studies where participants ingested 5g L-arginine and had plasma amino acids and cycling performance measured would be re-analyzed. Only studies with identical protocols (dose, timing, performance test) would be included. The analysis would test whether arginine supplementation was associated with changes in ammonia or performance across subjects.