Taking a specific supplement called L-citrulline before and during a tough bike workout may cause your body to use up more of certain amino acids (BCAAs) for energy, which means less of them are left floating in your blood.

A study where healthy trained men receive L-citrulline (2.4g/day for 7 days + 2.4g pre-exercise) and a placebo in randomized order, with plasma BCAA levels measured during standardized high-intensity cycling bouts. Primary outcome: change in plasma BCAA concentration from pre- to post-exercise under each condition.

A study comparing two groups of healthy trained men: one receiving L-citrulline (2.4g/day for 7 days + 2.4g pre-exercise) and the other a placebo, with plasma BCAA levels measured during identical high-intensity cycling. Primary outcome: difference in post-exercise plasma BCAA concentration between groups.

A study using stable isotope-labeled BCAAs to directly measure whether L-citrulline increases BCAA oxidation rate during exercise, confirming the proposed mechanism of increased utilization.

A study observing trained men who self-select L-citrulline use and comparing their plasma BCAA dynamics during exercise to non-users, to see if a pattern of lower BCAA levels emerges.

A small study tracking plasma BCAA levels in a group of trained men before and after taking L-citrulline for 7 days + pre-exercise dose during a single workout.