Arginine
Arginine is a conditionally essential amino acid that serves as the direct precursor to nitric oxide, the molecule responsible for vasodilation and the muscle pump you feel during training. It also supports immune function, wound healing, and the urea cycle.
Why It Matters
Arginine fuels nitric oxide production, which widens blood vessels and improves nutrient delivery to working muscle. That is why pre-workout blends often list arginine alongside citrulline. The catch is that oral arginine has poor bioavailability compared to citrulline, so most modern formulas now favor the latter for pump effects.
Beyond performance, arginine plays a role in clearing ammonia through the urea cycle, supporting healthy immune cells, and aiding tissue repair after intense training blocks.
How to Spot It on a Label
Arginine shows up in two places. On powder amino acid panels, it is listed by grams per serving; whey concentrate delivers around 0.5g per 25g protein scoop. On pre-workout labels, look for L-arginine HCl or arginine AKG, typically dosed between 1 to 3 grams per serving.
Examples from real products
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