GLOSSARY

Arginine contributes to protein, the urea cycle and nitric-oxide production and can be conditionally essential. A pathway role is not a guaranteed supplement-induced blood-flow increase.

During some growth stages or severe illnesses, internal synthesis may fail to meet demand despite being adequate in health. This must be defined for the particular compound and condition. One hard workout alone does not make every compound conditionally essential or justify supplementation.

Amino acids also supply non-protein compounds: arginine participates in nitric-oxide production and tryptophan in serotonin pathways. Such roles do not mean a supplement increases the final product without limit. Enzymes, regulation and other substrates control pathway use, so a mechanism alone does not establish a practical sporting benefit.

Amino-acid nitrogen is transferred, reused or excreted; some becomes urea in the liver and is eliminated through the kidneys. The carbon skeleton has separate metabolic fates. This normal process alone does not diagnose kidney injury, although established kidney disease requires an individually appropriate dietary protein plan rather than automatic use of sport targets.