From citrulline to the muscle pump
Citrulline is absorbed efficiently and converted to arginine in the kidneys, raising plasma arginine more reliably than taking arginine directly, which is largely degraded on first pass through the gut and liver. The higher arginine then supplies nitric oxide synthase, the enzyme that produces nitric oxide in blood-vessel walls. Nitric oxide relaxes vascular smooth muscle, widening vessels and increasing blood flow to working muscle, which is the basis for the sought-after pump sensation.
Citrulline is often sold as citrulline malate, where the malate component is sometimes claimed to aid energy metabolism, though that part is less well supported.
How robust the pump and performance claims are
The pharmacology of raising arginine is solid, but translating it into consistent performance gains is more mixed; some trials show modest improvements in training volume or reduced soreness, others show little. The acute pump is real but cosmetic and transient.
This is general educational information, not medical advice. Citrulline can lower blood pressure and interact with nitrates and erectile-dysfunction medication. Consult a qualified professional before use.