L-Citrulline offers a better choice to boost the body's production of NO. Unlike L-Arg which goes through the digestive system first before being absorbed, L-Citrulline can bypass the digestive system and go directly into the bloodstream, where it can boost nitric-oxide production. NO increases blood flow, letting more oxygen into your muscles by helping blood vessels relax and widen. Better blood flow equals bigger pumps and muscle growth to perform at your best.