It is a chemical produced by the body in small quantities responsible for the proper functioning of many systems (especially during intense muscle activity where its concentration/blood is increased to help allocate more blood & oxygen to the muscle tissue and with the recovery). However, shortly after the workout, the concetration is decreased and blood flow to the muscle tissue returns back to the normal rate. The supplement causes the concentration to increase and sustains the rise for the whole day (with a standard dosage of 1-2g). So, technically, the muscle tissue (as well as other body parts) recieve higher quantities of blood flow & nutrients for the whole day, which increases muscle output and speeds up recovery. It increases stamina, strength and endurance during intense muscle activity so one can maximize their workout. I take it before workout, but since it is a free radical, you have to carefully select your diet and make sure that you do not consume any foods rich in anti-oxidants on the same day because these will oxidize any radicals in the body and render them useless. I used to drink 8-12 cups of herbal tea per day (which contains very powerful anti-oxidants), so in order to get the benefits of NO, I had to switch to odd days for tea consumption on which I would not take the supplement. Currently I am taking it 3-4 times a week. Consult your doctor before you take it; this is only for serious body building. Overdoses can cause cancers.