Nitric oxide (NO) is a gas produced by the endothelium — the single-cell lining of every blood vessel. When released, it signals smooth muscle in the vessel wall to relax, widening the vessel and increasing flow. This is the mechanism behind exercise flush, warm hands and, yes, erections.
Endothelial NO production falls roughly 10–12% per decade after 40. Oxidative stress destroys NO faster than it is made. Smoking, high blood sugar and inactivity accelerate the loss.
Aerobic exercise is the single strongest stimulus. Dietary nitrates (beets, leafy greens) and the amino acid L-Citrulline provide substrate. Polyphenols from Pine Bark and Grape Skin protect NO from breakdown. Maxorin combines the last two approaches.