ZMA is a synergistic blend of two minerals, zinc and magnesium, and a vitamin, Vitamin B-6 or pyridoxine. All three of these compounds are extremely important in biological processes. It has been shown that increased exercise can lead to losses of vitamins and minerals. Zinc is particularly important from a bodybuilding standpoint due to its role in testosterone production. The old story about oysters being an aphrodisiac is probably related to the fact that they are high in zinc. Low levels of zinc and magnesium have a strong adverse effect on muscle growth.