I'm a lifelong heavy lifter and Animal Pak fills every last nutritional hole I can think of, and then some. Aminos. Vitamins and minerals. Antioxidants. Digestive support. Natural energy. Throw in some of their creatine, Pumps, ZMA, and protein and my stack is complete (well, almost... I still replace their Cuts with BELDT: Force Thermogenic since it helps me lean out a lot easier). And I DEFINITELY feel when the Pak isn't there too, because everything suffers. Strength, recovery, stamina, all of it. Especially recovery. Tore my right quad three months back, so I doubled up the Paks (was only using 1 before) and cut my down-time almost in half.