Since the onset, the First Endurance products were engineered to work synergistically as a system.  Each product can stand on its own, yet works better when used in conjunction with other First Endurance products.  Here are two examples where this synergy is evident.  1) Complete recovery requires addressing, adrenal stress, muscle tears, glycogen replenishment, antioxidant status and electrolyte balance.  The use of Optygen (adrenal stress) and Ultragen (muscle tears, glycogen replenishment, antioxidant status and electrolyte balance) allows for complete recovery.  2)  The harder one trains, the more calcium and vitamin C that is required. MultiV  has 400mg Vit C, 0mg Calcium while EFS has 120mg Vit C, 100mg Calcium.  Using more EFS when you train long also means you get more Vit C and Calcium, assuring you get the right level of these key nutrients when they are needed.  Finishing your workout with a serving of Ultragen delivers an additional 400mg Vit C and 500mg Calcium.   Many nutrient synergies have been built into the First Endurance system of products so you can be assured of optimal nutrition during all aspects of training.