In order for muscles to grow, three things are required: 1. Stimulus - exercise is needed to make the muscles work, use energy and cause microscopic damage to the fibers. 2. Nutrition - after intense exercise the muscles need to replenish their stores of fuel. 3. Rest - it is during the rest or recovery phase that the muscles repair the microscopic damage and grow. Muscle size increases due to hypertrophic adaptation and an increase in the cross section area of individual muscle fibers. Intensive exercise impacts more on the strength influencing fast twitch type II fibers, therefore the increase in muscle size is accompanied by greater strength. This will deplete the muscle's energy stores and cause microscopic damage to the muscle tissue. During recovery, these stores of glycogen and phosphocreatine will replenish from carbohydrates and creatine ingested as food or supplements. Amino acids supplied in the diet will trigger the protein synthesis that repairs the damaged muscle and lead to the creation of bigger muscle fibers. To achieve continuous improvement you will need to keep reaching for higher levels of training intensity otherwise the improvement process will grind to a halt. Fortunately, this is relatively easy to plan for provided certain basic principles and rules are clearly followed. Subsequent articles in this series will examine these principles in detail.