An increase in muscle mass occurs when the rate of muscle protein synthesis is greater than the rate of breakdown. For muscle growth to occur you have to create a stress that is different to the level that your body has already adapted to by lifting heavier weights, or by changing exercises so that you can damage more muscle fibres. During the rest period following training muscles regenerate and grow as long as they are provided with ample fuel.

After training muscle-glycogen (stored energy) is depleted and increased cortisol levels are beginning to breakdown muscle tissue (catabolic state) and the only way to reverse this is to consume a quickly digestible post-workout meal within ½ hour to an hour, or to ensure that you have had adequate protein before starting training by drinking your protein shake or eating a meal containing some protein.

Protein is needed to build and repair muscle and carbohydrate to replenish muscle glycogen. The surge of carbohydrates and amino acids from a quickly digested meal or your high-protein milkshake (containing protein and glucose) causes an insulin spike that puts nutrients into the muscle cells. Ensure that you consume protein with carbs in a ratio of 1 protein:2 carbohydrates.

It is healthy to train in the morning before breakfast for some people, but it very much depends on the individual. Some research indicates that training before breakfast works better in men than in women, but this is not always the case.
In the morning your body is usually in a fasted state with low blood sugar as you have not eaten since the evening. Therefore once any stored energy (glycogen) is used your body will go into fat-burning mode for energy to fuel your training. This system of energy production is less efficient than using carbohydrate so it may make training feel more difficult. The upside is that if you are trying to lose weight you will start to burn fat reserves. The down side is that your performance may not be as good as when you have eaten and therefore you may find it difficult to train to the same degree (especially if you are doing intense resistance training or high intensity interval training). Also training in a fasted state may cause more muscle breakdown compared to if you have eaten.