We know by now that for muscle growth to occur, you need to eat enough protein, drink enough water, have energy available that can be used to build muscle and a growth stimulus. But, how can you actually achieve that muscle growth stimulus? Muscle tension
A muscle growth stimulus can be reached by incorporating three main principles during your workout. The first main principle is muscle tension. Muscle tension occurs when you lift heavy loads for enough time under tension. This happens when you do the exercise with a good amount of weight and repetitions, the first couple repetitions may be easy, however, the more you get into the set, the harder it gets to contract the muscle because ATP* stores are reduced.
Muscle damage is literally the damage you do to your muscle, micro-tears that happen when you put stress on your muscles. You can experience DOMS (Delay Onset Muscle Soreness). Your body repairs those micro-tears stronger than they were before.
Doing a workout with high-repetition sets puts a lot of stress on the muscles. You might notice this near the end of a high-rep set, you feel a burn or pump. This is the lactic acid that builds up in your muscles as you progress through your set. The build-up of lactic acid will cause a hormonal response which will cause muscle growth.