Which way and why are muscles grow?

Major factors of development of muscles are stimulation of muscles fiber and superindemnification. Stimulation arises when your training passes intensively enough to force muscles to adapt for stress, answering on it by increase at a rate of and becoming stronger.

Superindemnification is directly connected to ability of restoration and it is a chain of chemical reactions, which are necessary for your organism to become stronger. Major factors for restoration are duration and quality of rest. From long-term experience it is known, that your ability to restoration does not grow proportionally to your force.

For example, the man with the average natural constitution has an opportunity to increase force in 2,5 - 3 times, before he will achieve a limit of the potential opportunities, and woman accordingly in 2 times. Potential of restoration does not undergo such huge jumps. The more you become stronger, the more attention you should give to abilities of restoration.

To not break process of normal restoration, you should vary duration of training and burdening, which are applied to training process.

Any volume of training is the negative factor, because it exhausts your biochemical resources. Therefore training should be so compressed as far as it possible to avoid overtraining. But the training should promote growth of muscles that determines necessity of high intensity.