Myoplasticity is the ability of a muscle to change and adapt. Muscle is very adaptable, but the extent of change is limited by genetics. Any muscle changes are based on the interaction of your energy intake, hormones, recruitment, and load.
Energy intake refers to nutrition. Adequate nutrients and calories must be consumed for any growth process. Special focus should be given to protein intake because muscle is made up of amino acids which are the building blocks of protein. With improper nutrition the body may actually break down muscle for fuel and this would limit any potential muscle growth.
Your hormonal profile during and after exercise can also facilitate muscle growth. Anabolic hormones, those which foster growth and building, increase in response to a single exercise bout and with exercise training.
Recruitment and load refer to the exercises you do. A muscle must be activated in order to adapt. The exercises you choose to do must stress the muscles you are trying to improve. Heavier loads will recruit more muscle fibers and only fibers that are recruited will improve.