Muscles serve the role of providing the body with protection and support for its vital organs, allows for movement, and aids in the production of heat. Usability of muscle is persistent, but muscle growth is determined by the amount of stress exposed to them. Exposure to stress causes microscopic damage to muscle tissue and triggers an immune like response by the release of cytokines to the affected areas. These cytokines are responsible for the repair of the microscopic damage. The higher the progressive demand is on muscles determines the strength and size the muscles would be able to grow. In correlation to usage, the more stress or stimulation muscles undergo, the higher the chances of hypertrophy or increase in muscle mass. The greater the damage, the greater the need for repair. Muscles, like other parts of the body, possesses mechanisms for adaptation. Adaptation in this case would be the accommodation of strength and mass for the amount of stress applied to muscles required for movement. With this, it is recommended to undergo a cycle of applying stress to the muscles, eating, getting rest, and repeating this trend for bigger and stronger muscles. An important aspect in muscle growth is rest. Rest provides the body to recuperate and repair its tissues.  

Age and gender also play a role in muscle growth and development. This is due to the amount of hormones each demographic group may have. Testosterone, insulin growth factor, and varying abilities for repair are all factors that vary muscle growth.