Each muscle is made up of thousands and thousands of individual cells called muscle fiber.
while the number of muscle cells/fibers do not increase, each individual muscle fiber has the potential to increase in size density and efficiency.
The number one way to increase muscle mass is resistance training.
Maintaining Posture: Muscle functions almost continuously, making one tiny adjustment after another that enables us to maintain an erect posture despite the never ending downward pull of gravity.
Stabilizing Joints: They stabilize and strengthen the joints of the skeleton.
Generating Heat: Muscles generate heat as they contract. This heat is vitally important is maintaining normal body temperature.