Muscle biology is the study of how muscles function and develop in the body. Muscles are made up of cells called muscle fibers, which can contract and relax to produce movement. There are three main types of muscle: skeletal muscle, which moves bones; cardiac muscle, which makes up the heart; and smooth muscle, found in organs like the intestines. Muscle fibers contain proteins such as actin and myosin that interact to create contractions. When the brain sends signals through nerves, these proteins work together to shorten the muscle, allowing for movement. Regular exercise can enhance muscle strength and endurance by promoting growth and repair of these fibers.