Muscle is a type of soft tissue in the body that enables movement. It is made up of cells that can contract and relax, allowing for various actions like walking, lifting, and even breathing. There are three main types of muscle: skeletal muscle, which moves bones; smooth muscle, found in organs; and cardiac muscle, which makes up the heart. Muscles work by contracting in response to signals from the nervous system. They require energy, primarily from ATP (adenosine triphosphate), to function effectively. Regular exercise can strengthen muscles, improve endurance, and enhance overall health.