If you cut the string that holds up a Halloween skeleton, all the bones fall to the ground in a heap. That’s just what would happen to you if you had no muscles.
Muscles are the parts of the body that let you stand, walk, run, bend, and reach. They make it possible for you to smile, cross your fingers, and roll your eyes. They are even involved when your mouth waters at the thought of your favorite food.
Muscles let you move your body in so many ways. And they do it all so simply—just by contracting and relaxing. When they contract, muscles pull on the bones or tissue where they are attached, and that pulling enables you to move. When they relax, muscles enable you to rest.
Every human body has over 600 muscles. Some are small, thin, and delicate. Others are tough and sturdy. Together, your muscles make up from 25 to 45 percent of your weight, and each muscle plays a role in keeping you alive and healthy.
