If you didn’t have muscles, you wouldn’t be able to move. A muscle is a bundle of tissue cells that tighten up and get shorter when they are at work. This tightening up of a muscle is what makes a part of you move. When that part of you stops moving, the muscle relaxes and returns to its normal size.
Your body has more than 600 muscles, divided into two types: voluntary and involuntary muscles.
When you throw a ball or walk or bend over, you use muscles you can control. These are called voluntary muscles. Involuntary muscles, on the other hand, are those over which you have no control; they work without your even thinking about them.
Your heart is such an involuntary muscle, as it beats to pump the blood through your body. Involuntary muscles also push food through your body’s digestive system.
Your muscles make up about half the weight of your body!