You use your muscles to move your bones—and thus your body—into different positions. This allows you to walk, stand, jump, pick things up, smile and perform many other actions. These types of muscle are called the skeletal muscles. Other types of muscle keep your heart beating and other organs working. You can make your muscles stronger by exercising, or practising movements.

Types of muscle

Your body has more than 640 muscles. They form about one third of your whole body weight. Strong, rope-like parts called tendons connect the muscles to bones. A special type of muscle, called smooth muscle, forces food along your oesophagus, stomach and intestines. Your heart is made of another special muscle that beats constantly and never gets tired.

How muscles work

Muscles can only work by pulling. To move the arm, for example, muscles must work together in pairs. The brain sends a signal to the biceps muscle. The biceps shortens, pulling the arm bones upwards. This also causes the triceps to lengthen. To lower the arm, the triceps shortens, and so the biceps relaxes to its original shape.