Your Amazing Muscles: The Body's Movers

Hold your arm out straight with your palm facing up. Now slowly bend your elbow and bring your hand up toward your shoulder. Do it again and this time place your other hand on the front of your upper arm. Did you feel something? There is a lump that appears and then disappears as you move. That lump is a muscle doing its job. What do you think is happening inside your arm right now?

Muscles are special body parts made of long, stretchy fibres, which are like very thin threads bundled together. You have more than 600 muscles in your body. Their main job is to move your bones. Here is the key idea: muscles can only pull — they cannot push. When a muscle gets shorter, it pulls on a bone and the bone moves. Getting shorter is called contracting. Because muscles can only pull in one direction, they work in pairs. One muscle pulls the bone one way, and its partner muscle pulls it back the other way. Look at your upper arm as a great example. You have two important muscles there. The biceps muscle is on the front of your upper arm. When it contracts (gets shorter), it pulls your forearm up and your elbow bends. The triceps muscle is on the back of your upper arm. When it contracts, it pulls your forearm back down and your elbow straightens. When the biceps contracts, the triceps relaxes and gets longer. When the triceps contracts, the biceps relaxes. They take turns — that is how you bend and straighten your arm smoothly. Your muscles attach to your bones with strong bands called tendons. You can think of a tendon like a tough rope that connects the muscle to the bone so the pull is transferred properly. Muscles need energy to work. That is why exercise makes you feel warm and tired — your muscles are using up energy and working hard.