Your body moves because your bones, muscles, and joints work together. Bones hold you up, muscles pull on bones to make them move, and joints are the places where bones meet and bend.
Have children bend and straighten their arms while feeling their muscles tighten and relax. Let them find joints by bending different body parts (knees, elbows, wrists, fingers). Try movements like walking, jumping, and twisting to feel different muscles working.
Children often think bones can bend on their own. They do not realize that bending happens at joints, and that muscles are what pull the bones. Some think muscles are only in the arms (biceps) and do not know muscles are all over the body.
Have you ever wondered how you can run, jump, throw a ball, and dance? It all comes down to three things working together: your bones, your muscles, and your joints. Each one has a different job, and none of them could do it alone.
Your bones are hard and strong — they hold your body up and give it shape, kind of like the frame of a building. But bones cannot bend. If you only had bones and nothing else, you would be frozen in place like a statue. That is where joints come in. Joints are the places where two bones meet. Your elbow is a joint. Your knee is a joint. Your shoulder, hip, wrist, and every finger all have joints. Joints let your body bend and turn at those special meeting spots.
But joints do not move by themselves either — they need muscles to make things happen. Muscles are stretchy, strong tissues attached to your bones. When a muscle tightens up (contracts), it pulls on the bone it is attached to, and the bone moves at the joint. Try this: bend your arm and feel the front of your upper arm with your other hand. That hard bump is your muscle tightening as it pulls your forearm up. When you straighten your arm, a different muscle on the back of your arm does the pulling. Bones hold you up, joints let you bend, and muscles do the pulling — teamwork that happens every time you move.