Muscle is the stretchy, powerful tissue in your body that contracts and relaxes to create movement. Every time you kick a soccer ball, write with a pencil, or even blink your eyes, you're using muscles. Your body contains over 600 muscles working together to help you move, lift, push, and pull.

Muscles come in different types. Skeletal muscles attach to your bones and let you control your movements, like deciding to raise your hand or run across a field. Smooth muscles work automatically in places like your stomach and intestines, helping digest food without you thinking about it. Your heart is made of special cardiac muscle that beats continuously throughout your life, pumping blood through your body.

When you exercise regularly, your muscles grow stronger and larger. This happens because the muscle fibers actually tear slightly during hard work, then repair themselves thicker and tougher than before. That's why athletes train consistently to build their muscles up.

People also use “muscle” to mean power or force in general. When someone muscles their way through a crowd, they're pushing through with physical strength. If a country has military muscle, it means they have significant power and influence. When you flex your muscles, you're showing your strength, whether physical or otherwise.