Body Systems & Exercise

Exercise helps your heart, lungs, muscles, and bones work better and stay healthy.

Reading is good — doing is better. Practice Body systems & exercise as an interactive lesson.

Definition

Your body is made up of different systems that each do a special job. When you exercise, you help all of these systems grow stronger and work together. Your heart pumps blood faster, your lungs breathe in more air, your muscles get bigger and stronger, and your bones become denser. Exercise is any movement that makes your body work harder than usual.

Remember the rule

Move More = Stronger Heart + Bigger Lungs + Tougher Muscles + Denser Bones

Key words

Heart: The muscle in your chest that pumps blood all around your body.
Lungs: The two organs in your chest that bring oxygen into your body when you breathe.
Muscles: Body parts made of stretchy tissue that pull on your bones so you can move.
Bones: The hard parts inside your body that hold you up and protect your organs.
Cardiovascular system: The team of your heart and blood vessels that moves blood and oxygen everywhere in your body.
Respiratory system: The team of your lungs and airways that brings fresh air in and pushes stale air out.
Oxygen: A gas in the air that your body needs to get energy and keep working.
Muscular system: All the muscles in your body working together to help you move, lift, and balance.

Worked examples

You run one lap around the track. What happens to your heart?

→ Your heart beats faster — maybe jumping from about 70 beats per minute at rest to over 120 beats per minute — so it can pump extra blood and oxygen to your working leg muscles. · You can feel this by placing your hand on your chest right after you run.

You do jumping jacks for 30 seconds. Why do you start breathing harder and faster?

→ Your muscles need more oxygen to keep moving, so your lungs breathe faster to pull in more fresh air and push out carbon dioxide waste. · Breathing harder is your respiratory system doing its job well.

You do push-ups every day for a month. What changes in your arms?

→ The muscles in your arms and chest slowly get bigger and stronger because exercise causes tiny muscle fibers to grow back a little thicker each time they are worked. · This is why athletes practice the same moves over and over.

You jump rope at recess three days a week. How does this help your bones?

→ The light pounding of jumping sends signals to your bones to build more bone material, making them denser and harder to break. · Weight-bearing activities like jumping, running, and skipping are best for bone health.

After sitting all afternoon, your friend says she feels tired and stiff. What would help?

→ Taking a 10-minute walk or doing some stretches would get her heart pumping, her lungs moving fresh air, and her muscles warmed up, helping her feel more awake and less stiff.

Why does your face turn red when you exercise hard?

→ Your cardiovascular system sends more blood close to the skin surface to help cool your body down, which makes your skin look red or flushed. · This is completely normal and shows your body is working hard to keep a safe temperature.

Common mistakes

Thinking only your muscles change during exercise — your heart, lungs, and bones are all changing too.
Believing you need to exercise for a very long time to get benefits — even 10 to 15 minutes of active play helps your body systems.
Confusing the cardiovascular system with just the heart — it also includes all the blood vessels like arteries and veins.
Forgetting that rest matters — muscles actually grow and repair during rest time after exercise, not only during the workout itself.
Thinking exercise only helps your body — it also helps your brain focus better and can improve your mood.

FAQs

Why does my heart beat so fast when I run?

Your muscles need lots of oxygen to keep moving, so your heart speeds up to pump blood — which carries oxygen — to your muscles faster. The harder you work, the faster your heart beats.

Is it bad if my lungs feel like they are burning when I run hard?

A little burning feeling is normal when you push yourself because your lungs are working extra hard. If it hurts a lot or you cannot catch your breath, slow down and rest. Always tell an adult if breathing feels very difficult.

How many times a week should kids exercise?

Health experts say kids should get about 60 minutes of active movement most days of the week. It does not all have to happen at once — recess, walking, dancing, and sports all count.

Do I have to play sports to exercise?

No! Any activity that gets you moving counts as exercise. Dancing, riding a bike, swimming, playing tag, or even raking leaves all help your body systems get stronger.

Why do my muscles feel sore the day after I exercise a lot?

When you work your muscles harder than usual, tiny fibers inside them get small tears. Your body repairs those tears and makes the muscle a little stronger. That soreness is a sign your muscular system is rebuilding.

Can kids damage their hearts by exercising too hard?

For healthy kids, exercise is safe and good for the heart. The heart is a muscle and gets stronger with regular activity. If you ever feel chest pain or dizziness during exercise, stop and tell an adult right away.

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