How the Heart and Lungs Work During Exercise

Your body's delivery team

When you sprint across a field or climb the stairs, your muscles suddenly need a lot of energy. To make that energy, they need a steady supply of oxygen. Two organs team up to deliver it: your lungs and your heart. Together they form your cardiovascular system (heart and blood) and respiratory system (lungs and breathing).

In this lesson you'll learn how oxygen travels from the air to your muscles, why your heart races during exercise, and how training makes the whole system stronger.

Step 1: The lungs take in oxygen

When you breathe in, air travels down your windpipe into your two lungs. Inside the lungs are millions of tiny air sacs called alveoli. Their walls are so thin that oxygen can pass straight through into your blood.

At the same time, a waste gas called carbon dioxide passes the other way, out of your blood and into your lungs, so you can breathe it out. So every breath does two jobs:

• Breathe in: bring fresh oxygen into the blood.
• Breathe out: remove carbon dioxide waste.

Step 2: The heart pumps the blood

Your heart is a muscle about the size of your fist, and it never takes a day off. Its job is to pump blood around your body. Blood is the delivery truck that carries oxygen.

The heart has two sides:

1. The right side pumps used blood (low in oxygen) to the lungs to pick up fresh oxygen.
2. The left side pumps the oxygen-rich blood out to the rest of the body.

Blood travels through tubes called blood vessels. Arteries carry oxygen-rich blood away from the heart, and veins carry used blood back to it. The smallest vessels, capillaries, reach right up to your muscle cells to drop off oxygen.

Step 3: Muscles use the oxygen

Inside your muscle cells, oxygen is used to release energy from food (mostly sugars and fats). This is called aerobic respiration ("aerobic" means "with oxygen"). The reaction gives the muscle the energy it needs to contract, and it produces carbon dioxide as waste, which the blood carries back to the lungs.

So the full loop is: lungs → blood → heart → muscles → and back again, over and over, all day long.

What changes during exercise

When you start to exercise, your muscles demand more oxygen and fuel. Your body responds fast:

What happens	Why
Heart beats faster	To pump more blood to muscles each minute
Breathing gets faster and deeper	To take in more oxygen and remove more carbon dioxide
Blood vessels to muscles widen	To send more blood where it's needed
You feel warmer and sweat	Working muscles make heat, and sweat cools you down

This is why you can feel your heart pounding and find yourself out of breath after a hard run. It's your body doing exactly the right thing.

How training builds fitness

The heart is a muscle, so just like the muscles that move your bones, it gets stronger with regular exercise. A trained heart pumps more blood with each beat, so it doesn't have to beat as fast. That's why fit athletes often have a low resting heart rate.

Your lungs and blood improve too. With training, your body gets better at taking in oxygen and delivering it, so you can run, swim, or cycle for longer before getting tired. Activities that make your heart and lungs work harder, like running, swimming, and cycling, are called aerobic or cardio exercise.

To keep this system healthy, doctors suggest children get about 60 minutes of active play or exercise most days. Always build up gradually, and if you ever feel chest pain, dizziness, or can't catch your breath, stop and tell a trusted adult or coach.

Fueling the system

Your heart and lungs work best when your body is well fed and hydrated. Learn what helps in Nutrition for Young Athletes. And before a hard workout, a good warm-up gets the heart and lungs ready gradually, as explained in Why Warming Up Matters.

Quick recap

• Lungs take in oxygen and remove carbon dioxide.
• The heart pumps blood, which carries oxygen to muscles.
• During exercise your heart and breathing speed up to deliver more oxygen.
• Regular exercise makes your heart and lungs stronger and more efficient.

Your heart and lungs are an amazing team working for you every second. Move your body often, and you'll keep that team strong for life!