Introduction
You start your workout full of energy. At first, your breathing is calm, maybe you can even talk or smile. But as the pace picks up, your breaths get faster. Your chest rises and falls like a pump working at full speed.
Minutes later you’re gasping for air, convinced there’s never enough of it. Your chest burns as if you were running away from danger. And then the question hits you: what’s really going on inside your lungs when you exercise?
Scientifically
During exercise, your muscles demand far more oxygen to keep producing energy. To handle this demand:
Breathing rate shoots up (from about 12 breaths per minute at rest to 40–60 during intense effort).
Inhalations become deeper, allowing your lungs to pull in extra air.
Carbon dioxide (the waste gas) builds up much faster, so your lungs must work harder to flush it out.
Not only do your lungs work, but so does your diaphragm and other breathing muscles. Over time, training strengthens them, making your breathing more efficient even under heavy effort.
In Everyday Terms – With Workers
Imagine your lungs as a warehouse with big doors. At rest, just a couple of workers stroll in and out, slowly carrying in boxes of oxygen and taking out boxes of carbon dioxide. Peaceful, quiet, no rush.
But the moment you start running or lifting weights — the warehouse alarm goes off! 
The doors fly open, and suddenly a whole army of workers rushes in.
Some haul oxygen boxes inside as fast as they can, others throw carbon dioxide boxes out the back.
Everyone’s sweating, shouting, bumping into each other — but somehow they keep the flow moving.
When you finally stop, the workers collapse exhausted. But after every shift like this, they get better, faster, and stronger. Next time, the chaos won’t overwhelm them so easily.
That burning feeling in your chest? It’s not failure — it’s just your hardworking crew pushing themselves to the limit, making sure your body gets the oxygen it needs to keep going.