Many new runners complain they can't breathe—even on short runs. Getting enough air is foremost on their minds.
Runners get frustrated with their lungs because they perceive them to limit their ability to run. They claim they "can't breathe" while running and are forced to stop so they can "catch their breath." Even trained runners feel this way.
At first glance, distance running seems to have everything to do with big, strong lungs. After all, it's through our lungs that we get oxygen. But if the size of your lungs mattered, why are the best runners in the world quite small people, with characteristically small lungs?
It's a marvel of physiology that enough air gets into your body, with your nostrils being no larger than the size of a pea. Even the space between semi-pursed lips is small considering the physiological demand for oxygen at high intensities.
A large man who, at rest, breathes about half a liter of air per breath and about six liters of air per minute, breathes nearly 200 liters per minute while running hard. That's 53 gallons of air entering the lungs each minute! Try filling a hose with 53 gallons of water in one minute. It gives you a lot more respect for the lungs.
Your lungs' capacity for holding air is mainly influenced by body size, with bigger people having larger lung capacities. Research has shown the lungs do not limit your ability to perform endurance exercise, especially if you're not elite. That limitation rests on the shoulders of your cardiovascular and metabolic systems; blood flow to and oxygen use by the muscles are the major culprits. There is no relationship between lung capacity and how fast you run a 10K.