Breathing in and breathing out
Lungs do not have any muscles, so they cannot move air on their own. Instead, muscles in the chest make the lungsexpand, or blow up like a balloon, as air is sucked in. Most of the work of breathing is done by muscles that raise the ribs, but if you breath out hard, for example when blowing a trumpet, you use muscles on the front of your belly as well. This pushes your insides upwards, squeezing the air out of your lungs more forcefully.

Big breathers
People take, on average, more than half a billion breaths during a lifetime. Each person's lungs move about 250 000 m3 (8 million cu ft) of air, a quantity that would fill the biggest airship ever built.