eli5: how does cardio exercise increase your stamina to do more cardio?

Question

It makes sense that legs get stronger and build muscle, making cardio easier. But how does cardio make it easier to breathe and run longer distances before becoming fatigued and winded?

In: 0

Answer 1

The heart is a muscle and becomes better at pumping blood. The body increases red blood cells and hemoglobin to better carry oxygen, and the muscles become more efficient and use less resources to do the same work.