You’ve probably heard some variation of “I hate cardio!” or “I love cardio!” from your workout or running partners. Love it or hate it, training your cardiovascular system requires a little clarity to some key questions: How well does running stimulate that system? And how can running help you improve your cardio fitness?
Let’s start with some system basics. “Cardiac” refers to the heart, that singular, essential muscle that pumps blood through your body. And “vascular” refers to your pipes—your veins, arteries, and tiny capillaries—which deliver blood pumped by the heart to muscles, organs, and everything else that needs to be sustained with nutrients and oxygen. Put the two words together and you’ve got the cardiovascular system: the pump and pipes working to power and sustain everything you do, including running.
All of this heart-pumping, oxygen-delivering work goes on constantly, even when you’re just sitting on a couch. But when you further stress this system by running, the system responds and adapts. Muscles, including the heart, get stronger. The pipes become more efficient, adding bigger and more effective lines to power those hard-working muscles.
And while your muscles need oxygen to work efficiently, they can carry on with the work of running, at least for a little while, even when oxygen levels are low. “Aerobic” is the term for that work being done with oxygen, and “anaerobic” is the low-oxygen version. So you’ve got two basic systems, the aerobic and anaerobic, that power your running. (VO2 max scores measure when you’ve hit the top end of your anaerobic threshold.)