In abbreviating the name used for cardiovascular exercise to just cardio, some confusion has arisen about what cardiovascular exercise is. Because the word cardio means heart, and heart rate is used during cardiovascular exercise, the common thought is that cardio is about strengthening your heart. We often refer to good cardio as ‘getting your heart rate up’.
Let’s take a little stroll through what happens in your body when you do cardio and see if there is more to cardio than its name implies.
The start of movement: When you start moving, your brain initiates the action by sending messages to your muscles to move. Therefore, cardio starts in, depends on, and changes your brain and nervous system.
The fuels: As your muscles start to move, they need fuel. There are two main systems for producing fuel for muscles: a long-acting, with-oxygen (aerobic) system and a short-acting, without-oxygen (anaerobic) system.
Since oxygen is carried by the blood, and at rest, only about 20% of your blood flow goes to your muscles, when you start to move your body has to shift your blood flow to those muscles. It takes a few minutes for your muscles to get enough oxygen to use the longer-lasting system for fuel production. So for about the first three minutes of movement, your muscles get their fuel from carbohydrates stored right in the muscles.
Once your body redirects more blood to your muscles, your body can use the longer-lasting, with-oxygen system to keep you moving. This system uses mainly a combination of fats and carbohydrates to fuel muscles. But to do that, it needs the oxygen sent to it from the lungs, pumped through the heart, and transported through your blood vessels.
The equipment: Once your muscles are using the aerobic system for fueling your muscles, you are able to sustain that movement as long as that system has the equipment and fuels it needs. The equipment includes enzymes, mitochondria in cells, glucose, and blood supply, just to name just a few.
Use it to keep it: This equipment is kept sharp by use. If it is not used regularly, it starts to fade. In fact, this starts to happen after just three days of not doing a cardiovascular-type exercise. (If you are on bedrest, it happens even sooner.) This is why cardiovascular exercise is recommended at least three days a week to keep this equipment sharp and working well.
The heart: When the muscles are moving, they are contracting and pressing against your veins. This continuous, rhythmic movement helps the blood travel back to your heart after your muscles have used the oxygen and nutrients they need for that activity. When that blood comes back to the heart, it causes a little stretch in the heart muscle. Think about a balloon filled up with air without tying it. If that balloon has a little bit of air and you let it go, it does not go very far. But if that balloon is filled with a lot of air, and you let it go, it has power to go all over the room. When your heart fills with more blood, that stretch causes it to contract harder. Just like the balloon filled with air, the more blood that returns to your heart, the stronger that contraction.
A stronger heart: This stronger contraction is what is making your heart muscle stronger. The more muscles that are moving, the more blood gets sent back to your heart for that little stretch and stronger contraction. Moving your fingers continuously would send just a very small amount of blood back to your heart. Dancing using your arms and legs sends a much greater volume of blood to strengthen your heart.
Way beyond heart rate: Many things get your heart rate up—stress, caffeine, medications, even just thinking about exercise—but that does not make your heart and cardiovascular system stronger. What makes something good cardio is this challenge to your whole cardiovascular system. Every part of that system gets stronger when you do continuous movement using a large amount of muscles at a level you can sustain.
That sustainably of movement is what makes something cardio. There is much information about how hard you should push your body when doing cardio. I’ll talk about this aspect of cardio in the next blog.