Dr. Andy Galpin

We don't want it to necessarily be extremely large either.

And so if the back end grows, but the chamber size, the balloon size stays the same, then we're going to be able to contract with more force and not compromise our total blood flow.

If you achieved an adaptation like that, and it allowed you to pump out more blood per pump,

That number is called stroke volume.

So the volume of blood that comes out per stroke or per contraction.

The percentage of the blood that gets emptied out of that ventricle is called your ejection fraction.

So let's just say there was 100 milliliters of blood in your left ventricle and you contracted and 50% or 50 milliliters was left in the ventricle, your ejection fraction would be 50.

And so we would like to see high ejection fractions so that we're not wasting our time contracting and blood still sitting in the ventricle.

If you improve either of those things, and I'm going to really focus mostly on stroke volume here, that will allow your heart rate to drop.

And so one of the classic adaptations we see of any type of physical training, but think more specifically endurance type training, is a reduction or a drop in resting heart rate.

See, at rest right now, as you're sitting here listening, the amount of oxygen required

is the same whether you're fit or unfit.

It doesn't necessarily matter.

There's a minimal amount of oxygen based on your body size and other factors that don't really matter your fitness level.

And so we call that your cardiac output, okay?

So what that is is it's the stroke volume multiplied by your heart rate.

So how much is coming out per pump and how many times are you pumping in a given minute?

You multiply those together and you get a cardiac output.

Let's just say that number is five liters per minute.

It's a very standard resting cardiac output.