Dr. Andy Galpin

One, increase in capillarization, so the amount of capillaries in our exercising muscle.

and or some sort of combination of improved mitochondrial size or content.

If you do those things, you'll be better at extracting the oxygen that's coming in into the tissue as well as utilizing it to go through aerobic and anaerobic recovery metabolism.

Back off of that, we now have stroke volume.

And in fact, one of the things that makes this interesting is as we go towards maximal exercise and start improving our stroke volume, we start to run into a little bit of a problem.

You see, if our heart rate is too high, we don't have enough time to fill the ventricles and arteries back up with blood.

And so we start actually reducing our stroke volume.

And so this is one of the reasons why you would not actually want to have your heart rate continue to increase as a training adaptation.

It's now at the point somewhere around 200 beats per minute or so where it's compromising what's called filling time.

If you don't have enough time there, we can't get enough blood in.

So while you have extremely strong tissue and you can pump a lot of blood out of there per pump, your ejection fraction is massive, right?

You're getting all the blood in the left ventricle out of there every single time you contract.

you've got to have some physical time to actually fill it up.

And so you will see adaptations in the heart tissue itself.

In fact, if you look at the actual size of the left ventricle, kind of an average number to think about there is like 150 grams or so in a non-athlete, where it may be upwards of 200 in an athlete, is something that we see respond and is generally associated as a positive adaptation to exercise.

And so we know we need to increase the strength of the left ventricle as a starting place.

If we do that,

that will allow or actually produce and result in an increase in stroke volume.

So what does that mean for training?

Well, fundamentally, outside of things like exercise technique and timing and nutrition and all that other stuff, if we're just talking about the background physiology, we have two avenues or areas to push on to improve our VO2 max.