Dr. Andy Galpin

It's not meant for explosive power or sprinting or jumping or anything like that.

If you were to compare that to the other major muscle in your calf, the gastrocnemius, that's almost the exact opposite.

In a lot of folks, it is 60 plus to 70 or 80% fast twitch fibers.

So the gastroc is there for the exact opposite.

It is there for the explosion, for the jumping and sprinting, and not necessarily to keep you upright all day.

Now, that's not necessarily true of other animals.

In fact, this is one of the things that makes examining research in this area important to pay attention to, whether you're looking at a study from a rat or a mouse, a cat, a bear, or any other animal, is that it's different.

In fact, mice, the soleus is almost exclusively, if not 100% slow twitch, and other muscles like the plantaris might be the opposite, 100% fast twitch.

And so while there's clearly important information we can gather there, it's not necessarily a direct and equal comparator.

So as I mentioned, the amount of fast twitch and slow twitch, the fiber proportions in the muscle groups varies within your own body.

It also varies from person to person.

So if I were to biopsy myself, as I have several dozen times, I would know and see that, say in my vastus lateralis, the muscle on the outside, which is the most common muscle to biopsy for a number of reasons.

It has the least amount of nerve innervations.

There's no major blood vessels flowing through there.

It's easy to access.

It tends to be quite large.

I don't have to go past any other muscle groups, et cetera, et cetera.

So within that muscle, I have seen people in my laboratory as high as 90% plus slow twitch as well as up to 85% fast twitch and everywhere in between.

And so the quadricep, again, the VL specifically here, is meant to really be responsive to training.

And we'll talk about this more later.