Dr. Andy Galpin

And so while we want to be able to turn skeletal muscle on and off a lot and to have really specific and precise movement, that's not the role of the heart.

In fact, we need to hedge towards something else.

We just want the heart to contract.

We don't need it to contract in different ways.

We don't need high precision.

We need a full contraction.

And in fact, more importantly,

We need to hedge against the possibility of not having a contraction.

If your hamstrings don't fire appropriately, or you think your glutes are turned off, or they're not as strong as you'd like, that's not going to really change your ability to live.

If your heart fails to contract even one time, you have serious problems.

If it fails to do that for just a couple of minutes, you're dead.

And so the demand is quite different.

It needs to be very consistent, and it needs to basically do the same thing every time, and it needs to have fail-safes.

So if some problem exists, it can still contract.

And so the nature of the fibers in your heart are quite different.

In muscle, they're very, very long.

So you'll see them up to five to six inches in length of a single muscle fiber in, say, your quadriceps.

They are quite short and thick in the heart.

The diameter cross-sectional area is roughly the same.

You're talking about something like 4,000 to 5,000 micrometers squared in terms of a cross-sectional area.