Dr. Andy Galpin

That's the only option it has.

It's all or none principle, all or on.

So the only way that you up or down regulate force output is you turn on more or turn off more of these units.

So,

When you don't do activities that require high force, you don't activate the high threshold motor units because they are exclusively reserved for very high force demand.

And so we see this as a consistent principle across all skeletal muscle, and it holds true in the abs and core as well.

If I told you right now that we wanted to get your quad stronger, and I'll keep coming back to this parallel,

and you said, yes, I want to maximize my muscle size in my quad, I want the biggest quads ever, or I want to break a world record in leg extension strength or something, and I said, awesome, we're going to do wall squats.

You'd be like, what?

Like, awesome exercise, great for muscular endurance, but no one in the history of the world who got the biggest quads ever

Plats didn't do wall squats only, and powerlifters, you get the point here.

Not saying you can't do them, but if that's your only approach, you're going to be very hard to convince any athlete or coach that that is the best way.

That's the same thing you're doing with your abs when all you're doing are planks and three sets of 20 crunches.

You're forgetting the size principle, which is huge numbers of your motor units are not being activated.

When they're not activated, you don't actually get stronger.

You get better endurance, but you don't get them stronger.

The equivalent here exchange would be, yeah, sure, do your wall squats where you're holding that 45 degree position against the wall.

And then also add in some leg presses or leg extensions or whatever leg exercise you like, right?

Fatigue and burning are not the same as force production.

There's an overlap, of course, but you see the major difference here.