I'm curious if this is the same muscle that causes Charlie Horses. I can activate it on its own without moving my leg and can hold it in tension for a long time

I'm curious if this is the same muscle that causes Charlie Horses. I can activate it on its own without moving my leg and can hold it in tension for a long time but if you flex it too hard it knots and is quite painful. The way that I can flex it: Lie on your back on the floor with your heels on a couch, knees approx 90 degrees Tip/rotate your foot forward and you'll feel a large muscle engage Try and flex that muscle like you would your bicep or pectorals. You'll find that you can hold it for quite some time. Edit: I managed to hold it for a few minutes and it's a very odd feeling afterwards. Almost like I had done a bunch of stairs with no cardio. Edit 2: Standing afterwards wasn't fun - I had to stretch my calves out to walk normally.