Does anyone know why, I contract my muscles or stretch them constantly?!

Does anyone know why, I contract my muscles or stretch them constantly?

I used to workout a lot, and I still run on the treadmill daily. I do stretch as much as possible, and am more flexible than average because I used to take martial arts. But I am always flexing, or contracting my leg muscles. What's the deal? Dehydrated? Is it from stretching and running? Anyone else have this problem? I've seen some guys who used to lift a lot of heavy weights do the same thing.

1 week ago
And same goes for my back. It seems like I'm always trying to adjust, or crack my back.

I wonder if it's some outlet for nervous energy. I used to take ballet as a child, even now I find myself pointing and flexing my toes.