If you get your leg in a position of unstable equilibrium, any impulse one way or the other takes a small amount of energy. Small energy inputs are easy to reverse, so the frequency can be fairly high. I'm betting that that "high" frequency is somewhere around 2, maybe 5 Hz.
For an example of unstable equilibrium, think of a ball at the top of a hill, exquisitely balanced so that the slightest impulse one way or the other will cause it to roll down the hill. Look at your leg(s) when they are in a position where you can repeat the motion, and notice how easy it is to make it go one way or the other. You are oscillating about a position of unstable equilibrium, most likely.
For an example of unstable equilibrium, think of a ball at the top of a hill, exquisitely balanced so that the slightest impulse one way or the other will cause it to roll down the hill. Look at your leg(s) when they are in a position where you can repeat the motion, and notice how easy it is to make it go one way or the other. You are oscillating about a position of unstable equilibrium, most likely.
If you get to thinking you’re a person of some influence, try ordering somebody else’s dog around.
