Hey, sure. We have something called a line of action node which accepts a 2 point curve as input and feeds into the zFiber node. In this setup, for each zFiber, there is a curve and a line of action node. This node allows you to bias or amplify excitation based on the length of that curve.
Fiber excitation in this way is additional to any values set on the excitation attribute on the zFiber node itself, meaning you can auto fire and also key or drive excition on the same zFiber.
The yellow represents full activation of the muscle, red is unactivated.