Tensing can provide orthogonal control during fingertip movement

Joint movement in the human body happens according to the principle of antagonist contraction: as the result of pairs of opposing muscles combining their tensions.

Rather than joint movement, could this combined tension form a basis for the control of musical sound?

The answer is yes: We can apply a force wave to the fingertip, and then extract a scalar degree of freedom (DOF) tracking finger tensing.

Moreover, it is possible to then implement tensing control that occurs simultaneously with, but separately of, fingertip control based on up/down movement.

This is described here (and, more precisely: here, starting at p.137) and demonstrated in a video here.