This is a concept that has been getting increased attention in recent years in clinical practice. It is a concept and clinical test of determining how hard it is to supinate the foot based on the assumption that the harder the force is, then if a foot orthotic is needed for something like, overpronation, then more force needs to come from the foot orthotic; so a rigid firm and inverted type foot orthotic is needed. Similarity if the force is low, then not much force is needed from the foot orthotic, so a soft flexible foot orthotic is indicated.
There has been some research done on it, but not a lot. This is probably limiting its more widespread use in clinical practice. The test for supination resistance does correlate quite well with some pathologies and not others.