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.
This video on supination resistance from PodChatLive was a discussion with all the key researchers and theorists on the topic: