Supination Resistance is a clinical test that is used to determine how hard or easy it is to supinate the foot. The test was first described by Kevin Kirby DPM. The test is performed clinically by placing two fingers under the posterior part of the arch and using the fingers to supinate the foot and raise the arch – an estimation of how resistant the foot is to supination is made. This helps decide how much force is needed to come from a foot orthotic. If the supination resistance force is high, then if a foot orthotic is needed, then it will have to push hard to resist that force or it may be less likely to work. If the foot orthotic pushes too hard in someone with a lower supination resistance, then it might sprain the ankle as it pushes to hard for the foot.
The clinical test became more popular in response to the understanding that “overpronation” was not the problem that is was widely assumed to be and the realization that it may not be the motion of pronation that is the problem, but more the force that are associated with that overpronation. The forces that are associated with the forces driving pronation are assumed to be the same as the forces needed to supination the foot, hence the name for the clinical test of supination resistance. There is also the understanding that forces are what does the damage to the tissues and not motion that does the damage. One study has found a very poor correlation between the posture of the foot and the forces needed to supinate it.
The test is associated with several different pathologies. It tends to be much harder to supinate a foot in those with posterior tibial tendon dysfunction and much easier to supinate the foot in those with peroneal tendonitis. Other pathologies and conditions are not related to the test.
There has been plenty of discussion on Podiatry Arena about the test. Probably the best summary and review of the evidence is this blog post by Craig Payne. This encyclopedic entry on PodiaPaedia is also worth checking out.