Check out this link. We just talked about this same subject on grappler's.com
Also here is something from our physical therapist
I would also add to that...
1. Weak Glut medius which therefore does not allow for good deceleration control as you go into pronation.
2. Tight hip rotators that make your foot have to pronate more to compensate for
3. Tight anterior hip (hip flexor, quad or hip capsule which makes your achilles have to compensate more which inturn creates a greater need for pronation.
4. If pain with running... a tight same side shoulder which does not rotate back as you run causes foot to pronate more on same side.
I know these may seem out there but... I treat it everyday in the clinic. Your body is a series of chain reactions.... Where is the chain have a weak link... Find that you find your problem.
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Hopefully that will help you with your problem