Why variety makes you stronger as a runner

I got an interesting question in the Injured Runners Aid Station, “Should I run without my custom orthotics to strengthen my feet?” It seems logical that stronger runners are less prone to injury. The premise behind this question is whether or not orthotics may cause weakness in your feet or legs.  Never ignore your doctor's advice. But you have to ask your doctor the right questions about treatments like custom orthotics. You also have to understand when a little variety might help you become a stronger runner.  Why variety makes you stronger as a runner? That's what we're talking about today on the Doc On The Run Podcast.