My arches are KILLING me!

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Hey, any other flat-footed FB folks? I have big flat Hobbit stompers with *very* shallow arches, and even with my Sauconys and gel orthotics my arches are SCREAMING through HIIT. Painful cramping is making keeping my feet planted properly very difficult, especially during lunges and squats, which is leading to my knees taking a lot more stress than they should. Anyone have any tips? Or just keep playing through the pain?