In general, our doctors recommend a gym shoe with more support than less support.  Although a flexible gym shoe may appear fashionable and comfy, beware!  The lack of support may cause overuse injuries, such as a tendinitis or plantar fasciitis, and even a stress fracture if you are doing high impact exercise on a flexible flimsy gym shoe.  Remember to look for a gym shoe with a solid heel that does not collapse in your hand when you pinch the sides together.  It should flex at the toe, where your foot naturally bends; it should not bend at the arch. More sturdy gym shoes can also better accommodate your orthotics. Wearing flexible shoes occasionally for casual wear might be OK, but just be careful when increasing activity - you don't want to end up with an injury due to lack of support.