Has anyone tried MBT sneakers? They are a sneaker that causes you to exercise your legs and back and supposedly helps posture. The sole of the shoe curves upward towards the heel, forcing you to keep yourself balanced. I bought a pair last month, and have been wearing them most everyday to run around in when doing errands -- I can feel the burn in my thighs, calfs and shins. Yesterday, I wore them while doing my regular walk in the park, but had to stop after twenty minutes because my legs were so tired. Has anyone else tried them? I would be interested to know your experience with them. Thanks, Michele.