I work 12 hour shifts on my feet! These shoes are the best shoes out there that help prevent back and joint pain. I have noticed an improved posture as well. I cannot speak for muscle toning because I have only had them for about 1 month. I normally wear a 7.5 shoe (medium width) and I ordered a 7.5 shoe. It fits great. The tongue was stiff for approximately 2 wears. Also, I wore them straight for 12 hours from the get-go without any trouble. It does take a little adjustment, but I wouldn't trade them for the world.