This is my second pair of Fitflops. I'm still wearing the original black ones that I bought 3 years ago, about the time that they became available in the U.S. These are the most comfortable flipflops ever, with very good support. I can run around in them for an entire day and never feel tired. But I didn't notice any "workout" effect with my first pair, and I don't notice it with these either. I do a lot of walking, running and stair climbing in daily life, so my calves are pretty well toned in any case. Maybe someone who doesn't do that much walking around would notice more of an effect with these sandals.

I paid the original $49.99 price for my first pair (not at Amazon). I wouldn't have bought a second pair for that price, but the $28.00 price for the royal blue was irresistable. I'm glad I didn't resist.