I bought these to help with rehab walking after a stroke. I knew it would be a little unstable with not all my muscles capable of responding. I can tell that my thigh muscles as well as my calf and shins have been worked much more than in regular shoes. I walk differently after using these for even a short time. However it is not all better.  I seem to walk locked out a little more because it is safer for me. My body frequently does things in way that is more stable rather than doing it the right way. I really have to concentrate on making my legs flex more. They are a reasonably comfortable fit. Sauconys usually fit me the best.