This brand never fails to deliver a stylish shoe, and the Ultra Boost 21 is no exception.
While I did not have a problem, I am sure people with a higher volume foot will have issues.
In terms of performance, the Ultra Boost 21 is not very propulsive and didn't give me the level of responsiveness that I wanted to pick up the pace.
They felt clunky, stiff and firm.
I am also a midfoot striker and thought that there was way too much padding in the heel for me.
Nike fixed the problem in the second version of the React Infinity Run Flyknit by changing the bootie construction and the shoe improved tenfold.