what is the fastest speed a human can run
That would mean both reached a speed of roughly 26.5 MPH. Considering that, even the reductions the WR has taken in the last 12 years, it would be okay to assume 27-28 MPH is the fastest speed ever attained by a person running. Though Bob Hayes, in 1964, ran his leg of the 4x100m relay in 8.50 seconds.