In national competition, USATF established an official definition of race walking to formally differentiate it from running. This definition evolved across several decades as officials attempted to better define the sport. Although many rules regulate competitive walking, only this definition (in two parts) serves to characterize legal race walking.
Race walking is a progression of steps so taken that the walker makes contact with the ground so that no visible (to the human eye) loss of contact occurs.
The advancing leg must be straightened (i.e., not bent at the knee) from the moment of first contact with the ground until in the vertical upright position.
One would think by now this definition would be concrete, but in practice, it is fairly subjective.