Definition of Racewalking.
Racewalking 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 conact occurs.
The advancing leg must be straightened (i.e. not bent at the knee) from the moment of first contact with the ground until the leg is in the vertical upright position.
Click here for USA Track and Field Race Walking Officiating Handbook.