Race walking at varied intensity levels trains the many energy systems used by the body during a race. The second phase of training, the interval training phase, trains the body to race walk progressively closer to your selected racing pace. A few months into a training program, your body is unprepared to race at your targeted pace. Therefore, you must begin with slower walks and work up to race pace. Completing a full interval training phase and then a peaking phase develops your ability to sustain your targeted race pace for your entire race distance.
During this phase, your weekly training consists of three hard workouts and three easy workouts. Notice the significant decrease in weekly mileage when you start this phase. This compensates for the added stress your body takes on when increasing workout intensity.