As will be discussed more on this site, evidence continues to mount that anaerobic training (short sprint-type training) is effective for both anaerobic AND aerobic fitness. One example comes from the latest update on Clarence Bass' website (one of my favorites).
The success story documents how a 32-year-old male trained for a 5k race with no endurance training. Instead, he used the "Tabata" protocol, which involves 20 second sprints with 10 seconds rest in between. Amazingly, this person ran a better 5k time than he did the previous year when he did traditional aerobic training.