Distance events in track are anything from the 800 to the 3200m in highschool and 800-5000m in college.Due to the nature of distance races primarily relying on aerobic conditioning the training one must do starts in the winter 3 months before the season begins .There are 2 phases one must go through to make sure that their aerobic conditioning is strong enough for the demands of a long season of racing and improvements.
Base building, in the simplest of terms, is easy running to build aerobic fitness. It largely consists of adding pre-calculated mileage over the course of a few weeks at a conversational pace to build strength and stamina. This is your foundation for more quality work. A body builder didn't wake up benching 300 lbs, they had to develop the strength over time and allow their body to adapt through stress and recovery. The same way one would during base phase. A good amount of mileage to build up to as an 800m runner is 30-35 miles per week before transitioning to the next phase of preseason training. For a more in depth explanation about base training.
After a base phase of 6-8 weeks is built the next block will be improving your anaerobic or lactacte threshold.
The anaerobic threshold refers to the highest training intensity you can maintain for extended periods without lactate,building up to a significant degree in your bloodstream. Intensity beyond that point causes lactate to increase rapidly, which, in turn, brings on muscle fatigue more quickly.The faster you run the more lactate you produce but running at or slightly below the lactate threshold will allow your body to adapt and start producing less at whatever current speed your lactate threshold is. Threshold runs are very stressful on your body and your blood cells so it is advised to only do threshold runs twice a week at most with base running in between the sessions for proper recovery. Typically one's threshold pace is 80-90% of their max heart rate but if you don't have an heart rate chest strap it is the fastest pace you can run at for 20-25 minutes while still feeling ok afterwards. Threshold training is where you will get the most bang for your buck effort-wise while running, increasing the speed before you build lactate and are forced to slow down is the most important thing for a disance runner.