When it comes to training distance runners, coaches often get caught up in copying another successful coach's training plan in hopes that, by doing so, their athlete will become just as successful as the program they're modeling after. However, what works for one athlete will never work exactly the same for another athlete. This is where one of the fundamental principles of training, individualization, comes into play. I will cover individualization in further detail in a later post, but for now I will use some of its basic qualities to show how it applies to periodization.
In general, periodization is how an athlete's training, diet, rest, etc. is designed in order to develop a peak at a certain time. For some, a peak is desired at the state or national meet; For others, it may be the Olympic Games or IAAF World Championships. Regardless of the event, the date of the peak is the starting point and the most important part of periodization. Afterall, every bit of the training is geared toward that date.
Once that date is found, the coach should start going backwards from that date and generalize the training modalities. This, again, is where individualization comes into play. If you are training an 800 meter runner, then their "base building" phase may be longer in calendar duration, their long runs may be longer, etc. It is important to know which physiological system you are trying to stress for that particular training period and what stimulus will cause that stress. Be sure to include recovery training as well, depending on where your philosophy lies with that matter.
Once you have these components laid out and generalized, the real periodization begins. Physiologically, the human body makes about 95% of a complete adaptation to a stimuli after 18-21 days. Most coaches use 21 days to ensure maximal adaptation and because it fits well with our calendar system. The last 5% of that adaptation would take another 14-21 days, so coaches typically deem that last 5% unnessary and use that time to introduce a new stimulus. Once again, be sure to take individualization in to account with the adaptation period. For example, younger athletes may be unable to handle a steady 21 day cycle, so you may need to cut it to 14-16 days.
Just because a cycle's focus is on one physiological system, does not mean that every workout should stress that system. A good rule for distance runners is to stress the system every other day with a "mileage day" or "recovery day" in between. Also, many coaches believe that the long run is a necessary component every week despite the week's main focus. The long run is a severe physiological stess in itself and needs a "recovery day" before and after it. That usually leaves only 2-3 more days in the week to achieve a full stress for the system you are training.
After the 3 weeks of steady stimulus, some coaches like to insert a "down week" before introducing the body to a new stimulus in order to repair the damage to bodily structures. Other coaches, however, prefer to insert a new stimulus immediately after the initial 21 day adaptation. You can make your own choice based on your philosophy and the individual factors that weigh in on your decision. For example, some coaches are very limited to how much time they have with an athlete and may need to risk injury if they need to achieve a peak within a shorter time frame. Always consult the athlete and review their history of injury before risking an injury relapse.
As the training period gets closer to the targeted peak, the training stimulus should change appropriately depending on the physiolocal demands of the event. With all of this being said, be sure to use this information as well as other OPINIONS and develop your own ideas. Remember, just because it works for one person, doesn't mean it will work for you.