There is so much mumbo and confusion in this whole area I am not sure where to begin. Perhaps these thoughts will lend some clarity.
Lets start by defining Periodization, it is the planning and organization of training into a cyclic structure to develop all biomotor qualities in a systematic, sequential, and progressive manner for optimum development of performance capabilities.
Another way to look at it, it is the timing, sequence and interaction of the training stimulus to allow optimum adaptive response in pursuit of specific competitive goals. It is not about time, it is about timing. It definitely is not random, it is always undulatory in nature based on how the body adapts. You can write a linear program, but the body adapts in an undulatory manner. Despite all that is written about the difference between undulatory and linear periodization, in my opinion those are term of convenience, that confuse rather enlighten.
All components must be trained during all phases, only the proportion changes with the training age & stage of training.
There is synergy between all systems of the body and a synergistic relationship between all biomotor qualities. According to Olbrecht, different qualities have different curves of supercomensation (Olbrecht p.5). Because the various qualities have different times to adaptation and fitness decline much slower than fatigue it is possible to achieve continual adaptation.
I use this rule of thumb regarding adaptation time – Tasks that require complete recovery- Usually are high NEURAL demand. Tasks that can be trained with incomplete recovery – Usually are of high METABOLIC demand.
Wave Principle – Continuous alternation of increased and reduced training loads throughout the various training cycles to insure continual adaptation.
Steering Principle – Adjustments in training & competition based on the difference between the planned training & competition results and the actual achieved training & competition results. According to Olbrect “Every loop provides feedback, which is used to plan the next cycle in order to fit in the training process with the individual trainability and so improve the training efficiency and return.”