This document discusses different models of periodization for training, including linear, block, concurrent, conjugate, and undulating models. It explains that periodization aims to maximize adaptations to training by systematically varying training variables like volume, intensity, and exercise selection over periods or cycles. This allows for periods of overloading and recovery to reduce injury risk while continually progressing an athlete. The document compares advantages and disadvantages of different models for different athlete abilities and sport types to help choose an appropriate periodization approach. It emphasizes that periodization strategies should evolve over time with advances in understanding physiology and the developing needs of individual athletes and sports.