Richard:
There is not definitive answer to this questions. Some athletes periodize and others do not. The reason for periodization is to emphasize the development of certain physical qualities over others. This has worked well historically. If you have a very strong aerobic base then you may get by without much periodization. If you are just starting out and have a weak aerobic base then I think you’ll find it helpful to concentrate primarily on that aspect until it is sufficient before using a less focused approach. How sufficient? AeT to AnT spread < 10%. Scott