The work load must be fairly demanding. The work load must be a mixture of different methods and types of training. Progress the work load from volume first to intensity towards the end. The third and final key to the training principles is balance. You must balance you training, do not overwork one system and neglect another.
Balance is the key to consistent times later into the cross season.
These principles are just guidelines to help you develop a solid program. They are to be considered to assure the right foundation to build you program on. Two systems of training exist. The systems are Repetition system and Natural system. Here are explanations and some examples of each system.