Why does periodization or as I prefer to call it Planned Performance Training (PPT) have to be either linear or undulating? Frankly in my application of the principles of planned performance training for 49 years I have observed that adaptation is always undulating. The body does nothing in a linear manner, so therefore all periodization is undulating. I think this distinction is just another exercise in intellectual gymnastics. You may write a linear program, but the response will not be linear. I have analyzed my training results over my coaching career; I have NEVER seen a linear adaptation! Planning is planning; we must remember that it is always about the individual and their adaptive response. Variability and contingency must be built into the plan. Plan, execute the plan, evaluate the plan, revise the plan and execute the revised plan.