This video introduces periodization as part of fitness programming. Periodization is the purposeful cycling of training variables over a specified training period. You do this to adjust training stimulus for continual adaptation. You can't always max out one training variable workout to workout, periodization allows you to make progress while you recover.
Linear periodization is basically changing one training variable workout to workout. You can change weight, reps, and sets. Some people feel like that certain non-linear schemes are actually still linear schemes. For our purposes, unless you're increasing a training variable consistently workout to workout then you're actually doing non-linear periodization.
Non-linear periodization is usually where you cycle intensity and volume over a period. Intensity can be measured in weight or heart rate. Volume can be measured in reps, sets, or distance and time.
Non-linear periodization becomes necessary when you've maxed out your linear gains. Eventually, with linear periodization, you will stall.
The time period you choose for periodization should largely be determined by how quickly you can recover and adapt. Sometimes that could be week to week and other times it will be month to month or even longer.
Undulating periodization is where at the end of the trade off cycle we start again. We don't produce a sinusoidal wave of volume and intensity. Instead they look like a crest between them.