Periodization is a planned change in your training variables over time to reach a particular training goal. These variables can be intensity, volume & frequency. 

Depending on your goal, you change one or more of these variables over time to reach an explicit goal, maybe a competition, a photo shooting, or a PR attempt. 

Periodizations are needed to avoid training plateaus, overreaching, and to reach your training goals effectively. If an athlete would train close to its maximum in every session, he will most likely end up in overtraining. So one part of every periodization should deloads. (See deload article) Another important factor is, as already mentioned, the change of training variables over time to reach your goal effectively. Imagine you want to increase your 1RM in dips. You can now try to dip a heavier 1RM in every dip session, but that will most likely not be very effective and sustainable. Better would be to increase the intensity slowly over time and adjust the volume together with it. So once the intensity is going up, you lower the volume of that lift. (linear periodization)

Macro - Meso - Microcycles

You probably have heard about these before. Marco, Meso & Microcycles describe a certain period of your training. The macrocycle is the whole time frame you set up. So, for example, the time you have until your main competition of the season happens. 

Mesocycles describe the different phases of your training until the end of the macrocycle. Let’s say you have your main competition in 4 months. Four months would be a macrocycle. Now, depending on your training structure, you can set up the mesocycles. You could choose two mesocycles of 2 months, or four mesocycles of 1 month or even more individual. Each mesocycle has some own goals that will help you to achieve the end goal of the macrocycle. These goals in our example could be to work on the perfect technique for a lift, get rid of a specific weakness you have in one lift, work on higher volume to get a better foundation for the upcoming heavy stuff, or many more. Just keep in mind that every mesocycle should be a benefit to the bigger picture, the macrocycle. 

The smallest time frame of this system is the microcycle. The microcycle is your training week. So the number of individual training until they repeat. Depending on the split and frequency you train, this can vary. For our example, we choose a microcycle to be seven days long. So now it comes to setting up the individual training. You know the big picture, you broke it down into different phases, the mesocycles and now you design the individual sessions adjusted to the goals you set up. So you now can choose a split, a frequency that works for you, and you start to select exercises and the volume & intensity for each of it. 

Once you have all set up, you can start training. Of course, once you began to exercise, you will need to adjust your program from time to time since progress doesn’t always happen as planned.

Example with 4 mesocylces: