By definition, Periodisation is breaking up something into time slots, or periods. When playing a competitive sport, this is applied to training to develop the athlete in the optimal way, soliciting peak performance during their competition and not before or after. This means understanding what is most important before, during and after a competition and, therefore, training is split up into three main periods based on this “before, during and after” concept.
Period 1: Preparation — This is the period where non-specific, fitness work is done. It may start off with developing the athlete’s cardiovascular base (the base cardiovascular endurance when given a simple routine) and move on to more complex workouts. General full-body weight training, callisthenics, general speed and agility, balance and flexibility are some of the techniques that may be employed during this phase. Coming to the end of this is a period known as Specific Preparation, where a trainer begins to train an athlete in a manner that is more specific to the sport.
Period 2: Competition — This phase can be split into 2; Pre-competition and main competition. The pre-competition phase is where training gets more specific to the competition that is approaching. A trainer may look at the nature of the competition and train the client to perform optimally in that competition. An example of this is when a football (soccer) team that is accustomed to low-lying fields is going to compete in a hilly or mountainous area, they may engage in altitude training coming closer to the competition. A sprinter preparing to compete in a cold environment may start to run in an air-conditioned arena.
About a week or two before the competition, an athlete goes into the main competition phase. The goal here is to get the athlete to peak during the competition. Training volume may decrease and more emphasis may be placed on recovery methods. This approach is known as tapering (gradually decreasing the amount of work done). It is expected that no major fitness improvements will be achieved in that last week or two and the focus here is twofold; a) to ensure that the athlete does not lose any of his/her fitness by simply not training at all, and b) attempting to prevent injury or general fatigue by limiting the amount of work done. During a long season, earlier events (football matches, races, etc.) are generally regarded as part of training and taken into account when calculating total training volume per week.
Period 3: Transition — This is also known as off-season training. The idea is to rest the athlete’s mind and body after the rigours of an intense competition. The athlete is encouraged to take some rest and relaxation, get a good deep tissue massage, and engage in activities unrelated to the sport. A swimmer may take some time to play golf, a marathoner may go sailing and a cricketer may engage in some football. This period may last 2-4 weeks in general (longer or shorter based on the athlete-trainer relationship) and is focused on getting the athlete ready for his/her next competition cycle.
So, in a nutshell, this is the general approach to soliciting the best performance from athletes during a competition. A trainer may tweak this as he/she sees fit based on the sport and the athlete in question. A phenomenal athlete may need a shorter tapering period to get the same results as someone who has slightly less natural ability. Not all sports employ this method and, even in sports that do, not all organisations, teams and athlete may use it. However, in a general sense, it has proven to get the best competition results over other approaches to training.