The principle of variation refers to the constant manipulation of specific variables within a training program.
Planned variations (periodization) in an integrated training program are necessary to provide continuous adaptations to occur over a training period, help to prevent injury lead to superior physical, physiological, and performance improvements compared to a non-periodized training program.
Some of the most important variables to consider are:
1. Volume (sets, reps, etc.)
2. Movement Pattern (exercise selection, plane of motion, etc.)
3. Repetition Tempo
4. Rest Interval
5. Neural Demand