Systematic variation is a basic principle of training. The key word here is systematic. The variation must be planned and serve a specific purpose in the context of the whole training program. Just throwing a bunch of random different” stuff” into a program is not variation with a purpose. That is confusion and despite what some of the commercial “fitness ‘ programs advertise that is not training, that is entertainment. Variation is programmed as part of an overall plan to allow for continual adaptation. Some relatively simple means of incorporating variation that can have complex implications are:
Hard/Easy – A hard workout followed by an easy workout.
Simple/Complex – A very simple training session followed by a complex training session
Heavy/Light – A heavy day followed by a light day.
Work/Rest – Simply vary work to rest ratios on the some work regimen will stimulate adpatation.
The key is that all these are done with a purpose in pursuit of specific training objectives.