I think following is really important:
But here I think it gets blurry and someone should distinguish between Progressive Overload and Progression.
So READ CAREFULLY I THINK WE GET TO THE HOT SPOT:
IF you do 3x8-this is your progression overload stimulus which leads to progression. After each session you notive you get stronger and CAN increase your reps, weight whatever.
If you stall out at some point with 3x8 and thats not because of overtraining or diet-you-as you noticed right-have to increase the demands on the body.
The principle of increasing loading demands.
So WHAT IS an increased demand for the body?
Switching from 3x8 to 5x5 is from the worload perspektive.
But so is switching to 2x20 regarding the metabolical demands, or decrease rest time.
So is to switch to an exercise the body is not used to. A new pattern the CNS has to learn and adapt to.
So is to increase ferquency.
So is to increase volume.
Zatjorski mentions the point of diminishing returns-after a point (which will vary upon lifters) an increase in work will not yield more results but will lead to a diminished effect. You can´t add exercises or sets forever.
Thats why he advocates qualitative changes.
So were is the difference between VARIETY and INCREASING DEMANDS?
In my examples all points mentioned above are increasing demands from different views.
Is a different stimulus a more demanding stimulus?
I say: YES. look at my examples.
LEts make them more specific:
-For strength switching form 3x8 to 5x5 seems logical.
-For sitze switching from 3x8 to 5x5 OR 2x20 might be an option.
-For improving bench switching from barbell bench to close grip bench might be useful to increase triceps strength in your lift. Thats weakness training but also variation. You vary the grip. You change the exercise.
-For improving “chest” switching from barbell bench to dumbbell bench might be an option for this goal.
What I want to say:
The principle of increasing loading demands and principle of variety work close together.That results in Progressive Overload. This allows you to break out of ACCOMODATION and allows again for PROGRESSION.
BUT the new demanding/different stimulus has to be carefully chosen to meet your goals.