However let me state that I don’t believe that sarcoplasmic growth can happen independently from myofibrillar growth.
Again, I think what a lot of guys see in that is nothing more than cellular volume/swelling that occurs from an increase in training volume, or through metabolic stress (which doesn’t drive growth without mechanical tension either).
What can happen in those modalities is that there’s a higher degree of nutrient partitioning in the muscle which makes it swell due to cell volumization. But there’s no real “growth” that happens.