Don't get Stressed about "Optimal" Training Volume

Training volume is super overrated. 

Intensity and consistency are king. 

If wanting to increase volume, I, personally, recommend doing so by increasing training frequency.

For example: if you're hitting each muscle 2 times per week, instead of doing more sets per session, bump up your frequency per muscle group (or a given muscle group) to 3 times per week.

Short, sustainable sessions done with intensity make it easier to maintain adherence, which makes it easier to sustain serious progress long term.