Here is personal experience Z2 vs Z3 over 2 similar base periods. Weekly/monthly structure is same (3 weeks loading, 1 week recovery)
- 1st month: 6xZ2
- 2nd month: 1xZ4/1xSS (switched over week) + 5xZ2
- 3rd month: 1xZ4 + 1xSS + 4xZ2
Hard workouts were similar, most difference was how I approached Z2/Z3
- Outdoors: Z2 by HR (70% max HR, or 80% threshold HR), power falls around 58-62% FTP:
- Indoors: Z2/Z3 by power, usually 68-80% of FTP. HR usually around 75% max HR
Note how much more (1) has Z2+Z4 vs (2) has Z3 slightly more but overall volume is much less, while HR Z3 is way higher. FTP improvements were roughly similar (2-3% per block). So, externally looks like same outcome from slightly different input. RHR/HRV/sleeping patterns are also very similar and stable, i.e. recovery should be sufficient.
Now comes “but”: during (1), I was always eager to get to bike. With (2) same until suddenly lost motivation completely, had to take 2 weeks to reset mentally. It may seem like outdoor vs indoor, but it is not – I have seen it earlier with SSHV plan/outdoors as well. All is good for 3 months, getting stronger but suddenly interest is gone.
I imagine, it might be due some kind of slowly growing hormonal imbalance that I do not notice week-over-week until it hits. Obviously we all are different, for you numbers might be different or no such issue at all. But this is something to be aware of and compare long period trends to draw conclusions.