I’ll throw this in – as Chad noted, it is possible to increase VO2 max even if one had many years of solid training behind them. But, if you can’t increase overall training volume (jumping from 10 hrs/week to 16 or 18, say), then the VO2 improvement may be in the form of being able to hold your maximum aerobic power for longer durations – not necessarily in the form of raising the watts you generate at maximum aerobic power.
My personal n=1 : when I look at the “flatline” on my 4min intervals, it’s usually at 385-390w, depending on motivation and freshness. At the start of the year, I can hold that ~385 for about 4 minutes – there’s no spike at the start of end of my efforts up that 1 mile, 6% hill.
The 4min power goes up as I do more :30 and 1:00 power work, in addition to some VO2 – and the times up that hill drop, and the average watts go up, but only because now I’m getting these twin peak intervals (which is not a bad thing because that’s how hills tend to play out in races). The flatline I can repeat for 4-5 intervals is still 385, though.
But, the duration that I can hold that 385 steadily goes up – now, in the last few weeks of my last Build, I can hold 385w for 10min. If I did a tapered and fresh 4min, the flatline would probably be a few watts higher than early in the year, but I know from previous years it won’t be much.
Yes, FTP has gone up – but it hasn’t pushed up VO2, it has just risen as a percentage of VO2.
Like SST intervals in Base, sometimes those VO2 intervals are not about “more power in 3-5 min” but about “how can I keep stretching how long I can hold this power.”