Hey @Jack_Russell_Racing, I plan to cover this tomorrow in more depth so I’ll keep it short & sweet here.
First point, I wouldn’t consider any workout a “failure” if it routinely pushed you to a high level of O2 uptake/maxed out breathing via repetitious work that jacked up your breathing rate again and again for one simple reason: time at VO2max is more of a concern than hitting a particular power at VO2max.
Say you know from a lab test that your power at peak O2 uptake is 300w, would it be a successful workout if you hit that value for 3x3-minute intervals and a workout failure if you hit it for 30 seconds 18 times with only 15-second recovery valleys between surges? They both accumulate 9 minutes at a particular power, but the latter format probably held you at a higher level of O2 uptake for far more of that 9 minutes.
Similarly, you can reach VO2max at all sorts of different power outputs, so putting a single number on your VO2max power work is tough (impossible, actually) unless you tie it to a particular supra-FTP duration.
Clear as mud? I’ll elaborate tomorrow and I’ll try to get back in here to clarify matters further if this conversation needs the assistance.