What is the difference in terms of adaptations between say a vo2 max workout like 5x3’ with 4’ rest compared to a group ride where you may do a similar amount of efforts but there could be rest periods of 5 to 15 mins between efforts?
Do you improve your vo2 max uptake the same way but without training yourself to do the efforts over and over on short rest?
It’s time at a high percentage of vo2max that is crucial.
So the issue with the outdoor ride you’re describing is that the rest periods, if truly easy, will allow your aerobic system to recover much more than the 4 minutes on the trainer would. So with each interval, it takes longer to get your heart rate and oxygen uptake up to that level where you’re getting the adaptations.
In my experience, group rides and chaingangs can be great for motivation, as you try to hold the wheel up a hill, or go for just one final sprint when you’re nearly toast. But unless the other riders are looking to do the exact same training as you, it’s very difficult to use them as effective workout replacements.