Since my 2017 article was linked on VO2max training, I just thought I’d offer a more contemporary perspective: that there are good reasons to think that high intensity interval training to improve performance does NOT need to be maximal.
There are good arguments that improvements to VO2max are related to exercise intensity. However, we need to recognise that improving VO2max is not necessarily synonymous with improving endurance performance. Let’s be clear what our goals are.
Not trying to takedown anyone in particular, but hearing comments like “blackout intervals” and “waterboarding” has me worried that training consistency (nevermind enjoyability!) might suffer in pursuit of making things hard, for hardness sake. Flexing a ‘no-pain-no-gain’ attitude seems very 1992-high-school-football-coach to me 
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I feel pretty confident saying that just doing the work consistently over time, minimising down-time from overtraining, under-motivation, injury, etc. and prioritising long-term sustainability rather than maximizing any single workout will produce better performance, health, and overall fitness outcomes.
Some discussion from a colleague’s meta-analysis.
*…at any intensity within the severe domain, ie. above FTP / CP / MLSS / etc.
- All studies in the meta-analysis used 2-3 HIIT sessions per week, for 2-10 weeks. So the improved outcomes with increasing number of sessions implies longer sustained training duration over greater number of weeks.