Originally Posted by burritos

I get it. Exertion to the point of collapse. It's a level that's unsustainable. That's why you stop, hence making it an "interval". For any individual this level(heart rate specific) may be different. I conflated this with climbing hills. But most cyclists don't collapse with maximal exertion cause they can also let up and maintain a minimal level of forward progress. But you can maintain a high heart rate even though the physical output is objectively low. So if you climb a at 2 mph, it's sustainable, and you're not crushing any records, but you can experience a high HR that makes it HIT'ish without necessitating the interval rests. I think this would grossly have the same physiologic benefits, though no doubt HIIT is a more efficient way of achieving this adaptation.

I used to be a mountain biker 99.9% of the time. Now I'm road cycling since COVID. Been doing long road hills that I've never done. I'm not training, just doing it. Occasionally I return to my mountain biking. I don't feel any stronger and still feel spent on my MTBing hills. But per strava, I'm PRing hills that I haven't PR'd in over a decade even though I'm doing HIT as opposed to HIIT.