I am aware of that for exercising, but was ignorant of what "intense" actually means in this context. And you're right.
Looking around, the simplest wording I get:
> the intensity must be high. This means that you need to really exert yourself so you get out of breath. [https://norwegianscitechnews.com/2026/05/exercise-a-very-lit...]
So if climbing the stairs gets someone out of breath it's intense (and I also see how getting to your limits, whatever they are, can help)
There (for example) is High intensity interval training.
What that is depends somewhat on who you ask but to give an example.
Take a normal exercise like cycling for 45 minutes.
If you do HIIT you cycle as fast as you can for 10-15 seconds (or until properly worn out) then rest long enough to be able to do it again. You only end up working out for less than one minute or just half a minute in total but you get similar if not better results than the 45 minutes workout.
So yes, running up the stairs as fast as you can until you feel like you are going to die would be high intensity. Take the elevator back down or you might die for real.
Yeah, typically "intense exercise" is implying HIIT style cardio.
More and more studies have been indicating that even just a few minutes of intense exercise can outperform long/slow LISS type cardios.
E.g. 5m all out effort is probably better, or at least equivalent, for health than a 30m moderate effort.
The average person can likely hit the 80/20 benefit threshold at less than 30m/week.