People take this type of training very, very seriously. I am not an expert on it, although, as someone who grew up playing as a competitive athlete, I can tell you we did a lot of this type of training. I don’t remember hearing the phrase “High Intensity Interval Traning” being used, though it was referred to, circumspectly, by coaches and trainers. For example, we knew the way to get the most out of a run was to throw in some sprints, then actively recover.
I suppose indoor cycling does incorporate this as the class is generally run on an interval principle.
When I say that people take HIIT very seriously, I don’t only mean those who do it get really into it, I also mean that there is normally a huge disclaimer that is only for people who can handle advanced training and who have no medical or health issues. The main reason is that your heart is put under stress by spiking your heart rate and then bringing it back down, then repeating the cycle several times.
I would guess your average FitFiend who incorporates cardio into their regimen, barring any underlying health problems, would have not problem doing this.
Aside from doing spin classes, which I generally do 3 or 4 times a week, I have been trying to do HIIT on the Stairmill. Over the course of about 30 minutes (after a warm up, of course), I would spike the setting to Level 20 for 30 seconds, and at the end of 30 seconds, I would bring it back down to Level 7. For the 30 seconds on Level 20, I would basically be running up the stairs (running, not sprinting). It would get me pretty winded, and my heart rate generally did spike. It certainly was a great workout, although, for the sake of true HIIT, I think that doing it off of a machine is probably better. With a machine, you have to wait for it to increase to the desired level, etc. Also, since I was running up the stairs, I could have still worked harder, but the machine was at capacity.
Results wise, I definitely felt like I had gotten a great workout, and did so in less time than for a comparable jogging workout. Calorie-wise, I am a little skeptical, but maybe if the machine could bring me to a sprinting level, it might have been more comparable.
I know I have been saying this for weeks, but winter is finally over (I hope), and will try to do more HIIT outside, the way it should really be done. It makes a long run a whole lot less boring, trust me. For more information on HIIT, check out this link. HIIT is becoming more and more popular, but it has been around a long time.