Originally posted by aka23
If the intervals were sufficient intensity, then yes, I would consider it HIIT. You can do HIIT on a cycling machine, on a treadmill, on an elliptical trainer, on a 400m track, or in any other environment that is provides sufficient intensity. I consider this intensity to be high enough that you quickly get out of breath and cannot continue for more than a couple of minutes without lowering the intensity. For many people this is about 85% MHR or more.
Several of the key HIIT studies were done on cycling machines. The one that I have seen most frequently quoted is the Tremblay "Impact of exercise intensity on body fatness and skeletal muscle metabolism", which is summarized at http://www.exrx.net/FatLoss/HIITvsET.html
. This study was done on cycling machines. The HIIT group did traditional cardio for the first 5 weeks. I assume this was to get in shape for the HIIT. After week 5 the HIIT started off with 15 second intevals on a cycling machine at 60% max 10 second output and 60 second intervals at 70% max 90 second output. The duration and intensity of the intervals increased as the weeks went on. The HIIT group lost more than 3x as much fat (as measured by skinfolds) as the endurance training group even though they burned less than half the calories during the activity.
Having said that, many of these studies were done with untrained persons who can easily get their HR to high levels on a cycling machine. I find it quite difficult to get my HR up to high levels while on a cycling machine. Below are graphs of my heart rate during interval training on a treadmill and a cycling machine. The treadmill involved 15 one min high/one min low intervals. I was able to get my HR up to 97% of estimated maximum by the 13th interval. The cycling involved 3 hill programs with 90 second intervals, 60 second intervals, and 30 second intervals. I was only able to get my heart rate up to about 80% of estimated maximum on the cycling machines.